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From: Mark H Weaver <mhw@HIDDEN>
To: Maxime Devos <maximedevos@HIDDEN>, Ludovic =?utf-8?Q?Court=C3=A8s?=
<ludo@HIDDEN>
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
removing service
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Hi Maxime,
Maxime Devos <maximedevos@HIDDEN> writes:
> On Thu, 2021-04-15 at 14:58 -0400, Mark H Weaver wrote:
>> Maintain historical mappings from user/group names to UIDs/GIDs, perhaps
>> in some file in /etc, where entries are added but *never* automatically
>> removed. When allocating UIDs/GIDs, we would avoid any UIDs/GIDs in the
>> range of those mappings.
>
> This seems rather convoluted to me. Why not reuse /etc/passwd and /etc/groups?
> My suggestion:
>
> 1. *never* automatically delete users/groups from /etc/passwd, /etc/groups
> (I thought that was how Guix already worked ...)
> 2. as users and groups appearing in /etc/passwd and /etc/groups, but not
> in the operating system configuration can be confusing, change the comment
> string of these users and groups, to something like
>
> "account removed"
>
> Add a group 'user-graveyard' for (3), and move these 'pseudo-removed' users
> to the 'user-graveyard' group.
> 3. Don't forget to remove graveyard users from all groups (except user-graveyard),
> make sure the graveyard users can't log in anymore ... (Perhaps add a rule to
> the SSH and PAM configuration that forbids logging in to graveyard accounts,
> by checking whether the user is in the 'user-graveyard' group?)
I would be okay with this approach as well, although it's not obvious to
me that it's any cleaner than having a separate /etc/previous-uids file,
given items 2 and 3 above.
>> Then, provide a UID/GID garbage collector, to be explicitly run by users
>> if desired, which would scan all filesystems to find the set of UID/GIDs
>> currently referenced, and remove entries from the historical mappings
>> that are no longer needed.
>
> That seems useful for if /etc/passwd and /etc/group is getting full, or just for
> cleaning up. You may want to exclude /gnu/store though, for efficiency (-:.
Good point! That's one directory that would clearly be a waste to scan :-)
> And just in case check whether any live processes have the UID/GID.
Sure, sounds good.
Thanks!
Mark
bug-guix@HIDDEN:bug#36508; Package guix.
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From: Mark H Weaver <mhw@HIDDEN>
To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
removing service
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<1576552162.14721.1618320275616@HIDDEN>
<87czuxsya5.fsf@HIDDEN> <875z0pgnqn.fsf@HIDDEN>
<87lf9jiems.fsf@HIDDEN> <878s5j8ga7.fsf@HIDDEN>
<87zgxzgpbf.fsf@HIDDEN> <87tuo645sh.fsf@HIDDEN>
Date: Sat, 17 Apr 2021 12:16:43 -0400
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Hi Ludovic,
Ludovic Court=C3=A8s <ludo@HIDDEN> writes:
> Mark H Weaver <mhw@HIDDEN> skribis:
>
>>> Maintain historical mappings from user/group names to UIDs/GIDs, perhaps
>>> in some file in /etc, where entries are added but *never* automatically
>>> removed. When allocating UIDs/GIDs, we would avoid any UIDs/GIDs in the
>>> range of those mappings.
>
> If we=E2=80=99re just worried about ID allocation, we could keep state in=
, say,
> /etc/previous-uids, and feed that as input to the (gnu build accounts)
> allocation code.
Sounds good to me, or at least better than the other available options.
Thanks,
Mark
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 16 Apr 2021 15:18:16 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Fri Apr 16 11:18:16 2021 Received: from localhost ([127.0.0.1]:41435 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lXQEZ-00024o-PQ for submit <at> debbugs.gnu.org; Fri, 16 Apr 2021 11:18:16 -0400 Received: from eggs.gnu.org ([209.51.188.92]:45860) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <ludo@HIDDEN>) id 1lXQEX-00024b-Mn for 36508 <at> debbugs.gnu.org; Fri, 16 Apr 2021 11:18:14 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:42068) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <ludo@HIDDEN>) id 1lXQES-0002Dg-HG; Fri, 16 Apr 2021 11:18:08 -0400 Received: from [2a01:e0a:1d:7270:af76:b9b:ca24:c465] (port=39092 helo=ribbon) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <ludo@HIDDEN>) id 1lXQES-0001y5-23; Fri, 16 Apr 2021 11:18:08 -0400 From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN> To: Mark H Weaver <mhw@HIDDEN> Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service References: <20190705083620.lbzu7a33awbymh3d@cf0> <1576552162.14721.1618320275616@HIDDEN> <87czuxsya5.fsf@HIDDEN> <875z0pgnqn.fsf@HIDDEN> <87lf9jiems.fsf@HIDDEN> <878s5j8ga7.fsf@HIDDEN> <87zgxzgpbf.fsf@HIDDEN> X-URL: http://www.fdn.fr/~lcourtes/ X-Revolutionary-Date: 27 Germinal an 229 de la =?utf-8?Q?R=C3=A9volution?= X-PGP-Key-ID: 0x090B11993D9AEBB5 X-PGP-Key: http://www.fdn.fr/~lcourtes/ludovic.asc X-PGP-Fingerprint: 3CE4 6455 8A84 FDC6 9DB4 0CFB 090B 1199 3D9A EBB5 X-OS: x86_64-pc-linux-gnu Date: Fri, 16 Apr 2021 17:18:06 +0200 In-Reply-To: <87zgxzgpbf.fsf@HIDDEN> (Mark H. Weaver's message of "Thu, 15 Apr 2021 18:22:49 -0400") Message-ID: <87tuo645sh.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: Brendan Tildesley <btild@HIDDEN>, 36508 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) Hi, Mark H Weaver <mhw@HIDDEN> skribis: > It's true that if you delete a user or group on another distro and then > re-add it, it might not be assigned the same UID/GID. That much is the > same as any other distro. > > The key difference is this: On Debian, at least in my experience, users > and groups are *never* deleted automatically. They are only added > automatically, but never removed unless you explicitly ask to remove > them. So, this problem does not arise in practice. >> Maintain historical mappings from user/group names to UIDs/GIDs, perhaps >> in some file in /etc, where entries are added but *never* automatically >> removed. When allocating UIDs/GIDs, we would avoid any UIDs/GIDs in the >> range of those mappings. If we=E2=80=99re just worried about ID allocation, we could keep state in, = say, /etc/previous-uids, and feed that as input to the (gnu build accounts) allocation code. Thoughts? Maxime Devos <maximedevos@HIDDEN> skribis: > This seems rather convoluted to me. Why not reuse /etc/passwd and /etc/g= roups? > My suggestion: > > 1. *never* automatically delete users/groups from /etc/passwd, /etc/groups > (I thought that was how Guix already worked ...) > 2. as users and groups appearing in /etc/passwd and /etc/groups, but not > in the operating system configuration can be confusing, change the com= ment > string of these users and groups, to something like > > "account removed" > > Add a group 'user-graveyard' for (3), and move these 'pseudo-removed' = users > to the 'user-graveyard' group. > 3. Don't forget to remove graveyard users from all groups (except user-gr= aveyard), > make sure the graveyard users can't log in anymore ... (Perhaps add a = rule to > the SSH and PAM configuration that forbids logging in to graveyard acc= ounts, > by checking whether the user is in the 'user-graveyard' group?) Problem is that things like GDM would still propose those old accounts (unless maybe their password is uninitialized, I=E2=80=99m not sure; but it= =E2=80=99s still hacky.) Thanks, Ludo=E2=80=99.
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 16 Apr 2021 15:14:22 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Fri Apr 16 11:14:22 2021 Received: from localhost ([127.0.0.1]:41424 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lXQAo-0001yA-8f for submit <at> debbugs.gnu.org; Fri, 16 Apr 2021 11:14:22 -0400 Received: from eggs.gnu.org ([209.51.188.92]:44690) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <ludo@HIDDEN>) id 1lXQAm-0001xr-Jr for 36508 <at> debbugs.gnu.org; Fri, 16 Apr 2021 11:14:20 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:41997) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <ludo@HIDDEN>) id 1lXQAg-0000WS-EO; Fri, 16 Apr 2021 11:14:14 -0400 Received: from [2a01:e0a:1d:7270:af76:b9b:ca24:c465] (port=39090 helo=ribbon) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <ludo@HIDDEN>) id 1lXQAf-0001de-W1; Fri, 16 Apr 2021 11:14:14 -0400 From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN> To: Mark H Weaver <mhw@HIDDEN> Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service References: <20190705083620.lbzu7a33awbymh3d@cf0> <1576552162.14721.1618320275616@HIDDEN> <87czuxsya5.fsf@HIDDEN> <875z0pgnqn.fsf@HIDDEN> <87lf9jiems.fsf@HIDDEN> <878s5j8ga7.fsf@HIDDEN> <87wnt3gndy.fsf@HIDDEN> X-URL: http://www.fdn.fr/~lcourtes/ X-Revolutionary-Date: 27 Germinal an 229 de la =?utf-8?Q?R=C3=A9volution?= X-PGP-Key-ID: 0x090B11993D9AEBB5 X-PGP-Key: http://www.fdn.fr/~lcourtes/ludovic.asc X-PGP-Fingerprint: 3CE4 6455 8A84 FDC6 9DB4 0CFB 090B 1199 3D9A EBB5 X-OS: x86_64-pc-linux-gnu Date: Fri, 16 Apr 2021 17:14:11 +0200 In-Reply-To: <87wnt3gndy.fsf@HIDDEN> (Mark H. Weaver's message of "Thu, 15 Apr 2021 19:04:30 -0400") Message-ID: <871rba5kjg.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: Brendan Tildesley <btild@HIDDEN>, 36508 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) Hi Mark, Mark H Weaver <mhw@HIDDEN> skribis: > This particular issue is easily addressed. It's easy enough to find a > function from 31-hash values to 32-bit IDs that's injective and avoids > any chosen subset of special IDs, as long as there are fewer than 2^31 > special IDs. > > Simply adding 65536 (or even 2^31) to the hash value would be one easy > option. > > What do you think? Yes, but these special IDs are just examples of things that could go wrong. I don=E2=80=99t know, maybe I=E2=80=99m just overly cautious; we ha= ve to try to get a better understanding of how things will go! Thanks, Ludo=E2=80=99.
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 16 Apr 2021 10:43:14 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Fri Apr 16 06:43:14 2021 Received: from localhost ([127.0.0.1]:40105 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lXLwQ-0001KR-5C for submit <at> debbugs.gnu.org; Fri, 16 Apr 2021 06:43:14 -0400 Received: from xavier.telenet-ops.be ([195.130.132.52]:33434) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <maximedevos@HIDDEN>) id 1lXLwM-0001KG-Ni for 36508 <at> debbugs.gnu.org; Fri, 16 Apr 2021 06:43:12 -0400 Received: from ptr-bvsjgyjmffd7q9timvx.18120a2.ip6.access.telenet.be ([IPv6:2a02:1811:8c09:9d00:aaf1:9810:a0b8:a55d]) by xavier.telenet-ops.be with bizsmtp id tNj82400K0mfAB401Nj8Un; Fri, 16 Apr 2021 12:43:09 +0200 Message-ID: <38fd9bfdc71c689df1606a0b00d632e423c5defa.camel@HIDDEN> Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service From: Maxime Devos <maximedevos@HIDDEN> To: Mark H Weaver <mhw@HIDDEN>, Ludovic =?ISO-8859-1?Q?Court=E8s?= <ludo@HIDDEN> Date: Fri, 16 Apr 2021 12:42:53 +0200 In-Reply-To: <87eefbidcs.fsf@HIDDEN> References: <20190705083620.lbzu7a33awbymh3d@cf0> <1576552162.14721.1618320275616@HIDDEN> <87czuxsya5.fsf@HIDDEN> <875z0pgnqn.fsf@HIDDEN> <87eefbidcs.fsf@HIDDEN> Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-vI66qH0XHOizTwd9LNSk" User-Agent: Evolution 3.34.2 MIME-Version: 1.0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=telenet.be; s=r21; t=1618569789; bh=6fK+zfjLWh0vsbQPCEOwSVJVNlEj7zV+JoyaknT3oFU=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=ODBkCkzDv+orOTIP6prKoFg+po0S5xknwhiv2Sm66HF1UrE+6lCEvlHwjdLZeEWEa 8Hav+/J0O1WtL5+wjRESNwhnNbUy1/ofQWR07cBpwIHyuChXBCRSEltID+M4OCGb/2 LPas723h5PDHNTqrsZzTjfnhtslRCihz6J4QI9rdPGUmFFiUs/ByEEEfMpGaUlMb5m y8z+jVcNaCMxYoLxG0nxYrJUwb2QVVQCIU56qjoQvOnCO5YSvJuQDIEkS60gI4AP90 cepgikjhWukKQkbTwNI+sdw15oDBnpeZKPMaiZ4Ci/wZX/QV6urJeqBDkOOr9fHOZM mhwGWvj9QNGJg== X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: Brendan Tildesley <btild@HIDDEN>, 36508 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) --=-vI66qH0XHOizTwd9LNSk Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2021-04-15 at 14:58 -0400, Mark H Weaver wrote: > Ludovic Court=C3=A8s <ludo@HIDDEN> writes: >=20 > > Mark H Weaver <mhw@HIDDEN> skribis: > >=20 > > > Here's one idea: when activating a system, *never* delete users or > > > groups if files still exist that are owned by those users/groups. > > > Checking all filesystems would likely be too expensive, but perhaps i= t > > > would be sufficient to check certain directories such as /var, /etc, = and > > > possibly the top directory of /home. And /tmp, /media and /run/user. > >=20 > > How would you determine which directories to look at though? What if w= e > > miss an important one? >=20 > I have another idea: >=20 > Maintain historical mappings from user/group names to UIDs/GIDs, perhaps > in some file in /etc, where entries are added but *never* automatically > removed. When allocating UIDs/GIDs, we would avoid any UIDs/GIDs in the > range of those mappings. This seems rather convoluted to me. Why not reuse /etc/passwd and /etc/gro= ups? My suggestion: 1. *never* automatically delete users/groups from /etc/passwd, /etc/groups (I thought that was how Guix already worked ...) 2. as users and groups appearing in /etc/passwd and /etc/groups, but not in the operating system configuration can be confusing, change the comme= nt string of these users and groups, to something like "account removed" Add a group 'user-graveyard' for (3), and move these 'pseudo-removed' us= ers to the 'user-graveyard' group. 3. Don't forget to remove graveyard users from all groups (except user-grav= eyard), make sure the graveyard users can't log in anymore ... (Perhaps add a ru= le to the SSH and PAM configuration that forbids logging in to graveyard accou= nts, by checking whether the user is in the 'user-graveyard' group?) > Then, provide a UID/GID garbage collector, to be explicitly run by users > if desired, which would scan all filesystems to find the set of UID/GIDs > currently referenced, and remove entries from the historical mappings > that are no longer needed. That seems useful for if /etc/passwd and /etc/group is getting full, or jus= t for cleaning up. You may want to exclude /gnu/store though, for efficiency (-:= . And just in case check whether any live processes have the UID/GID. Suggested command name: "guix user-gc". Greetings, Maxime. --=-vI66qH0XHOizTwd9LNSk Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iI0EABYKADUWIQTB8z7iDFKP233XAR9J4+4iGRcl7gUCYHlqLRccbWF4aW1lZGV2 b3NAdGVsZW5ldC5iZQAKCRBJ4+4iGRcl7iLeAQCDp8ywXTcQrPOsnQ427HUGcXmo W23thxgqzXqSPwy5ZAD9EoGaIgOLrMymibzhCeJ/alf6nGRxQjonoxZ9cyuq5A0= =Ht7l -----END PGP SIGNATURE----- --=-vI66qH0XHOizTwd9LNSk--
bug-guix@HIDDEN:bug#36508; Package guix.
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From: Mark H Weaver <mhw@HIDDEN>
To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
removing service
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Hi Ludovic,
Ludovic Court=C3=A8s <ludo@HIDDEN> writes:
> IDs as hash of the user names are interesting because that=E2=80=99d be
> stateless (conversely, the current ID allocation strategy is stateful:
> it arranges to not reuse recently-freed IDs.)
>
> But like you write, we=E2=80=99d need 32-bit UIDs. In libc, =E2=80=98uid=
_t=E2=80=99
> (specifically =E2=80=98__UID_T_TYPE=E2=80=99 in typesizes.h) is 32-bit, s=
o it might work
> rather well in user space.
The kernel and core system components certainly support 32-bit UIDs, and
have for around 20 years.
> It still sounds like a change with significant implications though, and
> it=E2=80=99s hard to predict exactly how it would go or what would break.
Right, my concern is with the vast majority of programs and libraries in
Guix, most of which probably haven't seen much (if any) testing with
large UIDs.
> For example, that does away with the system/non-system ranges, and
> wouldn=E2=80=99t play well with =E2=80=9Cspecial=E2=80=9D IDs like 0 and =
65535.
This particular issue is easily addressed. It's easy enough to find a
function from 31-hash values to 32-bit IDs that's injective and avoids
any chosen subset of special IDs, as long as there are fewer than 2^31
special IDs.
Simply adding 65536 (or even 2^31) to the hash value would be one easy
option.
What do you think?
Mark
bug-guix@HIDDEN:bug#36508; Package guix.
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From: Mark H Weaver <mhw@HIDDEN>
To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
removing service
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Hi Ludovic,
Ludovic Court=C3=A8s <ludo@HIDDEN> wrote:
>>> Note that the ID allocation strategy in (gnu build accounts) ensures
>>> UIDs/GIDs aren=E2=80=99t reused right away (same strategy as implemente=
d by
>>> Shadow, etc.). So if you remove =E2=80=9Cbob=E2=80=9D, then add =E2=80=
=9Calice=E2=80=9D, =E2=80=9Calice=E2=80=9D won=E2=80=99t
>>> be able to access the left-behind /home/bob because it has a different
>>> UID.
I replied:
>> This mechanism is insufficient, because it only avoids the problem if
>> you add "alice" at the same time that "bob" is removed. If you remove
>> "bob" during one system activation, and then later add "alice", then
>> "alice" might well be able to access bob's left-behind files.
Ludovic Court=C3=A8s <ludo@HIDDEN> responded:
> To be clear, it=E2=80=99s doing the same as any other GNU/Linux distro.
I don't think that's quite right.
It's true that if you delete a user or group on another distro and then
re-add it, it might not be assigned the same UID/GID. That much is the
same as any other distro.
The key difference is this: On Debian, at least in my experience, users
and groups are *never* deleted automatically. They are only added
automatically, but never removed unless you explicitly ask to remove
them. So, this problem does not arise in practice.
Thanks,
Mark
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 15 Apr 2021 20:05:49 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Thu Apr 15 16:05:49 2021 Received: from localhost ([127.0.0.1]:39313 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lX8FI-00071p-KT for submit <at> debbugs.gnu.org; Thu, 15 Apr 2021 16:05:49 -0400 Received: from eggs.gnu.org ([209.51.188.92]:35706) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <ludo@HIDDEN>) id 1lX8FG-00071a-2R for 36508 <at> debbugs.gnu.org; Thu, 15 Apr 2021 16:05:47 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:43756) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <ludo@HIDDEN>) id 1lX8FA-0006fw-8H; Thu, 15 Apr 2021 16:05:40 -0400 Received: from [2a01:e0a:1d:7270:af76:b9b:ca24:c465] (port=38568 helo=ribbon) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <ludo@HIDDEN>) id 1lX8F8-0006Z9-Qx; Thu, 15 Apr 2021 16:05:39 -0400 From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN> To: Mark H Weaver <mhw@HIDDEN> Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service References: <20190705083620.lbzu7a33awbymh3d@cf0> <1576552162.14721.1618320275616@HIDDEN> <87czuxsya5.fsf@HIDDEN> <875z0pgnqn.fsf@HIDDEN> <87lf9jiems.fsf@HIDDEN> X-URL: http://www.fdn.fr/~lcourtes/ X-Revolutionary-Date: 26 Germinal an 229 de la =?utf-8?Q?R=C3=A9volution?= X-PGP-Key-ID: 0x090B11993D9AEBB5 X-PGP-Key: http://www.fdn.fr/~lcourtes/ludovic.asc X-PGP-Fingerprint: 3CE4 6455 8A84 FDC6 9DB4 0CFB 090B 1199 3D9A EBB5 X-OS: x86_64-pc-linux-gnu Date: Thu, 15 Apr 2021 22:05:36 +0200 In-Reply-To: <87lf9jiems.fsf@HIDDEN> (Mark H. Weaver's message of "Thu, 15 Apr 2021 14:30:40 -0400") Message-ID: <878s5j8ga7.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: Brendan Tildesley <btild@HIDDEN>, 36508 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) Hi Mark, Mark H Weaver <mhw@HIDDEN> skribis: > Ludovic Court=C3=A8s <ludo@HIDDEN> writes: > >> Note that there are other places, in addition to GDM, where we >> forcefully reset the UID/GID of the home directory (e.g., for the >> =E2=80=98knot-resolver=E2=80=99 service.) >> >> My preferred solution to this would be to unconditionally chown -R home >> directories upon activation (for efficiency, it would be best if we >> could do that if and only if the home directory itself has wrong >> ownership). Thoughts? > > It might be okay to do this in specific cases like /var/lib/gdm, but I'm > very uncomfortable doing it for *all* users, because: > > (1) We shouldn't assume that all files within a home directory are > supposed to be owned by that user. > > (2) We shouldn't assume that all files owned by a user will be within > their home directory. > > (3) We shouldn't assume that all files within a home directory are > supposed to have the same 'group'. I, for one, have sometimes had > subdirectories of my home directory with a different 'group', to > either restrict or grant other users access to selected files or > directories. > > (4) Groups do not, in general, have home directories. > > (5) I consider it unsatifactory for there to be *any* window of time > during system activation when the ownership of files is incorrect. I agree this raises questions and we should take time to think through it. For system accounts though, I think 1=E2=80=934 do not apply. Perhaps a first step would be to do that for system accounts? >> Note that the ID allocation strategy in (gnu build accounts) ensures >> UIDs/GIDs aren=E2=80=99t reused right away (same strategy as implemented= by >> Shadow, etc.). So if you remove =E2=80=9Cbob=E2=80=9D, then add =E2=80= =9Calice=E2=80=9D, =E2=80=9Calice=E2=80=9D won=E2=80=99t >> be able to access the left-behind /home/bob because it has a different >> UID. To be clear, it=E2=80=99s doing the same as any other GNU/Linux distro. > This mechanism is insufficient, because it only avoids the problem if > you add "alice" at the same time that "bob" is removed. If you remove > "bob" during one system activation, and then later add "alice", then > "alice" might well be able to access bob's left-behind files. > > In the case that I personally witnessed on my Guix system, files within > /var/lib/gdm ended up with 'colord' as their group. That's not good. > > Increasingly, I'm leaning toward the idea that the complete mapping from > names to IDs should somehow be explicitly given as part of the OS > configuration, as I advocated in <https://bugs.gnu.org/36508#26>. > > What do you think? IDs as hash of the user names are interesting because that=E2=80=99d be stateless (conversely, the current ID allocation strategy is stateful: it arranges to not reuse recently-freed IDs.) But like you write, we=E2=80=99d need 32-bit UIDs. In libc, =E2=80=98uid_t= =E2=80=99 (specifically =E2=80=98__UID_T_TYPE=E2=80=99 in typesizes.h) is 32-bit, so = it might work rather well in user space. It still sounds like a change with significant implications though, and it=E2=80=99s hard to predict exactly how it would go or what would break. = For example, that does away with the system/non-system ranges, and wouldn=E2=80= =99t play well with =E2=80=9Cspecial=E2=80=9D IDs like 0 and 65535. To me, it=E2=80=99s a potential way out, but not a solution for the bug Bre= ndan reported today, nor a change we could implement in the coming weeks/months; the time scale is probably longer. WDYT? Thanks, Ludo=E2=80=99.
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From: Mark H Weaver <mhw@HIDDEN>
To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
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Ludovic Court=C3=A8s <ludo@HIDDEN> writes:
> Mark H Weaver <mhw@HIDDEN> skribis:
>
>> Here's one idea: when activating a system, *never* delete users or
>> groups if files still exist that are owned by those users/groups.
>> Checking all filesystems would likely be too expensive, but perhaps it
>> would be sufficient to check certain directories such as /var, /etc, and
>> possibly the top directory of /home.
>
> How would you determine which directories to look at though? What if we
> miss an important one?
I have another idea:
Maintain historical mappings from user/group names to UIDs/GIDs, perhaps
in some file in /etc, where entries are added but *never* automatically
removed. When allocating UIDs/GIDs, we would avoid any UIDs/GIDs in the
range of those mappings.
Then, provide a UID/GID garbage collector, to be explicitly run by users
if desired, which would scan all filesystems to find the set of UID/GIDs
currently referenced, and remove entries from the historical mappings
that are no longer needed.
What do you think?
Mark
bug-guix@HIDDEN:bug#36508; Package guix.
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To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
removing service
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Ludovic Court=C3=A8s <ludo@HIDDEN> writes:
> My preferred solution to this would be to unconditionally chown -R home
> directories upon activation
I also wonder if this could lead to security flaws similar to
CVE-2021-27851 <https://bugs.gnu.org/47229>, but perhaps 'chown' has
been written carefully to avoid such problems.
Mark
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From: Mark H Weaver <mhw@HIDDEN>
To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
removing service
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Ludovic Court=C3=A8s <ludo@HIDDEN> writes:
> Note that there are other places, in addition to GDM, where we
> forcefully reset the UID/GID of the home directory (e.g., for the
> =E2=80=98knot-resolver=E2=80=99 service.)
>
> My preferred solution to this would be to unconditionally chown -R home
> directories upon activation (for efficiency, it would be best if we
> could do that if and only if the home directory itself has wrong
> ownership). Thoughts?
It might be okay to do this in specific cases like /var/lib/gdm, but I'm
very uncomfortable doing it for *all* users, because:
(1) We shouldn't assume that all files within a home directory are
supposed to be owned by that user.
(2) We shouldn't assume that all files owned by a user will be within
their home directory.
(3) We shouldn't assume that all files within a home directory are
supposed to have the same 'group'. I, for one, have sometimes had
subdirectories of my home directory with a different 'group', to
either restrict or grant other users access to selected files or
directories.
(4) Groups do not, in general, have home directories.
(5) I consider it unsatifactory for there to be *any* window of time
during system activation when the ownership of files is incorrect.
>> Here's one idea: when activating a system, *never* delete users or
>> groups if files still exist that are owned by those users/groups.
>> Checking all filesystems would likely be too expensive, but perhaps it
>> would be sufficient to check certain directories such as /var, /etc, and
>> possibly the top directory of /home.
>
> How would you determine which directories to look at though? What if we
> miss an important one?
Yes, that's a good point. I suppose that my idea above is not
satifactory either.
> Note that the ID allocation strategy in (gnu build accounts) ensures
> UIDs/GIDs aren=E2=80=99t reused right away (same strategy as implemented =
by
> Shadow, etc.). So if you remove =E2=80=9Cbob=E2=80=9D, then add =E2=80=
=9Calice=E2=80=9D, =E2=80=9Calice=E2=80=9D won=E2=80=99t
> be able to access the left-behind /home/bob because it has a different
> UID.
This mechanism is insufficient, because it only avoids the problem if
you add "alice" at the same time that "bob" is removed. If you remove
"bob" during one system activation, and then later add "alice", then
"alice" might well be able to access bob's left-behind files.
In the case that I personally witnessed on my Guix system, files within
/var/lib/gdm ended up with 'colord' as their group. That's not good.
Increasingly, I'm leaning toward the idea that the complete mapping from
names to IDs should somehow be explicitly given as part of the OS
configuration, as I advocated in <https://bugs.gnu.org/36508#26>.
What do you think?
Thanks,
Mark
bug-guix@HIDDEN:bug#36508; Package guix.
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From: Mark H Weaver <mhw@HIDDEN>
To: Brendan Tildesley <btild@HIDDEN>, 36508 <at> debbugs.gnu.org
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
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Hi Brendan,
Brendan Tildesley <btild@HIDDEN> writes:
> Guix system rollbacks should be a supported feature of Guix, not just a gimmick
> that falls out of its design. It should be that a Guix user could leave their
> system for 5 years, and then do a guix pull; guix system reconfigure in the year
> 2026. Perhaps at that time the new system will break, and then its desirable
> that they can rollback to the previous generation.
This sounds like a good set of goals to strive for. I'm not sure that
Guix, on its own, will be able to achieve reliable 5-year rollback. I
think that would require _all_ software in Guix that maintains mutable
state on disk to gracefully support downgrading to a version from 5
years earlier.
Nonetheless, Guix can certainly do its part to try to ensure that
multi-year rollbacks can work, and I agree that it's a good thing to
keep in mind.
> So what fixes we put in to
> Guix services today need to consider not just how files could have changed in
> the past, but how they might change in breaking ways in the future, within reason.
It's a good thing to keep in mind, yes.
> I don't know off the top of my head of any way that can be done other than to
> have chmod -R gdm:gdm /var/lib/gdm always executed.
I'm not necessarily opposed to doing that, at least as a temporary
workaround for GDM, but I don't think this is a satisfactory solution to
the larger problem. A few points:
(1) I don't think we can assume that all files owned by a given user
will be in that user's home directory, especially for "system"
users.
(2) I also don't think we can assume that all files in a user's home
directory *should* be owned by that user. Even if it's true today,
it might not be true tomorrow.
(3) Groups don't even have home directories.
> On 04/13/2021 10:51 PM Mark H Weaver <mhw@HIDDEN> wrote:
>>
>> There's some discussion of this issue at <https://bugs.gnu.org/44944>,
>> although I'm not sure that Danny's suggested solution is practical.
>>
>> Here's one idea: when activating a system, *never* delete users or
>> groups if files still exist that are owned by those users/groups.
>> Checking all filesystems would likely be too expensive, but perhaps it
>> would be sufficient to check certain directories such as /var, /etc, and
>> possibly the top directory of /home.
>>
>> What do you think
>
> Wouldn't that imply that uids could be randomly different on different systems
> with the same configuration, and then remain statically different permanently?
Yes, and I agree that it's suboptimal.
> We want as little randomness and moving parts as possible. It's yet another
> way the system is not actually Functional, but has state.
Agreed. Danny's suggested solution (UID = hash username) is clearly the
optimal approach in many respects. It has the nice properties above.
The practical problem I see with Danny's approach is that in order to
make hash collisions sufficiently improbable, our UIDs and GIDs would
need to be much larger than the 16 bits that is widely supported by
POSIX software. With 16-bit UIDs, the probability of a collision would
be 1.85% with 50 users, and 7.28% with 100 users.
To adopt this approach, I think that our UIDs and GIDs would need to be
at least 31 bits. These are the problems I see:
(1) It's unlikely that all software in Guix robustly handles such large
UIDs/GIDs. Desktop systems with UIDs/GIDs larger than 65533 have
not been widely tested, as far as I know.
(2) Even with 31 bit IDs, the probability of collisions would still be
uncomfortably high when large numbers of users are present: with 10k
users, the probability of hash collisions would be about 2.3%.
(3) We'd need a transition plan for users' existing file systems.
(4) It would be aesthetically unpleasant for our UIDs and GIDs to be
random-looking numbers with 10 decimal digits.
> Seems this bug spans 3 or so different bug reports. In http://issues.guix.gnu.org/45571
> I commented that Nix uses hard coded id's, sorta like how ports are allocated
> for a purpose:
>
> https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/misc/ids.nix
>
> Perhaps you are thinking of other kinds of security issues that could be caused that
> I'm not thinking of.
I'm not sure what you're getting at here. The only security issue I've
raised so far is that ownership of files can _effectively_ be changed
when removing services and later adding them back. For example, in my
case, 'colord' ended up being the owner of files in /var/lib/gdm.
> In that case maybe Nix devs have already made the best choice by
> making them static?
That might well be true. At the present time, this is the option that
seems most appealing to me.
One possible approach would be to add a field to our 'operating-system'
record that explicitly specifies a total mapping from user/group names
to UIDs/GIDs. It could either be a procedure (to support Danny's
hashing approach with its nice properties) or possibly also an alist for
convenience. If any entries were missing, it would raise an error.
One risk to this approach is that users could accidentally make a mess
of their system if they made a mistake while changing that field.
What do you think?
Thanks,
Mark
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 15 Apr 2021 14:25:02 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Thu Apr 15 10:25:02 2021 Received: from localhost ([127.0.0.1]:38826 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lX2vW-0002cb-19 for submit <at> debbugs.gnu.org; Thu, 15 Apr 2021 10:25:02 -0400 Received: from eggs.gnu.org ([209.51.188.92]:49524) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <ludo@HIDDEN>) id 1lX2vT-0002cD-7J for 36508 <at> debbugs.gnu.org; Thu, 15 Apr 2021 10:25:00 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:37295) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <ludo@HIDDEN>) id 1lX2vN-0000ou-4j; Thu, 15 Apr 2021 10:24:53 -0400 Received: from [2a01:e0a:1d:7270:af76:b9b:ca24:c465] (port=37672 helo=ribbon) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <ludo@HIDDEN>) id 1lX2vM-0005ij-L9; Thu, 15 Apr 2021 10:24:52 -0400 From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN> To: Brendan Tildesley <btild@HIDDEN> Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service References: <20190705083620.lbzu7a33awbymh3d@cf0> <1576552162.14721.1618320275616@HIDDEN> <87czuxsya5.fsf@HIDDEN> <875z0pgnqn.fsf@HIDDEN> <262720830.30369.1618402863721@HIDDEN> X-URL: http://www.fdn.fr/~lcourtes/ X-Revolutionary-Date: 26 Germinal an 229 de la =?utf-8?Q?R=C3=A9volution?= X-PGP-Key-ID: 0x090B11993D9AEBB5 X-PGP-Key: http://www.fdn.fr/~lcourtes/ludovic.asc X-PGP-Fingerprint: 3CE4 6455 8A84 FDC6 9DB4 0CFB 090B 1199 3D9A EBB5 X-OS: x86_64-pc-linux-gnu Date: Thu, 15 Apr 2021 16:24:51 +0200 In-Reply-To: <262720830.30369.1618402863721@HIDDEN> (Brendan Tildesley's message of "Wed, 14 Apr 2021 14:21:03 +0200 (CEST)") Message-ID: <87o8ef8w24.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: Mark H Weaver <mhw@HIDDEN>, 36508 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) Hi, Brendan Tildesley <btild@HIDDEN> skribis: >> On 04/14/2021 12:32 PM Ludovic Court=C3=A8s <ludo@HIDDEN> wrote: [...] >> The patch Brendan posted LGTM (though I=E2=80=99m surprised the director= y itself >> can have the right UID/GID while files inside it don=E2=80=99t; perhaps = this was >> made possible by 2161820ebbbab62a5ce76c9101ebaec54dc61586, which chowns >> the home directory unconditionally.) >>=20 >> Note that there are other places, in addition to GDM, where we >> forcefully reset the UID/GID of the home directory (e.g., for the >> =E2=80=98knot-resolver=E2=80=99 service.) >>=20 >> My preferred solution to this would be to unconditionally chown -R home >> directories upon activation (for efficiency, it would be best if we >> could do that if and only if the home directory itself has wrong >> ownership). Thoughts? >>=20 > I'm confused. It sounds like you're suggesting to add the very IF conditi= on that my > patch removes from %gdm-activation in order to fix the problem. I=E2=80=99d like to understand why the =E2=80=98if=E2=80=99 the patch remov= es was problematic. I think it relates to the commit above, but that needs more investigation. Ludo=E2=80=99.
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 14 Apr 2021 12:21:19 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Apr 14 08:21:19 2021 Received: from localhost ([127.0.0.1]:33860 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lWeWE-0005xC-SE for submit <at> debbugs.gnu.org; Wed, 14 Apr 2021 08:21:19 -0400 Received: from mout-p-101.mailbox.org ([80.241.56.151]:24040) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <btild@HIDDEN>) id 1lWeWC-0005wu-MG for 36508 <at> debbugs.gnu.org; Wed, 14 Apr 2021 08:21:18 -0400 Received: from smtp1.mailbox.org (smtp1.mailbox.org [IPv6:2001:67c:2050:105:465:1:1:0]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-384) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-101.mailbox.org (Postfix) with ESMTPS id 4FL1m6653DzQjwf; Wed, 14 Apr 2021 14:21:10 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mailbox.org; h= content-transfer-encoding:content-type:content-type:mime-version :subject:subject:references:in-reply-to:message-id:from:from :date:date:received; s=mail20150812; t=1618402864; bh=us9OXY5O5p GpfHLemJ5PLTjoywNrQkvn+AAnhigvAzs=; b=VAECrUpRBWVeYUy/WTvdZ/sEZm R4kkZqXlUhHtVc+0HgfFpcA4pwn0+7qVMMKqUFdZhz7L5DOAAAe+TiojnoXuFJTv Xzy6v1Sz7Sm4LVvQG78qke11RQSSacWSAzsWQRYCt9IjCsyJ3Ngk079wRmRKqAmP q1g7X/lJVdLwoG+BXlxfmGpsHiCUc2tL1YJl1wc6ASMbJMNMZu/emrcf/7tNcJZ4 MuU5a27wPP9Kuuabw/4GqwXb3T7wYhZ8D4tzpRQPAF88btP7bROrzqC33pz8mQ4W 5myz7WjjIeuCIBSco5zb2vWPiyjp16xqXqyUcYvakhwkHSzidjz9/EBktcpQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1618402869; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=q69mD9LGTrkxrzfmEZzwft414MS47zJTwr+PDEiit4Q=; b=fEZkH2tKz68kdsWqzjpg/f2305CvzkAlyGvpH5E9Gq8+qXO/ZhhARB8CKWtXPJHyBBJ9x4 Ii9BD6Yy8acxvonXm9jbP8+CxLUrwxws7GufuqxE5Eyw6XsqdpvnfvWv2h6XPpuF/hLQuP XvB8KlXy7zUIpKevQQm0FJDNtzpkDz8tD2kNS7EIjzTWx0jqTQOp76kob+cwItv75bpe55 icfoWhXdGWL+IIK/cfoVoBHdknOiqTLNlj+esxuklGwyUlXRIsaWLcPFLi91UgymAxg6lu KrwCLZs39ZrpB7Z7wezMy68/AQ0nH7FJh8ZbEDoBMzmPc1gFTv8cASihCmINSg== X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp1.mailbox.org ([80.241.60.240]) by spamfilter06.heinlein-hosting.de (spamfilter06.heinlein-hosting.de [80.241.56.125]) (amavisd-new, port 10030) with ESMTP id F7lSshsIBeZ3; Wed, 14 Apr 2021 14:21:04 +0200 (CEST) Date: Wed, 14 Apr 2021 14:21:03 +0200 (CEST) From: Brendan Tildesley <btild@HIDDEN> To: 36508 <at> debbugs.gnu.org Message-ID: <262720830.30369.1618402863721@HIDDEN> In-Reply-To: <875z0pgnqn.fsf@HIDDEN> References: <20190705083620.lbzu7a33awbymh3d@cf0> <1576552162.14721.1618320275616@HIDDEN> <87czuxsya5.fsf@HIDDEN> <875z0pgnqn.fsf@HIDDEN> Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Priority: 3 Importance: Normal X-MBO-SPAM-Probability: X-Rspamd-Score: -6.13 / 15.00 / 15.00 X-Rspamd-Queue-Id: BE85217CF X-Rspamd-UID: 8bef7e X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: Mark H Weaver <mhw@HIDDEN>, =?UTF-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) > On 04/14/2021 12:32 PM Ludovic Court=C3=A8s <ludo@HIDDEN> wrote: >=20 > =20 > Hi Mark, >=20 > Mark H Weaver <mhw@HIDDEN> skribis: >=20 > > Brendan Tildesley via Bug reports for GNU Guix <bug-guix@HIDDEN> > > writes: > > > >> I recently encountered what is likely the same bug. The directory /var= /lib/gdm > >> had the correct permissions gdm:gdm, but all the files inside had some= thing like > >> 973:gdm > > > > The underlying problem here, which I've also experienced, is that if yo= u > > reconfigure your system with fewer users/groups, and then later add > > those users/groups back, there is no guarantee that they will be > > assigned the same UIDs and GIDs. >=20 > Yes. >=20 > The patch Brendan posted LGTM (though I=E2=80=99m surprised the directory= itself > can have the right UID/GID while files inside it don=E2=80=99t; perhaps t= his was > made possible by 2161820ebbbab62a5ce76c9101ebaec54dc61586, which chowns > the home directory unconditionally.) >=20 > Note that there are other places, in addition to GDM, where we > forcefully reset the UID/GID of the home directory (e.g., for the > =E2=80=98knot-resolver=E2=80=99 service.) >=20 > My preferred solution to this would be to unconditionally chown -R home > directories upon activation (for efficiency, it would be best if we > could do that if and only if the home directory itself has wrong > ownership). Thoughts? >=20 I'm confused. It sounds like you're suggesting to add the very IF condition= that my patch removes from %gdm-activation in order to fix the problem.
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 14 Apr 2021 10:32:59 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Apr 14 06:32:59 2021 Received: from localhost ([127.0.0.1]:33669 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lWcpP-0000w2-EF for submit <at> debbugs.gnu.org; Wed, 14 Apr 2021 06:32:59 -0400 Received: from eggs.gnu.org ([209.51.188.92]:43136) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <ludo@HIDDEN>) id 1lWcpN-0000vp-F2 for 36508 <at> debbugs.gnu.org; Wed, 14 Apr 2021 06:32:57 -0400 Received: from fencepost.gnu.org ([2001:470:142:3::e]:40035) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from <ludo@HIDDEN>) id 1lWcpG-0007E9-Nq; Wed, 14 Apr 2021 06:32:51 -0400 Received: from [2a01:e0a:1d:7270:af76:b9b:ca24:c465] (port=34782 helo=ribbon) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from <ludo@HIDDEN>) id 1lWcpG-0000TX-9X; Wed, 14 Apr 2021 06:32:50 -0400 From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN> To: Mark H Weaver <mhw@HIDDEN> Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service References: <20190705083620.lbzu7a33awbymh3d@cf0> <1576552162.14721.1618320275616@HIDDEN> <87czuxsya5.fsf@HIDDEN> X-URL: http://www.fdn.fr/~lcourtes/ X-Revolutionary-Date: 25 Germinal an 229 de la =?utf-8?Q?R=C3=A9volution?= X-PGP-Key-ID: 0x090B11993D9AEBB5 X-PGP-Key: http://www.fdn.fr/~lcourtes/ludovic.asc X-PGP-Fingerprint: 3CE4 6455 8A84 FDC6 9DB4 0CFB 090B 1199 3D9A EBB5 X-OS: x86_64-pc-linux-gnu Date: Wed, 14 Apr 2021 12:32:48 +0200 In-Reply-To: <87czuxsya5.fsf@HIDDEN> (Mark H. Weaver's message of "Tue, 13 Apr 2021 16:51:35 -0400") Message-ID: <875z0pgnqn.fsf@HIDDEN> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: Brendan Tildesley <btild@HIDDEN>, 36508 <at> debbugs.gnu.org X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) Hi Mark, Mark H Weaver <mhw@HIDDEN> skribis: > Brendan Tildesley via Bug reports for GNU Guix <bug-guix@HIDDEN> > writes: > >> I recently encountered what is likely the same bug. The directory /var/l= ib/gdm >> had the correct permissions gdm:gdm, but all the files inside had someth= ing like >> 973:gdm > > The underlying problem here, which I've also experienced, is that if you > reconfigure your system with fewer users/groups, and then later add > those users/groups back, there is no guarantee that they will be > assigned the same UIDs and GIDs. Yes. The patch Brendan posted LGTM (though I=E2=80=99m surprised the directory i= tself can have the right UID/GID while files inside it don=E2=80=99t; perhaps thi= s was made possible by 2161820ebbbab62a5ce76c9101ebaec54dc61586, which chowns the home directory unconditionally.) Note that there are other places, in addition to GDM, where we forcefully reset the UID/GID of the home directory (e.g., for the =E2=80=98knot-resolver=E2=80=99 service.) My preferred solution to this would be to unconditionally chown -R home directories upon activation (for efficiency, it would be best if we could do that if and only if the home directory itself has wrong ownership). Thoughts? systemd-homed does something like that. The intuition here is that UIDs/GIDs are implementation details that should get out of the way. > There's some discussion of this issue at <https://bugs.gnu.org/44944>, > although I'm not sure that Danny's suggested solution is practical. > > Here's one idea: when activating a system, *never* delete users or > groups if files still exist that are owned by those users/groups. > Checking all filesystems would likely be too expensive, but perhaps it > would be sufficient to check certain directories such as /var, /etc, and > possibly the top directory of /home. How would you determine which directories to look at though? What if we miss an important one? Note that the ID allocation strategy in (gnu build accounts) ensures UIDs/GIDs aren=E2=80=99t reused right away (same strategy as implemented by Shadow, etc.). So if you remove =E2=80=9Cbob=E2=80=9D, then add =E2=80=9Ca= lice=E2=80=9D, =E2=80=9Calice=E2=80=9D won=E2=80=99t be able to access the left-behind /home/bob because it has a different UID. Ludo=E2=80=99.
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 14 Apr 2021 04:32:07 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Wed Apr 14 00:32:07 2021 Received: from localhost ([127.0.0.1]:33119 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lWXCB-0008A4-8p for submit <at> debbugs.gnu.org; Wed, 14 Apr 2021 00:32:07 -0400 Received: from mout-p-102.mailbox.org ([80.241.56.152]:15662) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <btild@HIDDEN>) id 1lWXC9-00089V-1j for 36508 <at> debbugs.gnu.org; Wed, 14 Apr 2021 00:32:06 -0400 Received: from smtp1.mailbox.org (smtp1.mailbox.org [IPv6:2001:67c:2050:105:465:1:1:0]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-384) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-102.mailbox.org (Postfix) with ESMTPS id 4FKqLk5FWMzQk1B; Wed, 14 Apr 2021 06:31:58 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mailbox.org; h= content-transfer-encoding:content-type:content-type:mime-version :subject:subject:references:in-reply-to:message-id:from:from :date:date:received; s=mail20150812; t=1618374714; bh=ouPL1qs6om xiQMs7gkF+Ue3RkqqmKGDxWSkqSIO7ZNQ=; b=eAp9VdEkykKOE+HGfgoKQBjJhx yryIWbJ1CtU6hG9hIAsb93f/z8RRllTxiP90gTGu81zyNPiAbixre2toJBdudC5A 3Lcvl9QPSmFJZbhjGgvyuWpm5KftRF+bof4C18tapXnbMKE04B4sX0dj+7Bn4IO2 2IE+2CAe/2YoLHfgbFyGXJFeI9L3d0cIZPhA6jJB4828rZSPimQftcKghTpklgXf XqGPBAFe6f5Av10CCe7pAQ8iffyoubgDvlciC8x4xYrk43FyIflvB7myuFs9J3O4 Rxrke7p2NlGZ9Vy5ItX2AK0Bl18F5N84TLmqYViLpcP4INqHyKrvbDMgsrwQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1618374716; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=C62iV6IxQGLQIxbZx1DNdC1AUs0Vor4kHPo/eDxfr2M=; b=XGv7labxwrvcBCvki7nr1izMqCQMd1JxqjqEmfPSMSXirRGd6+74NGoKdY09bkDhwgEoyM 0u++AkanPW/qQK6/uKLvlQtMzNV+cgoYWzGcQ4ll8yMXIjZw4Dmind4mUb/iKr7AjXjcMF frMhzB2AsNZwdHc8oJGHXaPJufOzaLwfNEyrbcWeTnjpWNTTZlJlycta51yhxLyXkikwTJ uWZN/zyXuQyouYdajTcS/3DcROF/hKp5O+hBwJt7Bv5iEli4dZMZIkOK/RAgVT+Fyzw3tL VjeuLMfOQtx3fki8jhLAZYzFTCTa98p8GFmOUyNik3dPj6tw99LxapSCOFa5IQ== X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp1.mailbox.org ([80.241.60.240]) by spamfilter04.heinlein-hosting.de (spamfilter04.heinlein-hosting.de [80.241.56.122]) (amavisd-new, port 10030) with ESMTP id fyRO9kQPTyV9; Wed, 14 Apr 2021 06:31:54 +0200 (CEST) Date: Wed, 14 Apr 2021 06:31:54 +0200 (CEST) From: Brendan Tildesley <btild@HIDDEN> To: 36508 <at> debbugs.gnu.org Message-ID: <461701204.22088.1618374714507@HIDDEN> In-Reply-To: <87czuxsya5.fsf@HIDDEN> References: <20190705083620.lbzu7a33awbymh3d@cf0> <1576552162.14721.1618320275616@HIDDEN> <87czuxsya5.fsf@HIDDEN> Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Priority: 3 Importance: Normal X-MBO-SPAM-Probability: X-Rspamd-Score: -6.44 / 15.00 / 15.00 X-Rspamd-Queue-Id: 5CDF017CC X-Rspamd-UID: 553017 X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: Mark H Weaver <mhw@HIDDEN>, =?UTF-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) > On 04/13/2021 10:51 PM Mark H Weaver <mhw@HIDDEN> wrote: > > > Hi Brendan, > > Brendan Tildesley via Bug reports for GNU Guix <bug-guix@HIDDEN> > writes: > > > I recently encountered what is likely the same bug. The directory /var/lib/gdm > > had the correct permissions gdm:gdm, but all the files inside had something like > > 973:gdm > > The underlying problem here, which I've also experienced, is that if you > reconfigure your system with fewer users/groups, and then later add > those users/groups back, there is no guarantee that they will be > assigned the same UIDs and GIDs. > > This problem is made much worse by the fact that files may be left > around, e.g. in /var, with the old UIDs and GIDs. > > In your case, I guess that the 'gdm' user was previously assigned UID > 973, but now it has been given a different UID. > > In my case, after reconfiguring to a minimal system and later switching > back to a full GNOME-based desktop system, I found that many files and > directories in /var had the wrong owner or group. Here's what I saw > before I cleaned things up: > > --8<---------------cut here---------------start------------->8--- > root@jojen ~# ls -l /var/lib/ > total 4 > drwxr-xr-x 1 colord colord 40 Mar 28 2017 colord > drwx------ 1 995 978 56 Sep 3 02:10 gdm > drwx------ 1 root root 30400 Dec 25 01:55 NetworkManager > -rw------- 1 root root 512 Dec 25 01:35 random-seed > drwxr-xr-x 1 colord colord 164 Dec 28 2017 sddm > drwx------ 1 tor tor 178 Dec 19 21:28 tor > drwx------ 1 root root 20 Sep 5 01:32 udisks2 > drwxr-xr-x 1 root root 274 Dec 25 01:55 upower > drwxr-xr-x 1 root root 86 Mar 28 2017 wicd > root@jojen ~# ls -la /var/lib/gdm/ > total 4 > drwx------ 1 995 978 56 Sep 3 02:10 . > drwxr-xr-x 1 root root 750 Dec 25 01:59 .. > drwxr-xr-x 1 994 colord 64 Sep 3 02:10 .cache > drwx------ 1 994 colord 54 Sep 3 02:10 .config > -rw------- 1 994 colord 16 Sep 3 02:10 .esd_auth > drwxr-xr-x 1 994 colord 10 Sep 3 02:10 .local > root@jojen ~# > --8<---------------cut here---------------end--------------->8--- > > Given the fact that existing files and directories in /var can > *effectively* have their ownership changed, I think that this issue > could be a security risk. Yes and they could change for any reason under the sun, and so we have no choice but to set them right on service activation. Guix system rollbacks should be a supported feature of Guix, not just a gimmick that falls out of its design. It should be that a Guix user could leave their system for 5 years, and then do a guix pull; guix system reconfigure in the year 2026. Perhaps at that time the new system will break, and then its desirable that they can rollback to the previous generation. So what fixes we put in to Guix services today need to consider not just how files could have changed in the past, but how they might change in breaking ways in the future, within reason. I don't know off the top of my head of any way that can be done other than to have chmod -R gdm:gdm /var/lib/gdm always executed. > > There's some discussion of this issue at <https://bugs.gnu.org/44944>, > although I'm not sure that Danny's suggested solution is practical. > > Here's one idea: when activating a system, *never* delete users or > groups if files still exist that are owned by those users/groups. > Checking all filesystems would likely be too expensive, but perhaps it > would be sufficient to check certain directories such as /var, /etc, and > possibly the top directory of /home. > > What do you think Wouldn't that imply that uids could be randomly different on different systems with the same configuration, and then remain statically different permanently? We want as little randomness and moving parts as possible. It's yet another way the system is not actually Functional, but has state. Seems this bug spans 3 or so different bug reports. In http://issues.guix.gnu.org/45571 I commented that Nix uses hard coded id's, sorta like how ports are allocated for a purpose: https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/misc/ids.nix Perhaps you are thinking of other kinds of security issues that could be caused that I'm not thinking of. In that case maybe Nix devs have already made the best choice by making them static? ... After all, if the permissions can change, then it is possible another user could actually modify the contents of /var/lib/gdm its self, thereby infecting other users, if for some reason that other malicious user gets allocated that ID. That further points towards static ID's like Nix has as a solution.
bug-guix@HIDDEN:bug#36508; Package guix.
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From: Mark H Weaver <mhw@HIDDEN>
To: Brendan Tildesley <btild@HIDDEN>, 36508 <at> debbugs.gnu.org
Subject: Re: bug#36508: GDM files have incorrect owner after temporarily
removing service
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Hi Brendan,
Brendan Tildesley via Bug reports for GNU Guix <bug-guix@HIDDEN>
writes:
> I recently encountered what is likely the same bug. The directory /var/lib/gdm
> had the correct permissions gdm:gdm, but all the files inside had something like
> 973:gdm
The underlying problem here, which I've also experienced, is that if you
reconfigure your system with fewer users/groups, and then later add
those users/groups back, there is no guarantee that they will be
assigned the same UIDs and GIDs.
This problem is made much worse by the fact that files may be left
around, e.g. in /var, with the old UIDs and GIDs.
In your case, I guess that the 'gdm' user was previously assigned UID
973, but now it has been given a different UID.
In my case, after reconfiguring to a minimal system and later switching
back to a full GNOME-based desktop system, I found that many files and
directories in /var had the wrong owner or group. Here's what I saw
before I cleaned things up:
--8<---------------cut here---------------start------------->8---
root@jojen ~# ls -l /var/lib/
total 4
drwxr-xr-x 1 colord colord 40 Mar 28 2017 colord
drwx------ 1 995 978 56 Sep 3 02:10 gdm
drwx------ 1 root root 30400 Dec 25 01:55 NetworkManager
-rw------- 1 root root 512 Dec 25 01:35 random-seed
drwxr-xr-x 1 colord colord 164 Dec 28 2017 sddm
drwx------ 1 tor tor 178 Dec 19 21:28 tor
drwx------ 1 root root 20 Sep 5 01:32 udisks2
drwxr-xr-x 1 root root 274 Dec 25 01:55 upower
drwxr-xr-x 1 root root 86 Mar 28 2017 wicd
root@jojen ~# ls -la /var/lib/gdm/
total 4
drwx------ 1 995 978 56 Sep 3 02:10 .
drwxr-xr-x 1 root root 750 Dec 25 01:59 ..
drwxr-xr-x 1 994 colord 64 Sep 3 02:10 .cache
drwx------ 1 994 colord 54 Sep 3 02:10 .config
-rw------- 1 994 colord 16 Sep 3 02:10 .esd_auth
drwxr-xr-x 1 994 colord 10 Sep 3 02:10 .local
root@jojen ~#
--8<---------------cut here---------------end--------------->8---
Given the fact that existing files and directories in /var can
*effectively* have their ownership changed, I think that this issue
could be a security risk.
There's some discussion of this issue at <https://bugs.gnu.org/44944>,
although I'm not sure that Danny's suggested solution is practical.
Here's one idea: when activating a system, *never* delete users or
groups if files still exist that are owned by those users/groups.
Checking all filesystems would likely be too expensive, but perhaps it
would be sufficient to check certain directories such as /var, /etc, and
possibly the top directory of /home.
What do you think?
Mark
bug-guix@HIDDEN:bug#36508; Package guix.
Full text available.Received: (at 36508) by debbugs.gnu.org; 13 Apr 2021 13:24:50 +0000 From debbugs-submit-bounces <at> debbugs.gnu.org Tue Apr 13 09:24:50 2021 Received: from localhost ([127.0.0.1]:59318 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <debbugs-submit-bounces <at> debbugs.gnu.org>) id 1lWJ29-0004Ad-Mh for submit <at> debbugs.gnu.org; Tue, 13 Apr 2021 09:24:50 -0400 Received: from mout-p-201.mailbox.org ([80.241.56.171]:18516) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from <btild@HIDDEN>) id 1lWJ28-0004AL-Nc for 36508 <at> debbugs.gnu.org; Tue, 13 Apr 2021 09:24:49 -0400 Received: from smtp2.mailbox.org (smtp2.mailbox.org [80.241.60.241]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-384) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-201.mailbox.org (Postfix) with ESMTPS id 4FKRCt4D9fzQjy8; Tue, 13 Apr 2021 15:24:42 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mailbox.org; h= content-type:content-type:mime-version:subject:subject :message-id:from:from:date:date:received; s=mail20150812; t= 1618320275; bh=vGJi47T/LMs4Dq1TDG334T1VqMJQEvuDHoTf9xbm4Es=; b=s z4AjoN2cm30nTVBOi9TKwlh7UxRyEVd1UKX/veUqXzwj1cFQtYbeLwsuvo4XdHde UJnJGol21mgnvWwcpot8vqGgMKo/TJ94AfyuNccDTWKG6sVlMer9gq/Z1XhAEJft QVE8VB5TpINxKb7qGdZ4TaB0pJPwZM3wYKB7QhSy1MWhaEYlzQUw7AkPpDS+GnGN et9+kZ1SldJ8FDvUHZ35VIOUIOLjf8M4Vjh+HLDiHKgFhYYH/KrjI/NRtOR+a6J3 X0NuHJBD/zx3CgPPi3n7Q+8ebuxk6wOEfOYwsxEAh4yPHTvTcsJ8ettgtO3DN41M ymNiIArhWaXeuwQ+BsXVA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1618320280; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type; bh=rLiK3gLIJ8/HiIhETWjvw3yfbb0+bZCdmxVmS1tNyss=; b=XeDjmT3S454yytMwJBFE0Odjzj134EtpptfxQZfGP6CLu612oqU36s2EiCqselO+7QOdY6 XP2uEG7naQQBP787VyBUOkj82uVoONLEiF9Y/Kgqx71bx7b5tOdvuYEo+P2MxC+b+OP9JE 5kSf/kflyaiqkMN2jWT5+U3GiKp15ChyzmuJ+pPE28AanxrwWuCMl5E46cFM/JVbTP76DN osyJPbMS2QNeUXPbxrz17vSrMN2Mb9ZYPdMhYDzT0syXy+0yt67wES8pDxuYilTiFYsGET 2euhZ4iAiXVUYB95PdtO8uxT3Csq7Jtp8Hh8B+xeFQtT4T7o9A+9f/iWngiGrA== X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp2.mailbox.org ([80.241.60.241]) by spamfilter04.heinlein-hosting.de (spamfilter04.heinlein-hosting.de [80.241.56.122]) (amavisd-new, port 10030) with ESMTP id yMGIi3yscDoP; Tue, 13 Apr 2021 15:24:35 +0200 (CEST) Date: Tue, 13 Apr 2021 15:24:35 +0200 (CEST) From: Brendan Tildesley <btild@HIDDEN> To: "36508 <at> debbugs.gnu.org" <36508 <at> debbugs.gnu.org> Message-ID: <1576552162.14721.1618320275616@HIDDEN> Subject: GDM files have incorrect owner after temporarily removing service MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_14719_1225470587.1618320275370" X-Priority: 3 Importance: Normal X-MBO-SPAM-Probability: * X-Rspamd-Score: 1.33 / 15.00 / 15.00 X-Rspamd-Queue-Id: 47E131811 X-Rspamd-UID: 84e62a X-Spam-Score: -0.7 (/) X-Debbugs-Envelope-To: 36508 Cc: =?UTF-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN> X-BeenThere: debbugs-submit <at> debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: <debbugs-submit.debbugs.gnu.org> List-Unsubscribe: <https://debbugs.gnu.org/cgi-bin/mailman/options/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=unsubscribe> List-Archive: <https://debbugs.gnu.org/cgi-bin/mailman/private/debbugs-submit/> List-Post: <mailto:debbugs-submit <at> debbugs.gnu.org> List-Help: <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=help> List-Subscribe: <https://debbugs.gnu.org/cgi-bin/mailman/listinfo/debbugs-submit>, <mailto:debbugs-submit-request <at> debbugs.gnu.org?subject=subscribe> Errors-To: debbugs-submit-bounces <at> debbugs.gnu.org Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org> X-Spam-Score: -1.7 (-) ------=_Part_14719_1225470587.1618320275370 Content-Type: multipart/alternative; boundary="----=_Part_14720_877439344.1618320275371" ------=_Part_14720_877439344.1618320275371 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit I recently encountered what is likely the same bug. The directory /var/lib/gdm had the correct permissions gdm:gdm, but all the files inside had something like 973:gdm a43e9157ef479e94c19951cc9d228cf153bf78ee is supposed to fix this (duplicate bug 37423) but it only checks the permissions of /var/lib/gdm/ itself. Not all of the files in it. This explains why in my case it failed to fix the permissions, because the directory was gdm:gdm. How it got that way I don't know, and infact it doesn't really matter. The directory is mutable, and thus can theoretically be changed for any number of reasons. Therefore if we wish for Guix to be robust with it's Functional design, and have meaningful rollbacks, we perhaps have no choice but to assert the required invariants like these on mutable files. A better solution may be to make it fully chown -R on reconfigure, but not each time on boot? I've attached an untested patch with a suggested solution of making %gdm-activation operate every single time, instead of just after checking /var/lib/gdm. ------=_Part_14720_877439344.1618320275371 MIME-Version: 1.0 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 7bit <!doctype html> <html> <head> <meta charset="UTF-8"> </head> <body> <div style="" class="default-style"> I recently encountered what is likely the same bug. The directory /var/lib/gdm <br>had the correct permissions gdm:gdm, but all the files inside had something like <br>973:gdm <br> <br>a43e9157ef479e94c19951cc9d228cf153bf78ee is supposed to fix this (duplicate bug <br>37423) but it only checks the permissions of /var/lib/gdm/ itself. Not all of <br>the files in it. This explains why in my case it failed to fix the permissions, <br>because the directory was gdm:gdm. How it got that way I don't know, and infact </div> <div style="" class="default-style"> it doesn't really matter. The directory is mutable, and thus can theoretically be </div> <div style="" class="default-style"> changed for any number of reasons. Therefore if we wish for Guix to be robust </div> <div style="" class="default-style"> with it's Functional design, and have meaningful rollbacks, we perhaps have no </div> <div style="" class="default-style"> choice but to assert the required invariants like these on mutable files. </div> <div style="" class="default-style"> <br> </div> <div style="" class="default-style"> A better solution may be to make it fully chown -R on reconfigure, but not each time </div> <div style="" class="default-style"> on boot? <br> <br>I've attached an untested patch with a suggested solution of making <br>%gdm-activation operate every single time, instead of just after checking <br>/var/lib/gdm. <br> <br> <br> </div> </body> </html> ------=_Part_14720_877439344.1618320275371-- ------=_Part_14719_1225470587.1618320275370 Content-Type: text/x-patch; charset=ISO-8859-1; name=0001-services-gdm-Correctly-set-ownership-on-var-lib-gdm.patch Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename=0001-services-gdm-Correctly-set-ownership-on-var-lib-gdm.patch X-Part-Id: c69ffe53ac4e4a34a93d63e62b794a98 RnJvbSAzMWNiNmRiZDc1NmFmNjk1YmQ2YTFmNGQ0Yzg5YjQyMzY3YjEzMzA3IE1vbiBTZXAgMTcg MDA6MDA6MDAgMjAwMQpGcm9tOiBCcmVuZGFuIFRpbGRlc2xleSA8bWFpbEBicmVuZGFuLnNjb3Q+ CkRhdGU6IFR1ZSwgMTMgQXByIDIwMjEgMjM6MDQ6MjggKzEwMDAKU3ViamVjdDogW1BBVENIXSBz ZXJ2aWNlczogZ2RtOiBDb3JyZWN0bHkgc2V0IG93bmVyc2hpcCBvbiAvdmFyL2xpYi9nZG0uCgoq IGdudS9zZXJ2aWNlcy94b3JnLnNjbSAoJWdkbS1hY3RpdmF0aW9uKTogQWx3YXlzIGNob3duIC92 YXIvbGliL2dkbSwKaW5zdGVhZCBvZiBvbmx5IHdoZW4gaXQgYXBwZWFycyB0byBiZSBjb3JyZWN0 LCBiZWNhdXNlIGl0J3Mgc3RpbGwKcG9zc2libGUgdGhlIGZpbGVzIGluc2lkZSBjb3VsZCBiZSB3 cm9uZyBhbmQgYnJlYWsgR0RNLiBJIGVuY291bnRlcmVkCnRoaXMgb25jZTogaHR0cHM6Ly9pc3N1 ZXMuZ3VpeC5nbnUub3JnLzM2NTA4IC4KClBlcmhhcHMgaXQgaXMgd2l0aCBnb29kIGludGVudGlv bnMgdG8gdHJ5IG5vdCBydW5uaW5nIHRoaXMgY29kZSBldmVyeQpzaW5nbGUgdGltZSBvbiBib290 LCBidXQgd2hlbiBpdCBmYWlscywgdGhlIGNvbnNlcXVlbmNlIGlzIHRoYXQgR0RNIGNhbgpicmVh ayBub3QganVzdCBmb3IgdGhlIGN1cnJlbnQgcmV2aXNpb24sIGJ1dCBhbGwgcHJldmlvdXMgcm9s bGJhY2sKc3lzdGVtcyBpbiBHUlVCIHdpbGwgZmFpbCwgYW5kIHN1YnNlcXVlbnQgcmVjb25maWd1 cmUtaW5ncyBmYWlsCnRvby4gVGhhdCB0b3RhbGx5IGRlc3Ryb3lzIGEgZGVza3RvcCBzeXN0ZW0g YW5kIG91ciByb2xsYmFjawpmdW5jdGlvbmFsbHksIHdoaWNoIGlzIG11Y2ggbXVjaCB3b3JzZSEK LS0tCiBnbnUvc2VydmljZXMveG9yZy5zY20gfCAxNSArKysrKy0tLS0tLS0tLS0KIDEgZmlsZSBj aGFuZ2VkLCA1IGluc2VydGlvbnMoKyksIDEwIGRlbGV0aW9ucygtKQoKZGlmZiAtLWdpdCBhL2du dS9zZXJ2aWNlcy94b3JnLnNjbSBiL2dudS9zZXJ2aWNlcy94b3JnLnNjbQppbmRleCAxN2Q5ODNm ZjhkLi5hMjA2YzdjOTNhIDEwMDY0NAotLS0gYS9nbnUvc2VydmljZXMveG9yZy5zY20KKysrIGIv Z251L3NlcnZpY2VzL3hvcmcuc2NtCkBAIC04NjEsMTYgKzg2MSwxMSBAQCB0aGUgR05PTUUgZGVz a3RvcCBlbnZpcm9ubWVudC4iKQogCiAgICAgICAgIChsZXQqICgoZ2RtIChnZXRwd25hbSAiZ2Rt IikpCiAgICAgICAgICAgICAgICAodWlkIChwYXNzd2Q6dWlkIGdkbSkpCi0gICAgICAgICAgICAg ICAoZ2lkIChwYXNzd2Q6Z2lkIGdkbSkpCi0gICAgICAgICAgICAgICAoc3QgIChzdGF0ICIvdmFy L2xpYi9nZG0iICNmKSkpCi0gICAgICAgICAgOzsgUmVjdXJzZSBpbnRvIC92YXIvbGliL2dkbSBv bmx5IGlmIGl0IGhhcyB3cm9uZyBvd25lcnNoaXAuCi0gICAgICAgICAgKHdoZW4gKGFuZCBzdAot ICAgICAgICAgICAgICAgICAgICAgKG9yIChub3QgKD0gdWlkIChzdGF0OnVpZCBzdCkpKQotICAg ICAgICAgICAgICAgICAgICAgICAgIChub3QgKD0gZ2lkIChzdGF0OmdpZCBzdCkpKSkpCi0gICAg ICAgICAgICAoZm9yLWVhY2ggKGxhbWJkYSAoZmlsZSkKLSAgICAgICAgICAgICAgICAgICAgICAg IChjaG93biBmaWxlIHVpZCBnaWQpKQotICAgICAgICAgICAgICAgICAgICAgIChmaW5kLWZpbGVz ICIvdmFyL2xpYi9nZG0iCi0gICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgIzpkaXJl Y3Rvcmllcz8gI3QpKSkpKSkpCisgICAgICAgICAgICAgICAoZ2lkIChwYXNzd2Q6Z2lkIGdkbSkp KQorICAgICAgICAgIChmb3ItZWFjaCAobGFtYmRhIChmaWxlKQorICAgICAgICAgICAgICAgICAg ICAgIChjaG93biBmaWxlIHVpZCBnaWQpKQorICAgICAgICAgICAgICAgICAgICAoZmluZC1maWxl cyAiL3Zhci9saWIvZ2RtIgorICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAjOmRpcmVj dG9yaWVzPyAjdCkpKSkpKQogCiAoZGVmaW5lIGRidXMtZGFlbW9uLXdyYXBwZXIKICAgKHByb2dy YW0tZmlsZQotLSAKMi4zMS4xCgo= ------=_Part_14719_1225470587.1618320275370--
bug-guix@HIDDEN:bug#36508; Package guix.
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From: ison <ison@HIDDEN>
To: bug-guix@HIDDEN
Subject: GDM files have incorrect owner after temporarily replacing with SDDM
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After replacing GDM with SDDM in my Guix System config (to test Wayland) and
then reverting back to my old config and reconfiguring GDM would crash
(printing out around 500 lines about creating a seat)
I also tried rolling back to the generation I had before using SDDM and it would
still crash.
In both instances I also tried "herd restart xorg-server" but same problem.
I then checked the log file /var/log/gdm/greeter.log which had errors such as:
-------------------
Fatal server error:
(EE) Cannot open log file "/var/lib/gdm/.local/share/xorg/Xorg.pid-720.log"
-------------------
And then I could verify that files inside of /var/lib/gdm had incorrect
ownership of 9##:gdm
where 9## was some 3-digit number I can't remember now.
(note: the directory itself /var/lib/gdm still had correct ownership gdm:gdm)
I then manually fixed the ownership with:
chown -R gdm:gdm /var/lib/gdm
and GDM successfully came up without crashing.
The relevant portion of my config when I replaced GDM with SDDM was:
-------------------------------
(operating-system
...
(services
(cons*
...
(sddm-service
(sddm-configuration
(display-server "wayland")))
;; Return %desktop-services with GDM removed
(remove (lambda (service)
(eq? (service-kind service) gdm-service-type))
%desktop-services))))
-------------------------------
ison <ison@HIDDEN>:bug-guix@HIDDEN.
Full text available.bug-guix@HIDDEN:bug#36508; Package guix.
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