GNU bug report logs - #77232
[PATCH] Allow also to get attributes of the terminal line

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Werner Fink <werner <at> suse.de>
To: bug-gnu-emacs <at> gnu.org
Cc: Werner Fink <werner <at> suse.de>
Subject: [PATCH] Allow also to get attributes of the terminal line
Date: Mon, 24 Mar 2025 09:51:47 +0100

as well as support mmap(2) flag MAP_DROPPABLE to allow
zero memory under memory pressure on newer Linux systems.

Otherwise a `make -k check` fails here in our build environment
with newer kernels and with /dev/console as physical device.

Signed-off-by: Werner Fink <werner <at> suse.de>
---
 lib-src/seccomp-filter.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git lib-src/seccomp-filter.c lib-src/seccomp-filter.c
index d6421f0ebdb..4dda7d8f020 100644
--- lib-src/seccomp-filter.c
+++ lib-src/seccomp-filter.c
@@ -42,6 +42,9 @@ variants of those files that can be used to sandbox Emacs before
 #include <stdlib.h>
 #include <stdint.h>
 #include <stdio.h>
+/* glibc uses internal an other TCGETS ioctl for its
+   tcgetattr(3) call with its internal struct termios */
+#include <asm/termbits.h>
 #include <time.h>
 
 #include <asm/prctl.h>
@@ -64,6 +67,11 @@ variants of those files that can be used to sandbox Emacs before
 #define ARCH_CET_STATUS 0x3001
 #endif
 
+/* https://github.com/torvalds/linux/commit/9651fcedf7b92d3f7f1ab179e8ab55b85ee10fc1 */
+#ifndef MAP_DROPPABLE
+#define MAP_DROPPABLE 0x0
+#endif
+
 static ATTRIBUTE_FORMAT_PRINTF (2, 3) _Noreturn void
 fail (int error, const char *format, ...)
 {
@@ -187,7 +195,7 @@ main (int argc, char **argv)
            some versions of the dynamic loader still use it.  Also
            allow allocating thread stacks.  */
         SCMP_A3_32 (SCMP_CMP_MASKED_EQ,
-                    ~(MAP_SHARED | MAP_PRIVATE | MAP_FILE
+                    ~(MAP_SHARED | MAP_PRIVATE | MAP_FILE | MAP_DROPPABLE
                       | MAP_ANONYMOUS | MAP_FIXED | MAP_DENYWRITE
                       | MAP_STACK | MAP_NORESERVE),
                     0));
@@ -274,6 +282,11 @@ main (int argc, char **argv)
         SCMP_A0_32 (SCMP_CMP_EQ, STDIN_FILENO),
         SCMP_A1_32 (SCMP_CMP_EQ, TIOCGPGRP));
 
+  /* Allow `tcgetattr' call of glibc on physical terminal devices. */
+  RULE (SCMP_ACT_ALLOW, SCMP_SYS (ioctl),
+        SCMP_A0_32 (SCMP_CMP_EQ, STDERR_FILENO),
+        SCMP_A1_32 (SCMP_CMP_EQ, TCGETS));
+
   /* Allow reading (but not setting) file flags.  */
   RULE (SCMP_ACT_ALLOW, SCMP_SYS (fcntl),
         SCMP_A1_32 (SCMP_CMP_EQ, F_GETFL));
-- 
2.35.3

Message #8 received at 77232 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Werner Fink <werner <at> suse.de>, Philipp Stephani <p.stephani2 <at> gmail.com>,
 Philipp Stephani <phst <at> google.com>
Cc: 77232 <at> debbugs.gnu.org
Subject: Re: bug#77232: [PATCH] Allow also to get attributes of the terminal
 line
Date: Mon, 24 Mar 2025 14:42:02 +0200

> Cc: Werner Fink <werner <at> suse.de>
> From: Werner Fink <werner <at> suse.de>
> Date: Mon, 24 Mar 2025 09:51:47 +0100
> 
> as well as support mmap(2) flag MAP_DROPPABLE to allow
> zero memory under memory pressure on newer Linux systems.
> 
> Otherwise a `make -k check` fails here in our build environment
> with newer kernels and with /dev/console as physical device.
> 
> Signed-off-by: Werner Fink <werner <at> suse.de>

Thanks.

Philipp, any comments?

> ---
>  lib-src/seccomp-filter.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git lib-src/seccomp-filter.c lib-src/seccomp-filter.c
> index d6421f0ebdb..4dda7d8f020 100644
> --- lib-src/seccomp-filter.c
> +++ lib-src/seccomp-filter.c
> @@ -42,6 +42,9 @@ variants of those files that can be used to sandbox Emacs before
>  #include <stdlib.h>
>  #include <stdint.h>
>  #include <stdio.h>
> +/* glibc uses internal an other TCGETS ioctl for its
> +   tcgetattr(3) call with its internal struct termios */
> +#include <asm/termbits.h>
>  #include <time.h>
>  
>  #include <asm/prctl.h>
> @@ -64,6 +67,11 @@ variants of those files that can be used to sandbox Emacs before
>  #define ARCH_CET_STATUS 0x3001
>  #endif
>  
> +/* https://github.com/torvalds/linux/commit/9651fcedf7b92d3f7f1ab179e8ab55b85ee10fc1 */
> +#ifndef MAP_DROPPABLE
> +#define MAP_DROPPABLE 0x0
> +#endif
> +
>  static ATTRIBUTE_FORMAT_PRINTF (2, 3) _Noreturn void
>  fail (int error, const char *format, ...)
>  {
> @@ -187,7 +195,7 @@ main (int argc, char **argv)
>             some versions of the dynamic loader still use it.  Also
>             allow allocating thread stacks.  */
>          SCMP_A3_32 (SCMP_CMP_MASKED_EQ,
> -                    ~(MAP_SHARED | MAP_PRIVATE | MAP_FILE
> +                    ~(MAP_SHARED | MAP_PRIVATE | MAP_FILE | MAP_DROPPABLE
>                        | MAP_ANONYMOUS | MAP_FIXED | MAP_DENYWRITE
>                        | MAP_STACK | MAP_NORESERVE),
>                      0));
> @@ -274,6 +282,11 @@ main (int argc, char **argv)
>          SCMP_A0_32 (SCMP_CMP_EQ, STDIN_FILENO),
>          SCMP_A1_32 (SCMP_CMP_EQ, TIOCGPGRP));
>  
> +  /* Allow `tcgetattr' call of glibc on physical terminal devices. */
> +  RULE (SCMP_ACT_ALLOW, SCMP_SYS (ioctl),
> +        SCMP_A0_32 (SCMP_CMP_EQ, STDERR_FILENO),
> +        SCMP_A1_32 (SCMP_CMP_EQ, TCGETS));
> +
>    /* Allow reading (but not setting) file flags.  */
>    RULE (SCMP_ACT_ALLOW, SCMP_SYS (fcntl),
>          SCMP_A1_32 (SCMP_CMP_EQ, F_GETFL));
> -- 
> 2.35.3
> 
> 
> 
> 
> 

Message #11 received at 77232 <at> debbugs.gnu.org (full text, mbox):

From: Philipp Stephani <p.stephani2 <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Philipp Stephani <phst <at> google.com>, 77232 <at> debbugs.gnu.org,
 Werner Fink <werner <at> suse.de>
Subject: Re: bug#77232: [PATCH] Allow also to get attributes of the terminal
 line
Date: Tue, 25 Mar 2025 16:06:39 +0100

> Am 24.03.2025 um 13:42 schrieb Eli Zaretskii <eliz <at> gnu.org>:
> 
>> Cc: Werner Fink <werner <at> suse.de>
>> From: Werner Fink <werner <at> suse.de>
>> Date: Mon, 24 Mar 2025 09:51:47 +0100
>> 
>> as well as support mmap(2) flag MAP_DROPPABLE to allow
>> zero memory under memory pressure on newer Linux systems.
>> 
>> Otherwise a `make -k check` fails here in our build environment
>> with newer kernels and with /dev/console as physical device.
>> 
>> Signed-off-by: Werner Fink <werner <at> suse.de>
> 
> Thanks.
> 
> Philipp, any comments?
> 
>> ---
>> lib-src/seccomp-filter.c | 19 ++++++++++++++++++-
>> 1 file changed, 18 insertions(+), 1 deletion(-)
>> 
>> diff --git lib-src/seccomp-filter.c lib-src/seccomp-filter.c
>> index d6421f0ebdb..4dda7d8f020 100644
>> --- lib-src/seccomp-filter.c
>> +++ lib-src/seccomp-filter.c
>> @@ -42,6 +42,9 @@ variants of those files that can be used to sandbox Emacs before
>> #include <stdlib.h>
>> #include <stdint.h>
>> #include <stdio.h>
>> +/* glibc uses internal an other TCGETS ioctl for its
>> +   tcgetattr(3) call with its internal struct termios */
>> +#include <asm/termbits.h>
>> #include <time.h>
>> 
>> #include <asm/prctl.h>
>> @@ -64,6 +67,11 @@ variants of those files that can be used to sandbox Emacs before
>> #define ARCH_CET_STATUS 0x3001
>> #endif
>> 
>> +/* https://github.com/torvalds/linux/commit/9651fcedf7b92d3f7f1ab179e8ab55b85ee10fc1 */
>> +#ifndef MAP_DROPPABLE
>> +#define MAP_DROPPABLE 0x0

Shouldn't this be 0x08? At least that's how it's defined in mman.h.

>> +#endif
>> +
>> static ATTRIBUTE_FORMAT_PRINTF (2, 3) _Noreturn void
>> fail (int error, const char *format, ...)
>> {
>> @@ -187,7 +195,7 @@ main (int argc, char **argv)
>>            some versions of the dynamic loader still use it.  Also
>>            allow allocating thread stacks.  */
>>         SCMP_A3_32 (SCMP_CMP_MASKED_EQ,
>> -                    ~(MAP_SHARED | MAP_PRIVATE | MAP_FILE
>> +                    ~(MAP_SHARED | MAP_PRIVATE | MAP_FILE | MAP_DROPPABLE
>>                       | MAP_ANONYMOUS | MAP_FIXED | MAP_DENYWRITE
>>                       | MAP_STACK | MAP_NORESERVE),
>>                     0));
>> @@ -274,6 +282,11 @@ main (int argc, char **argv)
>>         SCMP_A0_32 (SCMP_CMP_EQ, STDIN_FILENO),
>>         SCMP_A1_32 (SCMP_CMP_EQ, TIOCGPGRP));
>> 
>> +  /* Allow `tcgetattr' call of glibc on physical terminal devices. */
>> +  RULE (SCMP_ACT_ALLOW, SCMP_SYS (ioctl),
>> +        SCMP_A0_32 (SCMP_CMP_EQ, STDERR_FILENO),
>> +        SCMP_A1_32 (SCMP_CMP_EQ, TCGETS));
>> +
>>   /* Allow reading (but not setting) file flags.  */
>>   RULE (SCMP_ACT_ALLOW, SCMP_SYS (fcntl),
>>         SCMP_A1_32 (SCMP_CMP_EQ, F_GETFL));
>> -- 
>> 2.35.3
>> 
>> 
>> 
>> 
>> 

Message #14 received at 77232 <at> debbugs.gnu.org (full text, mbox):

From: "Dr. Werner Fink" <werner <at> suse.de>
To: Philipp Stephani <p.stephani2 <at> gmail.com>
Cc: Philipp Stephani <phst <at> google.com>, 77232 <at> debbugs.gnu.org,
 Eli Zaretskii <eliz <at> gnu.org>
Subject: Re: bug#77232: [PATCH] Allow also to get attributes of the terminal
 line
Date: Tue, 25 Mar 2025 16:24:22 +0100

[Message part 1 (text/plain, inline)]

On 2025/03/25 16:06:39 +0100, Philipp Stephani wrote:
> >> #endif
> >> 
> >> +/* https://github.com/torvalds/linux/commit/9651fcedf7b92d3f7f1ab179e8ab55b85ee10fc1 */
> >> +#ifndef MAP_DROPPABLE
> >> +#define MAP_DROPPABLE 0x0
> 
> Shouldn't this be 0x08? At least that's how it's defined in mman.h.

If the kernel does not know (means header does not know) we should not
set an unknown flags as this will fail also (IMHO).
Only if older header files are used in combination with newer kernel
we would see the current behaviour.

Werner
-- 
  "Having a smoking section in a restaurant is like having
          a peeing section in a swimming pool." -- Edward Burr

[signature.asc (application/pgp-signature, inline)]

Message #17 received at 77232 <at> debbugs.gnu.org (full text, mbox):

From: Philipp Stephani <p.stephani2 <at> gmail.com>
To: "Dr. Werner Fink" <werner <at> suse.de>
Cc: 77232 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
Subject: Re: bug#77232: [PATCH] Allow also to get attributes of the terminal
 line
Date: Tue, 25 Mar 2025 17:22:22 +0100

> Am 25.03.2025 um 16:24 schrieb Dr. Werner Fink <werner <at> suse.de>:
> 
> On 2025/03/25 16:06:39 +0100, Philipp Stephani wrote:
>>>> #endif
>>>> 
>>>> +/* https://github.com/torvalds/linux/commit/9651fcedf7b92d3f7f1ab179e8ab55b85ee10fc1 */
>>>> +#ifndef MAP_DROPPABLE
>>>> +#define MAP_DROPPABLE 0x0
>> 
>> Shouldn't this be 0x08? At least that's how it's defined in mman.h.
> 
> If the kernel does not know (means header does not know) we should not
> set an unknown flags as this will fail also (IMHO).
> Only if older header files are used in combination with newer kernel
> we would see the current behaviour.

The code in question doesn't actually call mmap, it creates a syscall filter that tests whether any unknown flags are set.  Basically
  if ((flags & ~known_flags) != 0) abort();
So putting something into known_flags that might not be known to the kernel when Emacs is run is harmless.  In fact, it's beneficial for the case where the mman.h that's used when compiling seccomp-filter.c is older than the kernel that will be used to run Emacs.

Message #20 received at 77232 <at> debbugs.gnu.org (full text, mbox):

From: Björn Bidar <bjorn.bidar <at> thaodan.de>
To: Werner Fink <werner <at> suse.de>
Cc: 77232 <at> debbugs.gnu.org
Subject: Re: bug#77232: [PATCH] Allow also to get attributes of the terminal
 line
Date: Wed, 26 Mar 2025 18:00:59 +0200

Werner Fink <werner <at> suse.de> writes:

> as well as support mmap(2) flag MAP_DROPPABLE to allow
> zero memory under memory pressure on newer Linux systems.
>
> Otherwise a `make -k check` fails here in our build environment
> with newer kernels and with /dev/console as physical device.
>
> Signed-off-by: Werner Fink <werner <at> suse.de>
> ---
>  lib-src/seccomp-filter.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git lib-src/seccomp-filter.c lib-src/seccomp-filter.c
> index d6421f0ebdb..4dda7d8f020 100644
> --- lib-src/seccomp-filter.c
> +++ lib-src/seccomp-filter.c
> @@ -42,6 +42,9 @@ variants of those files that can be used to sandbox Emacs before
>  #include <stdlib.h>
>  #include <stdint.h>
>  #include <stdio.h>
> +/* glibc uses internal an other TCGETS ioctl for its
> +   tcgetattr(3) call with its internal struct termios */
> +#include <asm/termbits.h>
>  #include <time.h>
>
>  #include <asm/prctl.h>
> @@ -64,6 +67,11 @@ variants of those files that can be used to sandbox Emacs before
>  #define ARCH_CET_STATUS 0x3001
>  #endif
>
> +/*
> https://github.com/torvalds/linux/commit/9651fcedf7b92d3f7f1ab179e8ab55b85ee10fc1
> */

Nit pick could you link to kernel.org instead?

The replacement link would be:
https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9651fcedf7b92d3f7f1ab179e8ab55b85ee10fc1

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