Subject: Re: bug#77232: [PATCH] Allow also to get attributes of the terminal line

From: Philipp Stephani <[email-masked]>
Date: Tue, 25 Mar 2025 16:06:39 +0100

> Am 24.03.2025 um 13:42 schrieb Eli Zaretskii <[email-masked]>:
> 
>> Cc: Werner Fink <[email-masked]>
>> From: Werner Fink <[email-masked]>
>> 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 <[email-masked]>
> 
> 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
>> 
>> 
>> 
>> 
>>