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linux: Use fchmodat2 on fchmod for flags different than 0 (BZ 26401)

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Linux 6.6 (09da082b07bbae1c) added support for fchmodat2, which has
similar semantics as fchmodat with an extra flag argument.  This
allows fchmodat to implement AT_SYMLINK_NOFOLLOW and AT_EMPTY_PATH
without the need for procfs.

The syscall is registered on all architectures (with value of 452
except on alpha which is 562, commit 78252deb023cf087).

The tst-lchmod.c requires a small fix where fchmodat checks two
contradictory assertions ('(st.st_mode & 0777) == 2' and
'(st.st_mode & 0777) == 3').

Checked on x86_64-linux-gnu on a 6.6 kernel.

Reviewed-by: Florian Weimer <fweimer@redhat.com>
This commit is contained in:
Adhemerval Zanella
2023-09-28 13:56:21 -03:00
parent c52c2c32db
commit 65341f7bbe
3 changed files with 80 additions and 58 deletions
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8
sysdeps/unix/sysv/linux/kernel-features.h
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@@ -252,4 +252,12 @@
# define __ASSUME_CLONE3 0
#endif
/* The fchmodat2 system call was introduced across all architectures
in Linux 6.6. */
#if __LINUX_KERNEL_VERSION >= 0x060600
# define __ASSUME_FCHMODAT2 1
#else
# define __ASSUME_FCHMODAT2 0
#endif
#endif /* kernel-features.h */