Frantisek Sumsal
fb73687370
When --suppress-sync=yes was introduced in
4a4654e024 it filtered out openat2()
completely, as we can't check its "flags" argument because it's hidden
in an indirect struct. This was perfectly fine at that time, as
openat2() was quite new and software shipped with a fallback to
open()/openat() if the syscall wasn't present.
However, today the situation is different and an increasing number of
software is moving to openat2() without any fallback - tar [0] being the
most common one in the recent reports and workarounds, and attr recently
fixed a CVE by switching to openat2() [1] as well, to name a few.
Given that we already block all the sync-family syscalls and calling
openat2() with O_SYNC is relatively rare, let's just blanket-enable it
in the --suppress-sync=yes mode. This means that we might issue a
synchronous write when something calls openat2() with O_SYNC, but not
breaking the apps here feels like a reasonable trade-off, at least until
a better solution pops up.
Note that the same situation is in seccomp_restrict_sxid(), but allowing
the openat2() syscall there could actually have some security-related
implications under certain circumstances.
Resolves: #41868
[0] https://cgit.git.savannah.gnu.org/cgit/tar.git/commit/?id=75b03fdff48916bd0654677ed21379bdb0db016d
[1] https://cgit.git.savannah.gnu.org/cgit/attr.git/commit/?id=1cea2fc5e8b5c8a5f29abf1141399e01a57a3154
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