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Message-ID: <92aac2c0-0d32-5920-d191-47bd0f5f0290@gmail.com> Date: Mon, 19 Jun 2023 23:49:44 +0200 From: Gabriel Ravier <gabravier@...il.com> To: musl@...ts.openwall.com, Mike Gilbert <floppym@...too.org> Subject: Re: faccessat behavior on old kernels (<5.8) On 6/19/23 20:14, Mike Gilbert wrote: > I am not subscribed, so please CC me on replies. > > I received a bug report on Gentoo Linux. > > https://bugs.gentoo.org/908765 > > There appears to be a difference in behavior between musl and glibc > when running on Linux kernels that lack support for the faccessat2 > system call. > > On glibc, the following call returns 0. On musl, it returns -1 and > sets errno to EINVAL. > > faccessat(AT_FDCWD, "/dev/null", F_OK, AT_SYMLINK_NOFOLLOW); > > On older kernels, the underlying faccessat2 syscall returns -1 / ENOSYS. > glibc follows that up with an fstatat64 with equivalent arguments. > musl immediately fails with -1 / EINVAL. > > Relevant code: > > https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/faccessat.c;h=0ccbd778b5f4d61f9121b6aeb59782c21ae647a0;hb=a704fd9a133bfb10510e18702f48a6a9c88dbbd5#l36 > > https://git.musl-libc.org/cgit/musl/tree/src/unistd/faccessat.c?h=v1.2.4#n34 To be more precise, the difference is that musl refuses to use its fallback when `AT_SYMLINK_NOFOLLOW` is set, whereas glibc does so - I don't know if musl's workaround would work in this case, though, given how different it is from anything glibc does.
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