Re: [PATCH] LoongArch: Define __ARCH_WANT_NEW_STAT in unistd.h

[Xi Ruoyao <xry111@xry111.site>]

On Sat, 2024-06-15 at 13:47 +0200, Arnd Bergmann wrote:

/* snip */

> > > > We can only wait for the seccomp side to be fixed now? Or we can get
> > > > this patch upstream for LoongArch64 at the moment, and wait for
> > > > seccomp to fix RISCV32 (and LoongArch32) in future?
> > > 
> > > I'm wondering why not just introduce a new syscall or extend statx with
> > > a new flag, as we've discussed many times.  They have their own
> > > disadvantages but better than this, IMO.
> > We should move things forward, in any way. :)
> 
> Wouldn't it be sufficient to move the AT_EMPTY_PATH hack
> from vfs_fstatat() to vfs_statx() so we can make them
> behave the same way?
> 
> As far as I can tell, the only difference between the two is
> that fstatat64() and similar already has added the check for
> zero-length strings in order to make using vfs_fstatat()
> fast and safe when called from glibc stat().

Do you mean https://git.kernel.org/torvalds/c/9013c51c630a?  It (only
partially) fix the performance issue but it won't help seccomp.  The
problem is you cannot check if the string is zero-length with seccomp.
Thus seccomp cannot audit fstatat properly as well.

In [Firefox] *all* fstatat (and statx) calls are trapped and *the signal
handler* audit this fstatat call.  If flags & AT_EMPTY_PATH and path is
zero-length, it calls fstat to do the job.  But on LoongArch there is no
way to "do the job" as the only stat-family call is statx.

[Firefox]:https://searchfox.org/mozilla-central/source/security/sandbox/linux/SandboxFilter.cpp#364

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University