linux-kernel - Re: [PATCH] LoongArch: Define __ARCH_WANT_NEW

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Date: Sat, 15 Jun 2024 21:12:26 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Arnd Bergmann <arnd@...db.de>, Huacai Chen <chenhuacai@...nel.org>
Cc: Huacai Chen <chenhuacai@...ngson.cn>, loongarch@...ts.linux.dev,
 Linux-Arch <linux-arch@...r.kernel.org>, Xuefeng Li
 <lixuefeng@...ngson.cn>, guoren <guoren@...nel.org>, WANG Xuerui
 <kernel@...0n.name>, Jiaxun Yang <jiaxun.yang@...goat.com>,
 linux-kernel@...r.kernel.org,  loongson-kernel@...ts.loongnix.cn,
 stable@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Define __ARCH_WANT_NEW_STAT in unistd.h

On Sat, 2024-06-15 at 20:12 +0800, Xi Ruoyao wrote:
> 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

Just spent some brain cycles to make a quick hack adding a new statx
flag.  Patch attached.

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University

View attachment "0001-RFC-vfs-Add-AT_FORCE_EMPTY_PATH.patch" of type "text/x-patch" (3908 bytes)