linux-kernel - Re: Chromium sandbox on LoongArch and statx -- seccomp deep argument inspection again?

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Date: Mon, 26 Feb 2024 13:57:55 +0100
From: Christian Brauner <brauner@...nel.org>
To: Xi Ruoyao <xry111@...111.site>
Cc: Arnd Bergmann <arnd@...db.de>, Icenowy Zheng <uwu@...nowy.me>, 
	Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, 
	Adhemerval Zanella <adhemerval.zanella@...aro.org>, Rich Felker <dalias@...ifal.cx>, linux-api@...r.kernel.org, 
	Kees Cook <keescook@...omium.org>, Xuefeng Li <lixuefeng@...ngson.cn>, 
	Jianmin Lv <lvjianmin@...ngson.cn>, Xiaotian Wu <wuxiaotian@...ngson.cn>, 
	WANG Rui <wangrui@...ngson.cn>, Miao Wang <shankerwangmiao@...il.com>, 
	"loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>, Linux-Arch <linux-arch@...r.kernel.org>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Chromium sandbox on LoongArch and statx -- seccomp deep argument
 inspection again?

On Mon, Feb 26, 2024 at 07:57:56PM +0800, Xi Ruoyao wrote:
> On Mon, 2024-02-26 at 10:20 +0100, Arnd Bergmann wrote:
> 
> /* snip */
> 
> > 
> > > Or maybe we can just introduce a new AT_something to make statx
> > > completely ignore pathname but behave like AT_EMPTY_PATH + "".

I'm not at all convinced about doing custom semantics for this.

> > I think this is better than going back to fstat64_time64(), but
> > it's still not great because
> > 
> > - all the reserved flags on statx() are by definition incompatible
> >   with existing kernels that return -EINVAL for any flag they do
> >   not recognize.
> 
> Oops, we are deeming passing undefined flags in "mask" undefined
> behavior but not "flags", thus "wild software" may be relying on EINVAL
> for invalid flags...  We *might* make this new AT_xxx a bit in mask
> instead of flags but it would be very dirty IMO.

Uhm, no. AT_* flags have nothing to do in statx()'s mask argument at all.