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

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Date: Tue, 27 Feb 2024 00:49:51 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Christian Brauner <brauner@...nel.org>, Arnd Bergmann <arnd@...db.de>
Cc: Icenowy Zheng <uwu@...nowy.me>, Huacai Chen <chenhuacai@...nel.org>, 
 WANG Xuerui <kernel@...0n.name>, 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, 2024-02-26 at 16:40 +0100, Christian Brauner wrote:

> > I definitely don't want to see a new time32 API added to
> > mips64 and the 32-bit architectures, so the existing stat64
> > interface won't work as a statx replacement.
> 
> I don't specifically care but the same way you don't want to see newer
> time32 apis added to architectures I don't want to have hacks in our
> system calls that aren't even a clear solution to the problem outlined
> in this thread.

So we should have a fstat_whatever64, IMO.

> Short of adding fstatx() the problem isn't solved by a new flag to
> statx() as explained in my other mails. But I'm probably missing
> something here because I find this notion of "design system calls for
> seccomp and the Chromium sandbox" to be an absurd notion and it makes me
> a bit impatient.

I'm sharing the feeling on seccomp and/or (mis)uses of it, but using
statx() or fstatat() for fstat() has a performance impact as they must
inspect path (do a uaccess) and make sure it's an empty string, and
Linus concluded "if the user want fstat, you should give the user fstat"
for this issue:

https://sourceware.org/pipermail/libc-alpha/2023-September/151365.html

If it was just seccomp I'd not comment on this topic at all.

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