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

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Message-ID: <f59d73fb-7d3e-4c55-821a-082032267978@xen0n.name>
Date: Wed, 21 Feb 2024 18:49:17 +0800
From: WANG Xuerui <kernel@...0n.name>
To: Xi Ruoyao <xry111@...111.site>, linux-api@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.de>, Christian Brauner <brauner@...nel.org>,
 Kees Cook <keescook@...omium.org>, Huacai Chen <chenhuacai@...nel.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>, Icenowy Zheng <uwu@...nowy.me>,
 "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 2/21/24 18:31, Xi Ruoyao wrote:
> On Wed, 2024-02-21 at 14:31 +0800, Xi Ruoyao wrote:
>> On Wed, 2024-02-21 at 14:09 +0800, WANG Xuerui wrote:
>>
>>> - just restore fstat and be done with it;
>>> - add a flag to statx so we can do the equivalent of just fstat(fd,
>>> &out) with statx, and ensuring an error happens if path is not empty in
>>> that case;
>> It's worse than "just restore fstat" considering the performance.  Read
>> this thread:
>> https://sourceware.org/pipermail/libc-alpha/2023-September/151320.html
> Hmm, but it looks like statx already suffers the same performance issue.
> And in this libc-alpha discussion Linus said:
>
>     If the user asked for 'fstat()', just give the user 'fstat()'.
>     
> So to me we should just add fstat (and use it in Glibc for LoongArch, only
> falling back to statx if fstat returns -ENOSYS), or am I missing something?

Or we could add a AT_STATX_NULL_PATH flag and mandate that `path` must 
be NULL if this flag is present -- then with simple checks we could have 
statx(fd, NULL, AT_STATX_NULL_PATH, STATX_BASIC_STATS, &out) that's both 
fstat-like and fast.

-- 
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/