linux-kernel - Re: [PATCH 2/2] vfs: support statx(..., NULL, AT_EMPTY

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Message-Id: <1b5d0840-766b-4c3b-8579-3c2c892c4d74@app.fastmail.com>
Date: Mon, 01 Jul 2024 13:59:12 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Xi Ruoyao" <xry111@...111.site>, "Huacai Chen" <chenhuacai@...nel.org>
Cc: "Mateusz Guzik" <mjguzik@...il.com>,
 "Christian Brauner" <brauner@...nel.org>,
 "Alexander Viro" <viro@...iv.linux.org.uk>, "Jan Kara" <jack@...e.cz>,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 io-uring@...r.kernel.org, "Jens Axboe" <axboe@...nel.dk>,
 "Linus Torvalds" <torvalds@...ux-foundation.org>, loongarch@...ts.linux.dev
Subject: Re: [PATCH 2/2] vfs: support statx(..., NULL, AT_EMPTY_PATH, ...)

On Sun, Jun 30, 2024, at 04:39, Xi Ruoyao wrote:
> On Sun, 2024-06-30 at 09:40 +0800, Huacai Chen wrote:
>> > 
>> > Yes, both Linus and Christian hates introducing a new AT_ flag for
>> > this.
>> > 
>> > This patch just makes statx(fd, NULL, AT_EMPTY_PATH, ...) behave
>> > like
>> > statx(fd, "", AT_EMPTY_PATH, ...) instead.  NULL avoids the
>> > performance
>> > issue and it's also audit-able by seccomp BPF.
>> To be honest, I still want to restore __ARCH_WANT_NEW_STAT. Because
>> even if statx() becomes audit-able, it is still blacklisted now.
>
> Then patch the sandbox to allow it.
>
> The sandbox **must** be patched anyway or it'll be broken on all 32-bit
> systems after 2037.  [Unless they'll unsupport all 32-bit systems before
> 2037.]

More importantly, the sandbox won't be able to support any 32-bit
targets that support running after 2037, regardless of how long
the sandbox supports them: if you turn off COMPAT_32BIT_TIME today
in order to be sure those don't get called by accident, the
fallback is immediately broken.

      Arnd