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

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Date: Tue, 02 Jul 2024 19:06:53 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Huacai Chen" <chenhuacai@...nel.org>
Cc: "Xi Ruoyao" <xry111@...111.site>, "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 Tue, Jul 2, 2024, at 17:36, Huacai Chen wrote:
> On Mon, Jul 1, 2024 at 7:59 PM Arnd Bergmann <arnd@...db.de> wrote:
>> 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.
> Would you mind if I restore newstat for LoongArch64 even if this patch exist?

I still prefer not add newstat back: it's easier to
get applications to correctly implement the statx() code
path if there are more architectures that only have that.

       Arnd