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From: Christian Brauner <brauner@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Kees Cook" <kees@kernel.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Zbigniew Jędrzejewski-Szmek" <zbyszek@in.waw.pl>,
	"Tycho Andersen" <tandersen@netflix.com>,
	"Aleksa Sarai" <cyphar@cyphar.com>,
	"Eric Biederman" <ebiederm@xmission.com>,
	"Jan Kara" <jack@suse.cz>,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case
Date: Sun, 1 Dec 2024 19:37:22 +0100	[thread overview]
Message-ID: <20241201-seerosen-opern-8dfda1f79c50@brauner> (raw)
In-Reply-To: <CAHk-=wgcbq=2N8m5X8vJuUNgM9gpVjqpQzrnCsu19MP8SV5TYA@mail.gmail.com>

On Sun, Dec 01, 2024 at 08:54:41AM -0800, Linus Torvalds wrote:
> On Sun, 1 Dec 2024 at 06:17, Christian Brauner <brauner@kernel.org> wrote:
> >
> > /*
> >  * Hold rcu lock to keep the name from being freed behind our back.
> >  * Use cquire semantics to make sure the terminating NUL from
> >  * __d_alloc() is seen.
> >  *
> >  * Note, we're deliberately sloppy here. We don't need to care about
> >  * detecting a concurrent rename and just want a sensible name.
> >  */
> 
> Sure. Note that even "sensible" isn't truly guaranteed in theory,
> since a concurrent rename could be doing a "memcpy()" into the
> dentry->d_name.name area at the same time on another CPU.

Yeah, I saw, if the dname.name assignment is reorded to happen before
the memcpy() afaict. Anyway, it's not that important especially since
PR_SET_MM_MAP puts comm, auxv etc. fully under user control anyway.


  reply	other threads:[~2024-12-01 18:37 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-11-30  4:54 Kees Cook
2024-11-30  5:55 ` Aleksa Sarai
2024-12-04 23:50   ` Zbigniew Jędrzejewski-Szmek
2024-11-30 12:29 ` Christian Brauner
2024-11-30 18:02   ` Linus Torvalds
2024-12-01 14:17     ` Christian Brauner
2024-12-01 16:54       ` Linus Torvalds
2024-12-01 18:37         ` Christian Brauner [this message]
2024-11-30 20:28 ` Mateusz Guzik
2024-11-30 21:34   ` Linus Torvalds

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