From: Al Viro <viro@zeniv.linux.org.uk>
To: Kees Cook <kees@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
brauner@kernel.org, jack@suse.cz, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
syzkaller-bugs@googlegroups.com,
syzbot <syzbot+1c486d0b62032c82a968@syzkaller.appspotmail.com>
Subject: Re: [syzbot] [fs?] [mm?] KCSAN: data-race in bprm_execve / copy_fs (4)
Date: Fri, 21 Mar 2025 01:44:23 +0000 [thread overview]
Message-ID: <20250321014423.GA2023217@ZenIV> (raw)
In-Reply-To: <202503201225.92C5F5FB1@keescook>
On Thu, Mar 20, 2025 at 01:09:38PM -0700, Kees Cook wrote:
> What I can imagine here is two failing execs racing a fork:
>
> A start execve
> B fork with CLONE_FS
> C start execve, reach check_unsafe_exec(), set fs->in_exec
> A bprm_execve() failure, clear fs->in_exec
> B copy_fs() increment fs->users.
> C bprm_execve() failure, clear fs->in_exec
>
> But I don't think this is a "real" flaw, though, since the locking is to
> protect a _successful_ execve from a fork (i.e. getting the user count
> right). A successful execve will de_thread, and I don't see any wrong
> counting of fs->users with regard to thread lifetime.
>
> Did I miss something in the analysis? Should we perform locking anyway,
> or add data race annotations, or something else?
Umm... What if C succeeds, ending up with suid sharing ->fs?
next prev parent reply other threads:[~2025-03-21 1:44 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-20 19:09 [syzbot] [fs?] [mm?] KCSAN: data-race in bprm_execve / copy_fs (4) syzbot
2025-03-20 20:09 ` Kees Cook
2025-03-21 1:44 ` Al Viro [this message]
2025-03-21 8:10 ` Kees Cook
2025-03-21 8:49 ` Christian Brauner
2025-03-21 8:45 ` Christian Brauner
2025-03-22 1:00 ` Al Viro
2025-03-22 6:26 ` Kees Cook
2025-03-22 10:15 ` Mateusz Guzik
2025-03-22 10:28 ` Christian Brauner
2025-03-22 10:23 ` Christian Brauner
2025-03-22 15:55 ` Oleg Nesterov
2025-03-22 18:50 ` Al Viro
2025-03-23 18:14 ` Oleg Nesterov
2025-03-23 20:57 ` Christian Brauner
2025-03-24 16:00 ` [PATCH] exec: fix the racy usage of fs_struct->in_exec Oleg Nesterov
2025-03-24 17:01 ` Mateusz Guzik
2025-03-24 18:27 ` Oleg Nesterov
2025-03-24 18:37 ` Oleg Nesterov
2025-03-24 22:24 ` Mateusz Guzik
2025-03-25 10:09 ` Oleg Nesterov
2025-03-25 11:01 ` Mateusz Guzik
2025-03-25 13:21 ` Oleg Nesterov
2025-03-25 13:30 ` Christian Brauner
2025-03-25 14:15 ` Mateusz Guzik
2025-03-25 14:46 ` Christian Brauner
2025-03-25 18:40 ` Kees Cook
2025-04-29 15:49 ` Oleg Nesterov
2025-04-29 16:57 ` Kees Cook
2025-04-29 17:12 ` Mateusz Guzik
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