From: Al Viro <viro@zeniv.linux.org.uk>
To: Jann Horn <jannh@google.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
David Howells <dhowells@redhat.com>,
kernel list <linux-kernel@vger.kernel.org>
Subject: Re: BUG: d_path() races with do_move_mount() on ->mnt_ns, leading to use-after-free
Date: Tue, 13 Sep 2022 18:48:05 +0100 [thread overview]
Message-ID: <YyDCVSaA2Kjnz/a5@ZenIV> (raw)
In-Reply-To: <CAG48ez2dS04ONb-EVQGOtmeU6vTpKLe4J0W1yqa+Q9j+Hg3hFw@mail.gmail.com>
On Tue, Sep 13, 2022 at 07:14:56PM +0200, Jann Horn wrote:
> As the subject says, there's a race between d_path() (specifically
> __prepend_path()) looking at mnt->mnt_ns with is_anon_ns(), and
> do_move_mount() switching out the ->mnt_ns and freeing the old one.
> This can theoretically lead to a use-after-free read, but it doesn't
> seem to be very interesting from a security perspective, since all it
> gets you is a comparison of a value in freed memory with zero.
... with d_absolute_path() being the only caller that might even
theoretically care.
Anyway, shouldn't be hard to deal with - adding rcu_head to
struct mnt_namespace (anon-unioned with e.g. ->list) and turning kfree()
in free_mnt_ns() into kfree_rcu() ought to do it...
prev parent reply other threads:[~2022-09-13 18:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-13 17:14 BUG: d_path() races with do_move_mount() on ->mnt_ns, leading to use-after-free Jann Horn
2022-09-13 17:48 ` Al Viro [this message]
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