From: Christoph Hellwig <hch@infradead.org>
To: Dmitry Kadashev <dkadashev@gmail.com>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Jens Axboe <axboe@kernel.dk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] namei: Fix use after free in kern_path_locked
Date: Wed, 1 Sep 2021 10:12:00 +0100 [thread overview]
Message-ID: <YS9D4AlEsaCxLFV0@infradead.org> (raw)
In-Reply-To: <CAOKbgA49wFL3+-QAQ+DEnNVzCjYcN0qmnVHGo1x=eXeyzNxvsw@mail.gmail.com>
On Wed, Sep 01, 2021 at 02:35:08PM +0700, Dmitry Kadashev wrote:
> On Wed, Sep 1, 2021 at 7:13 AM Stephen Brennan
> <stephen.s.brennan@oracle.com> wrote:
> >
> > In 0ee50b47532a ("namei: change filename_parentat() calling
> > conventions"), filename_parentat() was made to always put the struct
> > filename before returning, and kern_path_locked() was migrated to this
> > calling convention. However, kern_path_locked() uses the "last"
> > parameter to lookup and potentially create a new dentry. The last
> > parameter contains the last component of the path and points within the
> > filename, which was recently freed at the end of filename_parentat().
> > Thus, when kern_path_locked() calls __lookup_hash(), it is using the
> > filename after it has already been freed.
> >
> > To avoid this, switch back to __filename_parentat() and place a putname
> > at the end of the function, once all uses are completed.
>
> Ouch. Thanks for taking care of this, Stephen. I guess
> filename_parentat() should be killed, since kern_path_locked() was the
> only place it's used in and it always results in danging "last",
> provoking bugs just like this one. I can send a patch on top of this if
> you prefer.
Yes. And then rename __filename_parentat to filename_parentat, please.
next prev parent reply other threads:[~2021-09-01 9:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-01 0:13 [PATCH] namei: Fix use after free in kern_path_locked Stephen Brennan
2021-09-01 7:35 ` Dmitry Kadashev
2021-09-01 9:12 ` Christoph Hellwig [this message]
2021-09-01 14:47 ` Dmitry Kadashev
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