linux-kernel - Re: fs: NULL deref in atime_needs

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Date:	Mon, 22 Feb 2016 17:23:14 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Mickaël Salaün <mic@...ikod.net>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: fs: NULL deref in atime_needs_update

On Mon, Feb 22, 2016 at 12:20:30PM +0100, Dmitry Vyukov wrote:

> I've reproduced the second report (the one originating in openat) with
> this patch and the WARNING did _not_ fire:

Lovely...  Could you dump your inode.o on anonftp somewhere?  Or post
the disassembled atime_needs_update, for that matter - shouldn't be
all that long...  .config (and gcc version) you are using would also be nice.

On the face of it, NULL inode is a plausible source of that one, but
it's _very_ odd.  It would have to be NULL ->link_inode, and since the
warning hadn't triggered, there was a successful should_follow_link(),
with NULL inode argument.

	Could you slap WARN_ON(!inode) in pick_link()?  Or even
WARN_ON(IS_ERR_OR_NULL(inode)), for that matter...