linux-kernel - Re: [PATCH] Fix the race between the fget() and close()

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Message-ID: <20130827004852.GH27005@ZenIV.linux.org.uk>
Date:	Tue, 27 Aug 2013 01:48:52 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix the race between the fget() and close()

On Tue, Aug 27, 2013 at 01:42:47AM +0100, Al Viro wrote:
> Might be buggered refcounting on struct file somewhere (i.e. extra fput() done,
> getting the file freed *before* close(), leaving a dangling pointer in
> descriptor table).  Might be memory corruption of some kind, slapping junk
> pointer into descriptor table.  Might be buggered refcounting on struct
> dentry - if extra dput() is done somewhere, dentry might get freed under
> us or become negative.
> 
> Hell, might be buggered refcounting on descriptor table - binder is playing
> interesting games there.  Try to reproduce that with CONFIG_DEBUG_KMEMLEAK
> and slab debugging turned on, see if you hit anything from those; if it's
> more or less readily reproducible, I would start with that - too many
> scenarios involve broken refcounting of one sort or another.

Nevermind dentry refcounting - you get NULL dentry, not NULL inode.
Other scenarios still remain, so I'd really recommend slab/kmemleak
debugging turned on.
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