linux-kernel - Re: namespaces?: bug at mm/slub.c:2750

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Message-ID: <6369.1234384961@redhat.com>
Date:	Wed, 11 Feb 2009 20:42:41 +0000
From:	David Howells <dhowells@...hat.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	dhowells@...hat.com, Vegard Nossum <vegard.nossum@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Sesterhenn <snakebyte@....de>, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: namespaces?: bug at mm/slub.c:2750

Serge E. Hallyn <serue@...ibm.com> wrote:

> Yes, but noone will pull the user_struct off the list without
> taking the lock.
> 
> what am I missing?

I believe that the hash link (uidhash_node) in the user_struct that is passed
to uid_hash_remove() points to, and is pointed to by the user_namespace to
which the user_struct belongs.

In which case calling put_user_ns() may kfree the head pointer of the list
_before_ hlist_del_init() is invoked - in which case hlist_del_init() will act
upon freed memory.

At least, I think it works like this.

Anyway, I have no objection to your new patch.

Acked-by: David Howells <dhowells@...hat.com>
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