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

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Message-ID: <20090211212142.GA3696@us.ibm.com>
Date:	Wed, 11 Feb 2009 15:21:42 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	David Howells <dhowells@...hat.com>
Cc:	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

Quoting David Howells (dhowells@...hat.com):
> 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.

Yikes, you're right.  I was thinking there was on hash table with
the key calculated from ns+uid, but instead each ns has its own
hash table keyed on uid.

> Anyway, I have no objection to your new patch.
> 
> Acked-by: David Howells <dhowells@...hat.com>

thanks,
-serge
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