linux-kernel - Re: [PATCH] Fix use-after-free of q->root_blkg and q->root

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Message-ID: <20121016232040.GH16166@google.com>
Date:	Tue, 16 Oct 2012 16:20:40 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Jun'ichi Nomura <j-nomura@...jp.nec.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix use-after-free of q->root_blkg and q->root_rl.blkg

Hello,

On Thu, Oct 11, 2012 at 10:31:46AM +0900, Jun'ichi Nomura wrote:
> >> -	if (ent == &q->root_blkg->q_node)
> >> +	if (q->root_blkg && ent == &q->root_blkg->q_node)
> > 
> > Can we fix it little differently. Little earlier in the code, we check for
> > if q->blkg_list is empty, then all the groups are gone, and there are
> > no more request lists hence and return NULL.
> > 
> > Current code:
> >         if (rl == &q->root_rl) {
> >                 ent = &q->blkg_list;
> > 
> > Modified code:
> >         if (rl == &q->root_rl) {
> >                 ent = &q->blkg_list;
> > 		/* There are no more block groups, hence no request lists */
> > 		if (list_empty(ent))
> > 			return NULL;
> > 	}

Do we need this at all?  q->root_blkg being NULL is completely fine
there and the comparison would work as expected, no?

Thanks.

-- 
tejun
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