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Re: [Qemu-devel] [PATCH] qed: fix use-after-free during l2 cache commit

From: Amit Shah
Subject: Re: [Qemu-devel] [PATCH] qed: fix use-after-free during l2 cache commit
Date: Fri, 30 Sep 2011 16:57:59 +0530
User-agent: Mutt/1.5.21 (2010-09-15)

On (Fri) 30 Sep 2011 [11:39:11], Stefan Hajnoczi wrote:
> QED's metadata caching strategy allows two parallel requests to race for
> metadata lookup.  The first one to complete will populate the metadata
> cache and the second one will drop the data it just read in favor of the
> cached data.
> There is a use-after-free in qed_read_l2_table_cb() and
> qed_commit_l2_update() where l2_table->offset was used after the
> l2_table may have been freed due to a metadata lookup race.  Fix this by
> keeping the l2_offset in a local variable and not reaching into the
> possibly freed l2_table.
> Reported-by: Amit Shah <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> Hi Amit,
> Thanks for reporting the assertion failure you saw at http://fpaste.org/CDuv/.
> Does this patch fix the problem?

Yes, this fixes it.



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