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SubjectRe: [PATCH 5/6] vhost_net: fix use after free of vq->ubufs
On 04/17/2012 06:22 PM, Michael S. Tsirkin wrote:
> On Tue, Apr 17, 2012 at 11:19:42AM +0800, Jason Wang wrote:
>> > On 04/16/2012 09:28 PM, Michael S. Tsirkin wrote:
>>> > >On Mon, Apr 16, 2012 at 02:08:25PM +0800, Jason Wang wrote:
>>>> > >>When zerocopy socket is used, ubufs pointer were used in handle_tx()
>>>> > >>without any validation. This would cause NULL pointer deference after
>>>> > >>it has been freed in vhost_net_set_backend(). Fix this by check the
>>>> > >>pointer before using it.
>>>> > >>
>>>> > >>Signed-off-by: Jason Wang<jasowang@redhat.com>
>>> > >
>>> > >OK so it's NULL dereference and not user after free:)
>>> > >Also could you clarify how does this happen pls?
>>> > >Don't we always initialize ubufs when vhost_sock_zcopy is set?
>> >
>> > The problem happens when we want to disable backend. At this time
>> > ubufs were assigned to NULL and it may be dereferenced by
>> > handle_tx():
> Heh, I see. How about
> - zcopy = vhost_sock_zcopy(sock);
> + zcopy = vq->ubufs;

Yes, It's more is simpler.


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