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    SubjectRe: [PATCH 5/6] vhost_net: fix use after free of vq->ubufs
    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;

    --
    MST


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