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

> ---
> drivers/vhost/net.c | 7 ++++++-
> 1 files changed, 6 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index f0da2c3..29abd65 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -163,10 +163,15 @@ static void handle_tx(struct vhost_net *net)
> mutex_lock(&vq->mutex);
> vhost_disable_notify(&net->dev, vq);
>
> + zcopy = vhost_sock_zcopy(sock);
> + if (zcopy && !vq->ubufs) {
> + mutex_unlock(&vq->mutex);
> + return;
> + }
> +
> if (wmem < sock->sk->sk_sndbuf / 2)
> tx_poll_stop(net);
> hdr_size = vq->vhost_hlen;
> - zcopy = vhost_sock_zcopy(sock);
>
> for (;;) {
> /* Release DMAs done buffers first */


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