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

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Message-ID: <20120416060825.14140.32069.stgit@intel-e5620-16-2.englab.nay.redhat.com>
Date:	Mon, 16 Apr 2012 14:08:25 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	netdev@...r.kernel.org, xma@...ibm.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org, mst@...hat.com
Cc:	ebiederm@...ssion.com
Subject: [PATCH 5/6] vhost_net: fix use after free of vq->ubufs

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@...hat.com>
---
 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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