[2/4] vhost_net: fix possible infinite loop
diff mbox series

Message ID 1565239415-11087-3-git-send-email-tyhicks@canonical.com
State New
Headers show
Series
  • CVE-2019-3900: vhost DoS
Related show

Commit Message

Tyler Hicks Aug. 8, 2019, 4:43 a.m. UTC
From: Jason Wang <jasowang@redhat.com>

When the rx buffer is too small for a packet, we will discard the vq
descriptor and retry it for the next packet:

while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk,
					      &busyloop_intr))) {
...
	/* On overrun, truncate and discard */
	if (unlikely(headcount > UIO_MAXIOV)) {
		iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
		err = sock->ops->recvmsg(sock, &msg,
					 1, MSG_DONTWAIT | MSG_TRUNC);
		pr_debug("Discarded rx packet: len %zd\n", sock_len);
		continue;
	}
...
}

This makes it possible to trigger a infinite while..continue loop
through the co-opreation of two VMs like:

1) Malicious VM1 allocate 1 byte rx buffer and try to slow down the
   vhost process as much as possible e.g using indirect descriptors or
   other.
2) Malicious VM2 generate packets to VM1 as fast as possible

Fixing this by checking against weight at the end of RX and TX
loop. This also eliminate other similar cases when:

- userspace is consuming the packets in the meanwhile
- theoretical TOCTOU attack if guest moving avail index back and forth
  to hit the continue after vhost find guest just add new buffers

This addresses CVE-2019-3900.

Fixes: d8316f3991d20 ("vhost: fix total length when packets are too short")
Fixes: 3a4d5c94e9593 ("vhost_net: a kernel-level virtio server")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

CVE-2019-3900

(cherry picked from commit e2412c07f8f3040593dfb88207865a3cd58680c0)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
---
 drivers/vhost/net.c | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

Patch
diff mbox series

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 061a06dc12a3..2d9df786a9d3 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -773,7 +773,7 @@  static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
 	int sent_pkts = 0;
 	bool sock_can_batch = (sock->sk->sk_sndbuf == INT_MAX);
 
-	for (;;) {
+	do {
 		bool busyloop_intr = false;
 
 		if (nvq->done_idx == VHOST_NET_BATCH)
@@ -839,9 +839,7 @@  static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
 		vq->heads[nvq->done_idx].id = cpu_to_vhost32(vq, head);
 		vq->heads[nvq->done_idx].len = 0;
 		++nvq->done_idx;
-		if (vhost_exceeds_weight(vq, ++sent_pkts, total_len))
-			break;
-	}
+	} while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len)));
 
 	vhost_tx_batch(net, nvq, sock, &msg);
 }
@@ -866,7 +864,7 @@  static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
 	bool zcopy_used;
 	int sent_pkts = 0;
 
-	for (;;) {
+	do {
 		bool busyloop_intr;
 
 		/* Release DMAs done buffers first */
@@ -943,10 +941,7 @@  static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
 		else
 			vhost_zerocopy_signal_used(net, vq);
 		vhost_net_tx_packet(net);
-		if (unlikely(vhost_exceeds_weight(vq, ++sent_pkts,
-						  total_len)))
-			break;
-	}
+	} while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len)));
 }
 
 /* Expects to be always run from workqueue - which acts as
@@ -1144,8 +1139,11 @@  static void handle_rx(struct vhost_net *net)
 		vq->log : NULL;
 	mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF);
 
-	while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk,
-						      &busyloop_intr))) {
+	do {
+		sock_len = vhost_net_rx_peek_head_len(net, sock->sk,
+						      &busyloop_intr);
+		if (!sock_len)
+			break;
 		sock_len += sock_hlen;
 		vhost_len = sock_len + vhost_hlen;
 		headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx,
@@ -1230,12 +1228,11 @@  static void handle_rx(struct vhost_net *net)
 			vhost_log_write(vq, vq_log, log, vhost_len,
 					vq->iov, in);
 		total_len += vhost_len;
-		if (unlikely(vhost_exceeds_weight(vq, ++recv_pkts, total_len)))
-			goto out;
-	}
+	} while (likely(!vhost_exceeds_weight(vq, ++recv_pkts, total_len)));
+
 	if (unlikely(busyloop_intr))
 		vhost_poll_queue(&vq->poll);
-	else
+	else if (!sock_len)
 		vhost_net_enable_vq(net, vq);
 out:
 	vhost_net_signal_used(nvq);
@@ -1328,7 +1325,7 @@  static int vhost_net_open(struct inode *inode, struct file *f)
 	}
 	vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX,
 		       UIO_MAXIOV + VHOST_NET_BATCH,
-		       VHOST_NET_WEIGHT, VHOST_NET_PKT_WEIGHT);
+		       VHOST_NET_PKT_WEIGHT, VHOST_NET_WEIGHT);
 
 	vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, EPOLLOUT, dev);
 	vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, EPOLLIN, dev);