lkml.org 
[lkml]   [2019]   [May]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH V2 2/4] vhost_net: fix possible infinite loop
Date
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>
---
The patch is needed for stable.
---
drivers/vhost/net.c | 29 +++++++++++++----------------
1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 061a06d..2d9df78 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);
--
1.8.3.1
\
 
 \ /
  Last update: 2019-05-17 06:30    [W:0.068 / U:5.384 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site