[PATCH 4.20 31/80] virtio_net: Dont process redirected XDP frames when XDP is disabled

Greg Kroah-Hartman
2019-02-04T10:52:37Z

From: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>

[ Upstream commit 03aa6d34868c07b2b1b8b2db080602d7ec528173 ]

Commit 8dcc5b0ab0ec ("virtio_net: fix ndo_xdp_xmit crash towards dev not
ready for XDP") tried to avoid access to unexpected sq while XDP is
disabled, but was not complete.

There was a small window which causes out of bounds sq access in
virtnet_xdp_xmit() while disabling XDP.

An example case of
- curr_queue_pairs = 6 (2 for SKB and 4 for XDP)
- online_cpu_num = xdp_queue_paris = 4
when XDP is enabled:

CPU 0 CPU 1
(Disabling XDP) (Processing redirected XDP frames)

virtnet_xdp_xmit()
virtnet_xdp_set()
_virtnet_set_queues()
set curr_queue_pairs (2)
check if rq->xdp_prog is not NULL
virtnet_xdp_sq(vi)
qp = curr_queue_pairs -
xdp_queue_pairs +
smp_processor_id()
= 2 - 4 + 1 = -1
sq = &vi->sq[qp] // out of bounds access
set xdp_queue_pairs (0)
rq->xdp_prog = NULL

Basically we should not change curr_queue_pairs and xdp_queue_pairs
while someone can read the values. Thus, when disabling XDP, assign NULL
to rq->xdp_prog first, and wait for RCU grace period, then change
xxx_queue_pairs.
Note that we need to keep the current order when enabling XDP though.

- v2: Make rcu_assign_pointer/synchronize_net conditional instead of
_virtnet_set_queues.

Fixes: 186b3c998c50 ("virtio-net: support XDP_REDIRECT")
Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/virtio_net.c | 33 ++++++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 7 deletions(-)

--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2409,6 +2409,10 @@ static int virtnet_xdp_set(struct net_de
return -ENOMEM;
}

+ old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
+ if (!prog && !old_prog)
+ return 0;
+
if (prog) {
prog = bpf_prog_add(prog, vi->max_queue_pairs - 1);
if (IS_ERR(prog))
@@ -2423,21 +2427,30 @@ static int virtnet_xdp_set(struct net_de
}
}

+ if (!prog) {
+ for (i = 0; i < vi->max_queue_pairs; i++) {
+ rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
+ if (i == 0)
+ virtnet_restore_guest_offloads(vi);
+ }
+ synchronize_net();
+ }
+
err = _virtnet_set_queues(vi, curr_qp + xdp_qp);
if (err)
goto err;
netif_set_real_num_rx_queues(dev, curr_qp + xdp_qp);
vi->xdp_queue_pairs = xdp_qp;

- for (i = 0; i < vi->max_queue_pairs; i++) {
- old_prog = rtnl_dereference(vi->rq[i].xdp_prog);
- rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
- if (i == 0) {
- if (!old_prog)
+ if (prog) {
+ for (i = 0; i < vi->max_queue_pairs; i++) {
+ rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
+ if (i == 0 && !old_prog)
virtnet_clear_guest_offloads(vi);
- if (!prog)
- virtnet_restore_guest_offloads(vi);
}
+ }
+
+ for (i = 0; i < vi->max_queue_pairs; i++) {
if (old_prog)
bpf_prog_put(old_prog);
if (netif_running(dev)) {
@@ -2450,6 +2463,12 @@ static int virtnet_xdp_set(struct net_de
return 0;

err:
+ if (!prog) {
+ virtnet_clear_guest_offloads(vi);
+ for (i = 0; i < vi->max_queue_pairs; i++)
+ rcu_assign_pointer(vi->rq[i].xdp_prog, old_prog);
+ }
+
if (netif_running(dev)) {
for (i = 0; i < vi->max_queue_pairs; i++) {
virtnet_napi_enable(vi->rq[i].vq, &vi->rq[i].napi);