On 2019/1/17 下午7:20, Toshiaki Makita wrote:
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.
Fixes: 186b3c998c50 ("virtio-net: support XDP_REDIRECT")
Signed-off-by: Toshiaki Makita <makita.toshiaki@xxxxxxxxxxxxx>
I wonder whether or not we could simply do:
if (prog) {
rcu_assign_pointer()
synchronize_net()
}
set queues
if (!prog) {
rcu_assign_pointer()
}
Thanks
---
drivers/net/virtio_net.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 204eedf..ae93f0e 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2424,14 +2424,16 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
}
}
- 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;
+ old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
+ if (!old_prog && prog) {
+ err = _virtnet_set_queues(vi, curr_qp + xdp_qp);
+ if (err)
+ goto err_new_prog;
+ 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)
@@ -2439,6 +2441,18 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
if (!prog)
virtnet_restore_guest_offloads(vi);
}
+ }
+
+ if (old_prog && !prog) {
+ synchronize_net();
+ err = _virtnet_set_queues(vi, curr_qp + xdp_qp);
+ if (err)
+ goto err_old_prog;
+ 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++) {
if (old_prog)
bpf_prog_put(old_prog);
if (netif_running(dev)) {
@@ -2450,7 +2464,11 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
return 0;
-err:
+err_old_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);
+err_new_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);
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