4.20-stable review patch. If anyone has any objections, please let me know.
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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);