On 2019/1/29 上午8:45, 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.
- 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@xxxxxxxxxxxxx>
---
drivers/net/virtio_net.c | 33 ++++++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 7 deletions(-)
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Thanks.
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