On Tue, 13 Mar 2018 20:06:50 +0100
Mohammed Gamal <mga...@redhat.com> wrote:
> Dring high network traffic changes to network interface parameters
> such as number of channels or MTU can cause a kernel panic with a NULL
> pointer dereference. This is due to netvsc_device_remove() being
> called and deallocating the channel ring buffers, which can then be
> accessed by netvsc_send_pkt() before they're allocated on calling
> netvsc_device_add()
>
> The patch fixes this problem by checking the channel state and returning
> ENODEV if not yet opened. We also move the call to hv_ringbuf_avail_percent()
> which may access the uninitialized ring buffer.
>
> Signed-off-by: Mohammed Gamal <mga...@redhat.com>
> ---
> drivers/net/hyperv/netvsc.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
> index 0265d70..44a8358 100644
> --- a/drivers/net/hyperv/netvsc.c
> +++ b/drivers/net/hyperv/netvsc.c
> @@ -757,7 +757,7 @@ static inline int netvsc_send_pkt(
> struct netdev_queue *txq = netdev_get_tx_queue(ndev, packet->q_idx);
> u64 req_id;
> int ret;
> - u32 ring_avail = hv_ringbuf_avail_percent(&out_channel->outbound);
> + u32 ring_avail;
>
> nvmsg.hdr.msg_type = NVSP_MSG1_TYPE_SEND_RNDIS_PKT;
> if (skb)
> @@ -773,7 +773,7 @@ static inline int netvsc_send_pkt(
>
> req_id = (ulong)skb;
>
> - if (out_channel->rescind)
> + if (out_channel->rescind || out_channel->state != CHANNEL_OPENED_STATE)
> return -ENODEV;
>
> if (packet->page_buf_cnt) {
> @@ -791,6 +791,7 @@ static inline int netvsc_send_pkt(
>
> VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> }
>
> + ring_avail = hv_ringbuf_avail_percent(&out_channel->outbound);
> if (ret == 0) {
> atomic_inc_return(&nvchan->queue_sends);
>
Thanks for your patch. Yes there are races with the current update
logic. The root cause goes higher up in the flow; the send queues should
be stopped before netvsc_device_remove is called. Solving it where you tried
to is racy and not going to work reliably.
Network patches should go to net...@vger.kernel.org
You can't move the ring_avail check until after the vmbus_sendpacket because
that will break the flow control logic.
Instead, you should just move the avail_read check until just after the
existing rescind
check.
Also, you shouldn't need to check for OPENED_STATE, just rescind is enough.
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