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[PATCH] hv_netvsc: Make sure out channel is fully opened on send

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

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 <mgamal@xxxxxxxxxx>
 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(
+	ring_avail = hv_ringbuf_avail_percent(&out_channel->outbound);
 	if (ret == 0) {