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From:   Mohammed Gamal <mgamal@redhat.com>
To:     netdev@vger.kernel.org, sthemmin@microsoft.com
Cc:     devel@linuxdriverproject.org, davem@davemloft.net,
        vkuznets@redhat.com, otubo@redhat.com,
        linux-kernel@vger.kernel.org, Mohammed Gamal <mgamal@redhat.com>
Subject: [PATCH] hv_netvsc: Make sure out channel is fully opened on send
Date:   Tue, 13 Mar 2018 20:06:50 +0100
Message-Id: <1520968010-20733-1-git-send-email-mgamal@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 <mgamal@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);
 
-- 
1.8.3.1