Subject: [PATCH net] net: qualcomm: rmnet: Fix use after free while sending command ack

From: Subash Abhinov Kasiviswanathan <[email-masked]>
Date: Sun, 3 Jun 2018 16:17:55 -0600

When sending an ack to a command packet, the skb is still referenced
after it is sent to the real device. Since the real device could
free the skb, the device pointer would be invalid.

Fixes: ceed73a2cf4a ("drivers: net: ethernet: qualcomm: rmnet: Initial implementation")
Signed-off-by: Subash Abhinov Kasiviswanathan <[email-masked]>
---
 drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
index 78fdad0..f530b07 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
@@ -67,6 +67,7 @@ static void rmnet_map_send_ack(struct sk_buff *skb,
 			       struct rmnet_port *port)
 {
 	struct rmnet_map_control_command *cmd;
+	struct net_device *dev = skb->dev;
 	int xmit_status;
 
 	if (port->data_format & RMNET_FLAGS_INGRESS_MAP_CKSUMV4) {
@@ -86,9 +87,9 @@ static void rmnet_map_send_ack(struct sk_buff *skb,
 	cmd = RMNET_MAP_GET_CMD_START(skb);
 	cmd->cmd_type = type & 0x03;
 
-	netif_tx_lock(skb->dev);
-	xmit_status = skb->dev->netdev_ops->ndo_start_xmit(skb, skb->dev);
-	netif_tx_unlock(skb->dev);
+	netif_tx_lock(dev);
+	xmit_status = dev->netdev_ops->ndo_start_xmit(skb, dev);
+	netif_tx_unlock(dev);
 }
 
 /* Process MAP command frame and send N/ACK message as appropriate. Message cmd
-- 
1.9.1