[PATCH net-next v2] net: qualcomm: rmnet: Fix use after free while sending command ack

[PATCH net-next v2] net: qualcomm: rmnet: Fix use after free while sending command ack

[Subash Abhinov Kasiviswanathan]

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.
Also, remove an unnecessary variable.

Fixes: ceed73a2cf4a ("drivers: net: ethernet: qualcomm: rmnet: Initial implementation")
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>

---
v1->v2: Rebase change on net-next instead as mentioned by David.
Also remove an unnecessary variable.
---
 drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
index 56a93df..3ee8ae9 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
@@ -67,7 +67,7 @@ static void rmnet_map_send_ack(struct sk_buff *skb,
 			       struct rmnet_port *port)
 {
 	struct rmnet_map_control_command *cmd;
-	int xmit_status;
+	struct net_device *dev = skb->dev;
 
 	if (port->data_format & RMNET_FLAGS_INGRESS_MAP_CKSUMV4)
 		skb_trim(skb,
@@ -78,9 +78,9 @@ 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);
+	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

Re: [PATCH net-next v2] net: qualcomm: rmnet: Fix use after free while sending command ack

[David Miller]

From: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Date: Mon,  4 Jun 2018 19:43:38 -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.
> Also, remove an unnecessary variable.
> 
> Fixes: ceed73a2cf4a ("drivers: net: ethernet: qualcomm: rmnet: Initial implementation")
> Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>

Applied.