[PATCH] net: usbnet: Fix potential NULL pointer dereference

[Ren Mingshuai]

23ba07991dad said SKB can be NULL without describing the triggering
scenario. Always Check it before dereference to void potential NULL
pointer dereference.
Fix smatch warning:
drivers/net/usb/usbnet.c:1380 usbnet_start_xmit() error: we previously assumed 'skb' could be null (see line 1359)

Signed-off-by: Ren Mingshuai <renmingshuai@xxxxxxxxxx>
---
 drivers/net/usb/usbnet.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 64a9a80b2309..386cb1a4ff03 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1374,6 +1374,11 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
 		}
 	}
 
+	if (!skb) {
+		netif_dbg(dev, tx_err, dev->net, "tx skb is NULL\n");
+		goto drop;
+	}
+
 	if (!(urb = usb_alloc_urb (0, GFP_ATOMIC))) {
 		netif_dbg(dev, tx_err, dev->net, "no urb\n");
 		goto drop;
-- 
2.33.0