net: usb: ax88179_178a: fix skb leak in ax88179_tx_fixup()

From: Yi Cong <[email protected]>

When the interface has NETIF_F_SG enabled and skb_linearize() fails in ax88179_tx_fixup(), the function returns NULL without freeing the skb.

usbnet_start_xmit() treats a NULL return from tx_fixup() as a drop (info->flags does not set FLAG_MULTI_PACKET for this driver), jumping to the "drop" label where it does if (skb) dev_kfree_skb_any(skb). Because tx_fixup() returned NULL, the local skb variable in usbnet_start_xmit() is NULL, so the original skb is never freed — a memory leak on every TX frame whose linearization fails (i.e. under memory pressure).

Free the skb before returning, matching the error handling already used for the pskb_expand_head() failure path in the same function.

---
 drivers/net/usb/ax88179_178a.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index 98f899ea2e94..81d8412ce8e2 100644
@@ -1487,8 +1487,10 @@ ax88179_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
 
 	headroom = skb_headroom(skb) - 8;
 
-	if ((dev->net->features & NETIF_F_SG) && skb_linearize(skb))
+	if ((dev->net->features & NETIF_F_SG) && skb_linearize(skb)) {
+		dev_kfree_skb_any(skb);
 		return NULL;
+	}
 
 	if ((skb_header_cloned(skb) || headroom < 0) &&
 	    pskb_expand_head(skb, headroom < 0 ? 8 : 0, 0, GFP_ATOMIC)) {

2.25.1