[PATCH] net: usb: cx82310_eth: bound partial receive continuation

[Pengpeng Hou <pengpeng@iscas.ac.cn>]

cx82310_rx_fixup() completes a packet that started in the previous URB
by copying dev->partial_rem bytes from the current skb. It then pulls
the same continuation extent, rounded up to an even byte count. The code
does not first prove that the current skb contains that continuation.

Add a fail-closed bound check before the copy and pull. If the
continuation is shorter than the pending packet state expects, drop that
pending partial packet before returning so later URBs are not consumed as
stale continuation bytes. This keeps the existing cross-URB packet
model, but avoids consuming bytes that are not present in the current
skb.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
diff --git a/drivers/net/usb/cx82310_eth.c b/drivers/net/usb/cx82310_eth.c
--- a/drivers/net/usb/cx82310_eth.c
+++ b/drivers/net/usb/cx82310_eth.c
@@ -242,7 +242,7 @@
  */
 static int cx82310_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 {
-	int len;
+	int len, pull_len;
 	struct sk_buff *skb2;
 	struct cx82310_priv *priv = dev->driver_priv;
 
@@ -251,6 +251,13 @@
 	 * end of that packet at the beginning.
 	 */
 	if (dev->partial_rem) {
+		pull_len = (dev->partial_rem + 1) & ~1;
+		if (skb->len < pull_len) {
+			dev->partial_len = 0;
+			dev->partial_rem = 0;
+			return 0;
+		}
+
 		len = dev->partial_len + dev->partial_rem;
 		skb2 = alloc_skb(len, GFP_ATOMIC);
 		if (!skb2)
@@ -261,7 +265,7 @@
 		memcpy(skb2->data + dev->partial_len, skb->data,
 		       dev->partial_rem);
 		usbnet_skb_return(dev, skb2);
-		skb_pull(skb, (dev->partial_rem + 1) & ~1);
+		skb_pull(skb, pull_len);
 		dev->partial_rem = 0;
 		if (skb->len < 2)
 			return 1;