net: usb: smsc75xx: Move packet length check to prevent kernel panic in skb_pull

Packet length check needs to be located after size and align_count
calculation to prevent kernel panic in skb_pull() in case
rx_cmd_a & RX_CMD_A_RED evaluates to true.

Fixes: d8b22831 ("net: usb: smsc75xx: Limit packet length to skb->len")
Signed-off-by: Szymon Heidrich <szymon.heidrich@gmail.com>
Link: https://lore.kernel.org/r/20230316110540.77531-1-szymon.heidrich@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/usb/smsc75xx.c

@@ -2200,6 +2200,13 @@ static int smsc75xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 		size = (rx_cmd_a & RX_CMD_A_LEN) - RXW_PADDING;
 		align_count = (4 - ((size + RXW_PADDING) % 4)) % 4;
 
+		if (unlikely(size > skb->len)) {
+			netif_dbg(dev, rx_err, dev->net,
+				  "size err rx_cmd_a=0x%08x\n",
+				  rx_cmd_a);
+			return 0;
+		}
+
 		if (unlikely(rx_cmd_a & RX_CMD_A_RED)) {
 			netif_dbg(dev, rx_err, dev->net,
 				  "Error rx_cmd_a=0x%08x\n", rx_cmd_a);
@@ -2212,8 +2219,7 @@ static int smsc75xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 				dev->net->stats.rx_frame_errors++;
 		} else {
 			/* MAX_SINGLE_PACKET_SIZE + 4(CRC) + 2(COE) + 4(Vlan) */
-			if (unlikely(size > (MAX_SINGLE_PACKET_SIZE + ETH_HLEN + 12) ||
-				     size > skb->len)) {
+			if (unlikely(size > (MAX_SINGLE_PACKET_SIZE + ETH_HLEN + 12))) {
 				netif_dbg(dev, rx_err, dev->net,
 					  "size err rx_cmd_a=0x%08x\n",
 					  rx_cmd_a);