net: dsa: sja1105: Check return value

Return NULL if we got unexpected value from skb_trim_rcsum() in
sja1110_rcv_inband_control_extension()

Fixes: 4913b8e ("net: dsa: add support for the SJA1110 native tagging protocol")
Signed-off-by: Artem Chernyshev <artem.chernyshev@red-soft.ru>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20221201140032.26746-3-artem.chernyshev@red-soft.ru
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/tag_sja1105.c

@@ -665,7 +665,8 @@ static struct sk_buff *sja1110_rcv_inband_control_extension(struct sk_buff *skb,
 		 * padding and trailer we need to account for the fact that
 		 * skb->data points to skb_mac_header(skb) + ETH_HLEN.
 		 */
-		pskb_trim_rcsum(skb, start_of_padding - ETH_HLEN);
+		if (pskb_trim_rcsum(skb, start_of_padding - ETH_HLEN))
+			return NULL;
 	/* Trap-to-host frame, no timestamp trailer */
 	} else {
 		*source_port = SJA1110_RX_HEADER_SRC_PORT(rx_header);