wifi: mwifiex: Fix oob check condition in mwifiex_process_rx_packet

Only skip the code path trying to access the rfc1042 headers when the
buffer is too small, so the driver can still process packets without
rfc1042 headers.

Fixes: 1195852 ("wifi: mwifiex: Fix OOB and integer underflow when rx packets")
Signed-off-by: Pin-yen Lin <treapking@chromium.org>
Acked-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Matthew Wang <matthewmwang@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230908104308.1546501-1-treapking@chromium.org

drivers/net/wireless/marvell/mwifiex/sta_rx.c

@@ -86,7 +86,8 @@ int mwifiex_process_rx_packet(struct mwifiex_private *priv,
 	rx_pkt_len = le16_to_cpu(local_rx_pd->rx_pkt_length);
 	rx_pkt_hdr = (void *)local_rx_pd + rx_pkt_off;
 
-	if (sizeof(*rx_pkt_hdr) + rx_pkt_off > skb->len) {
+	if (sizeof(rx_pkt_hdr->eth803_hdr) + sizeof(rfc1042_header) +
+	    rx_pkt_off > skb->len) {
 		mwifiex_dbg(priv->adapter, ERROR,
 			    "wrong rx packet offset: len=%d, rx_pkt_off=%d\n",
 			    skb->len, rx_pkt_off);
@@ -95,12 +96,13 @@ int mwifiex_process_rx_packet(struct mwifiex_private *priv,
 		return -1;
 	}
 
-	if ((!memcmp(&rx_pkt_hdr->rfc1042_hdr, bridge_tunnel_header,
-		     sizeof(bridge_tunnel_header))) ||
-	    (!memcmp(&rx_pkt_hdr->rfc1042_hdr, rfc1042_header,
-		     sizeof(rfc1042_header)) &&
-	     ntohs(rx_pkt_hdr->rfc1042_hdr.snap_type) != ETH_P_AARP &&
-	     ntohs(rx_pkt_hdr->rfc1042_hdr.snap_type) != ETH_P_IPX)) {
+	if (sizeof(*rx_pkt_hdr) + rx_pkt_off <= skb->len &&
+	    ((!memcmp(&rx_pkt_hdr->rfc1042_hdr, bridge_tunnel_header,
+		      sizeof(bridge_tunnel_header))) ||
+	     (!memcmp(&rx_pkt_hdr->rfc1042_hdr, rfc1042_header,
+		      sizeof(rfc1042_header)) &&
+	      ntohs(rx_pkt_hdr->rfc1042_hdr.snap_type) != ETH_P_AARP &&
+	      ntohs(rx_pkt_hdr->rfc1042_hdr.snap_type) != ETH_P_IPX))) {
 		/*
 		 *  Replace the 803 header and rfc1042 header (llc/snap) with an
 		 *    EthernetII header, keep the src/dst and snap_type