scsi: libfc: Prevent integer overflow in fc_fcp_recv_data()

The "offset" comes from the skb->data that we received.  Here the code
is verifying that "offset + len" is within bounds however it does not
take integer overflows into account.  Use size_add() to be safe.

This would only be an issue on 32bit systems which are probably a very
small percent of the users.  Still, it's worth fixing just for
correctness sake.

Fixes: 42e9a92 ("[SCSI] libfc: A modular Fibre Channel library")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Message-Id: <aNvPMet7TPtM9CY1@stanley.mountain>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Dan Carpenter

drivers/scsi/libfc/fc_fcp.c

@@ -503,7 +503,7 @@ static void fc_fcp_recv_data(struct fc_fcp_pkt *fsp, struct fc_frame *fp)
 		host_bcode = FC_ERROR;
 		goto err;
 	}
-	if (offset + len > fsp->data_len) {
+	if (size_add(offset, len) > fsp->data_len) {
 		/* this should never happen */
 		if ((fr_flags(fp) & FCPHF_CRC_UNCHECKED) &&
 		    fc_frame_crc_check(fp))