[PATCH] nbd: Check magic before doing anything else

We should check magic sequence in reply packet before trying to find
request with it's request handle.  This also solves the problem with
"Unexpected reply" message beeing logged, when packet with invalid magic is
received.
Signed-off-by: Michal Feix <michal@feix.cz>
Acked-by: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/block/nbd.c

@@ -300,6 +300,15 @@ static struct request *nbd_read_stat(struct nbd_device *lo)
 				lo->disk->disk_name, result);
 		goto harderror;
 	}
+
+	if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
+		printk(KERN_ERR "%s: Wrong magic (0x%lx)\n",
+				lo->disk->disk_name,
+				(unsigned long)ntohl(reply.magic));
+		result = -EPROTO;
+		goto harderror;
+	}
+
 	req = nbd_find_request(lo, reply.handle);
 	if (unlikely(IS_ERR(req))) {
 		result = PTR_ERR(req);
@@ -312,13 +321,6 @@ static struct request *nbd_read_stat(struct nbd_device *lo)
 		goto harderror;
 	}
 
-	if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
-		printk(KERN_ERR "%s: Wrong magic (0x%lx)\n",
-				lo->disk->disk_name,
-				(unsigned long)ntohl(reply.magic));
-		result = -EPROTO;
-		goto harderror;
-	}
 	if (ntohl(reply.error)) {
 		printk(KERN_ERR "%s: Other side returned error (%d)\n",
 				lo->disk->disk_name, ntohl(reply.error));