connector: use nlmsg_len() to check message length

[ Upstream commit 162b2bed ]

The current code tests the length of the whole netlink message to be
at least as long to fit a cn_msg. This is wrong as nlmsg_len includes
the length of the netlink message header. Use nlmsg_len() instead to
fix this "off-by-NLMSG_HDRLEN" size check.

Cc: stable@vger.kernel.org  # v2.6.14+
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/connector/connector.c

@@ -157,17 +157,18 @@ static int cn_call_callback(struct sk_buff *skb)
 static void cn_rx_skb(struct sk_buff *__skb)
 {
 	struct nlmsghdr *nlh;
-	int err;
 	struct sk_buff *skb;
+	int len, err;
 
 	skb = skb_get(__skb);
 
 	if (skb->len >= NLMSG_SPACE(0)) {
 		nlh = nlmsg_hdr(skb);
+		len = nlmsg_len(nlh);
 
-		if (nlh->nlmsg_len < sizeof(struct cn_msg) ||
+		if (len < (int)sizeof(struct cn_msg) ||
 		    skb->len < nlh->nlmsg_len ||
-		    nlh->nlmsg_len > CONNECTOR_MAX_MSG_SIZE) {
+		    len > CONNECTOR_MAX_MSG_SIZE) {
 			kfree_skb(skb);
 			return;
 		}