sctp: add verification checks to SCTP_AUTH_KEY option

The structure used for SCTP_AUTH_KEY option contains a
length that needs to be verfied to prevent buffer overflow
conditions.  Spoted by Eugene Teo <eteo@redhat.com>.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index 675a5c3..1fcb4cf 100644
--- a/net/sctp/auth.c
+++ b/net/sctp/auth.c
@@ -80,6 +80,10 @@
 {
 	struct sctp_auth_bytes *key;
 
+	/* Verify that we are not going to overflow INT_MAX */
+	if ((INT_MAX - key_len) < sizeof(struct sctp_auth_bytes))
+		return NULL;
+
 	/* Allocate the shared key */
 	key = kmalloc(sizeof(struct sctp_auth_bytes) + key_len, gfp);
 	if (!key)