x25: Prevent skb overreads when checking call user data

x25_find_listener does not check that the amount of call user data given
in the skb is big enough in per-socket comparisons, hence buffer
overreads may occur.  Fix this by adding a check.

Signed-off-by: Matthew Daley <mattjd@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Andrew Hendry <andrew.hendry@gmail.com>
Cc: stable <stable@kernel.org>
Acked-by: Andrew Hendry <andrew.hendry@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index aa567b09ea9a..5f03e4ea65bf 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -295,7 +295,8 @@ static struct sock *x25_find_listener(struct x25_address *addr,
                          * Found a listening socket, now check the incoming
                          * call user data vs this sockets call user data
                          */
-                        if(skb->len > 0 && x25_sk(s)->cudmatchlength > 0) {
+                        if (x25_sk(s)->cudmatchlength > 0 &&
+                                skb->len >= x25_sk(s)->cudmatchlength) {
                                 if((memcmp(x25_sk(s)->calluserdata.cuddata,
                                         skb->data,
                                         x25_sk(s)->cudmatchlength)) == 0) {