x25: Validate incoming call user data lengths

X.25 call user data is being copied in its entirety from incoming messages
without consideration to the size of the destination buffers, leading to
possible buffer overflows. Validate incoming call user data lengths before
these copies are performed.

It appears this issue was noticed some time ago, however nothing seemed to
come of it: see http://www.spinics.net/lists/linux-x25/msg00043.html and
commit 8db09f26f912f7c90c764806e804b558da520d4f.

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

1 files changed, 3 insertions, 0 deletions

diff --git a/net/x25/x25_in.c b/net/x25/x25_in.c
index 0b073b51b183..63488fd4885a 100644
--- a/net/x25/x25_in.c
+++ b/net/x25/x25_in.c
@@ -127,6 +127,9 @@ static int x25_state1_machine(struct sock *sk, struct sk_buff *skb, int frametyp
                  *      Copy any Call User Data.
                  */
                 if (skb->len > 0) {
+                        if (skb->len > X25_MAX_CUD_LEN)
+                                goto out_clear;
+
                         skb_copy_from_linear_data(skb,
                                                   x25->calluserdata.cuddata,
                                                   skb->len);