UPSTREAM: xfrm_user: validate XFRM_MSG_NEWAE incoming ESN size harder

Kees Cook has pointed out that xfrm_replay_state_esn_len() is subject to
wrapping issues.  To ensure we are correctly ensuring that the two ESN
structures are the same size compare both the overall size as reported
by xfrm_replay_state_esn_len() and the internal length are the same.

CVE-2017-7184
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrey Ulanov <andreyu@google.com>

(chery picked from f843ee6dd019bcece3e74e76ad9df0155655d0df)

BUG=b:36733546
TEST=kernel compiles

Change-Id: Ifc49ff10d8e8ed8337fa61b5a7129db569892e89
Reviewed-on: https://chromium-review.googlesource.com/462459
Commit-Ready: Andrey Ulanov <andreyu@google.com>
Tested-by: Andrey Ulanov <andreyu@google.com>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 5a3b125..d448ab3 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -412,7 +412,11 @@
 	up = nla_data(rp);
 	ulen = xfrm_replay_state_esn_len(up);
 
-	if (nla_len(rp) < ulen || xfrm_replay_state_esn_len(replay_esn) != ulen)
+	/* Check the overall length and the internal bitmap length to avoid
+	 * potential overflow. */
+	if (nla_len(rp) < ulen ||
+	    xfrm_replay_state_esn_len(replay_esn) != ulen ||
+	    replay_esn->bmp_len != up->bmp_len)
 		return -EINVAL;
 
 	if (up->replay_window > up->bmp_len * sizeof(__u32) * 8)