af_key: Fix slab-out-of-bounds in pfkey_compile_policy.

The sadb_x_sec_len is stored in the unit 'byte divided by eight'.
So we have to multiply this value by eight before we can do
size checks. Otherwise we may get a slab-out-of-bounds when
we memcpy the user sec_ctx.

Fixes: df71837d502 ("[LSM-IPSec]: Security association restriction.")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/key/af_key.c

@@ -3285,7 +3285,7 @@ static struct xfrm_policy *pfkey_compile_policy(struct sock *sk, int opt,
 		p += pol->sadb_x_policy_len*8;
 		sec_ctx = (struct sadb_x_sec_ctx *)p;
 		if (len < pol->sadb_x_policy_len*8 +
-		    sec_ctx->sadb_x_sec_len) {
+		    sec_ctx->sadb_x_sec_len*8) {
 			*dir = -EINVAL;
 			goto out;
 		}