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

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

commit d90c902449a7561f1b1d58ba5a0d11728ce8b0b2 upstream.

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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>