af_key: Do not call xfrm_probe_algs in parallel

When namespace support was added to xfrm/afkey, it caused the
previously single-threaded call to xfrm_probe_algs to become
multi-threaded.  This is buggy and needs to be fixed with a mutex.
Reported-by: Abhishek Shah <abhishek.shah@columbia.edu>
Fixes: 283bc9f3 ("xfrm: Namespacify xfrm state/policy locks")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/key/af_key.c

@@ -1697,9 +1697,12 @@ static int pfkey_register(struct sock *sk, struct sk_buff *skb, const struct sad
 		pfk->registered |= (1<<hdr->sadb_msg_satype);
 	}
 
+	mutex_lock(&pfkey_mutex);
 	xfrm_probe_algs();
 
 	supp_skb = compose_sadb_supported(hdr, GFP_KERNEL | __GFP_ZERO);
+	mutex_unlock(&pfkey_mutex);
+
 	if (!supp_skb) {
 		if (hdr->sadb_msg_satype != SADB_SATYPE_UNSPEC)
 			pfk->registered &= ~(1<<hdr->sadb_msg_satype);