tipc: check for null after calling kmemdup

kmemdup can return a null pointer so need to check for it, otherwise
the null key will be dereferenced later in tipc_crypto_key_xmit as
can be seen in the trace [1].

Cc: tipc-discussion@lists.sourceforge.net
Cc: stable@vger.kernel.org # 5.15, 5.14, 5.10

[1] https://syzkaller.appspot.com/bug?id=bca180abb29567b189efdbdb34cbf7ba851c2a58Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Acked-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Link: https://lore.kernel.org/r/20211115160143.5099-1-tadeusz.struk@linaro.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/tipc/crypto.c

@@ -597,6 +597,10 @@ static int tipc_aead_init(struct tipc_aead **aead, struct tipc_aead_key *ukey,
 	tmp->cloned = NULL;
 	tmp->authsize = TIPC_AES_GCM_TAG_SIZE;
 	tmp->key = kmemdup(ukey, tipc_aead_key_size(ukey), GFP_KERNEL);
+	if (!tmp->key) {
+		tipc_aead_free(&tmp->rcu);
+		return -ENOMEM;
+	}
 	memcpy(&tmp->salt, ukey->key + keylen, TIPC_AES_GCM_SALT_SIZE);
 	atomic_set(&tmp->users, 0);
 	atomic64_set(&tmp->seqno, 0);