xfrm_user: fix info leak in copy_to_user_auth()

copy_to_user_auth() fails to initialize the remainder of alg_name and
therefore discloses up to 54 bytes of heap memory via netlink to
userland.

Use strncpy() instead of strcpy() to fill the trailing bytes of alg_name
with null bytes.
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/xfrm/xfrm_user.c

@@ -742,7 +742,7 @@ static int copy_to_user_auth(struct xfrm_algo_auth *auth, struct sk_buff *skb)
 		return -EMSGSIZE;
 
 	algo = nla_data(nla);
-	strcpy(algo->alg_name, auth->alg_name);
+	strncpy(algo->alg_name, auth->alg_name, sizeof(algo->alg_name));
 	memcpy(algo->alg_key, auth->alg_key, (auth->alg_key_len + 7) / 8);
 	algo->alg_key_len = auth->alg_key_len;