net: ax25: fix information leak to userland

Sometimes ax25_getname() doesn't initialize all members of fsa_digipeater
field of fsa struct, also the struct has padding bytes between
sax25_call and sax25_ndigis fields.  This structure is then copied to
userland.  It leads to leaking of contents of kernel stack memory.
Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ax25/af_ax25.c

@@ -1392,6 +1392,7 @@ static int ax25_getname(struct socket *sock, struct sockaddr *uaddr,
 	ax25_cb *ax25;
 	int err = 0;
 
+	memset(fsa, 0, sizeof(fsa));
 	lock_sock(sk);
 	ax25 = ax25_sk(sk);
 
@@ -1403,7 +1404,6 @@ static int ax25_getname(struct socket *sock, struct sockaddr *uaddr,
 
 		fsa->fsa_ax25.sax25_family = AF_AX25;
 		fsa->fsa_ax25.sax25_call   = ax25->dest_addr;
-		fsa->fsa_ax25.sax25_ndigis = 0;
 
 		if (ax25->digipeat != NULL) {
 			ndigi = ax25->digipeat->ndigi;