netfilter: ebt_ulog: fix info leaks

The ulog messages leak heap bytes by the means of padding bytes and
incompletely filled string arrays. Fix those by memset(0)'ing the
whole struct before filling it.
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/bridge/netfilter/ebt_ulog.c

@@ -181,6 +181,7 @@ static void ebt_ulog_packet(struct net *net, unsigned int hooknr,
 	ub->qlen++;
 
 	pm = nlmsg_data(nlh);
+	memset(pm, 0, sizeof(*pm));
 
 	/* Fill in the ulog data */
 	pm->version = EBT_ULOG_VERSION;
@@ -193,8 +194,6 @@ static void ebt_ulog_packet(struct net *net, unsigned int hooknr,
 	pm->hook = hooknr;
 	if (uloginfo->prefix != NULL)
 		strcpy(pm->prefix, uloginfo->prefix);
-	else
-		*(pm->prefix) = '\0';
 
 	if (in) {
 		strcpy(pm->physindev, in->name);
@@ -204,16 +203,14 @@ static void ebt_ulog_packet(struct net *net, unsigned int hooknr,
 			strcpy(pm->indev, br_port_get_rcu(in)->br->dev->name);
 		else
 			strcpy(pm->indev, in->name);
-	} else
-		pm->indev[0] = pm->physindev[0] = '\0';
+	}
 
 	if (out) {
 		/* If out exists, then out is a bridge port */
 		strcpy(pm->physoutdev, out->name);
 		/* rcu_read_lock()ed by nf_hook_slow */
 		strcpy(pm->outdev, br_port_get_rcu(out)->br->dev->name);
-	} else
-		pm->outdev[0] = pm->physoutdev[0] = '\0';
+	}
 
 	if (skb_copy_bits(skb, -ETH_HLEN, pm->data, copy_len) < 0)
 		BUG();