netfilter: ipt_CLUSTERIP: fix out-of-bounds accesses in clusterip_tg_check()

Commit 136e92bbec0a switched local_nodes from an array to a bitmask
but did not add proper bounds checks. As the result
clusterip_config_init_nodelist() can both over-read
ipt_clusterip_tgt_info.local_nodes and over-write
clusterip_config.local_nodes.

Add bounds checks for both.

Fixes: 136e92bbec0a ("[NETFILTER] CLUSTERIP: use a bitmap to store node responsibility data")
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/ipt_CLUSTERIP.c

@@ -431,7 +431,7 @@ static int clusterip_tg_check(const struct xt_tgchk_param *par)
 	struct ipt_clusterip_tgt_info *cipinfo = par->targinfo;
 	const struct ipt_entry *e = par->entryinfo;
 	struct clusterip_config *config;
-	int ret;
+	int ret, i;
 
 	if (par->nft_compat) {
 		pr_err("cannot use CLUSTERIP target from nftables compat\n");
@@ -450,8 +450,18 @@ static int clusterip_tg_check(const struct xt_tgchk_param *par)
 		pr_info("Please specify destination IP\n");
 		return -EINVAL;
 	}
-
-	/* FIXME: further sanity checks */
+	if (cipinfo->num_local_nodes > ARRAY_SIZE(cipinfo->local_nodes)) {
+		pr_info("bad num_local_nodes %u\n", cipinfo->num_local_nodes);
+		return -EINVAL;
+	}
+	for (i = 0; i < cipinfo->num_local_nodes; i++) {
+		if (cipinfo->local_nodes[i] - 1 >=
+		    sizeof(config->local_nodes) * 8) {
+			pr_info("bad local_nodes[%d] %u\n",
+				i, cipinfo->local_nodes[i]);
+			return -EINVAL;
+		}
+	}
 
 	config = clusterip_config_find_get(par->net, e->ip.dst.s_addr, 1);
 	if (!config) {