netfilter: nat: add dependencies on conntrack module

MASQUERADE, S/DNAT and REDIRECT already call functions that depend on the
conntrack module.

However, since the conntrack hooks are now registered in a lazy fashion
(i.e., only when needed) a symbol reference is not enough.

Thus, when something is added to a nat table, make sure that it will see
packets by calling nf_ct_netns_get() which will register the conntrack
hooks in the current netns.

An alternative would be to add these dependencies to the NAT table.

However, that has problems when using non-modular builds -- we might
register e.g. ipv6 conntrack before its initcall has run, leading to NULL
deref crashes since its per-netns storage has not yet been allocated.

Adding the dependency in the modules instead has the advantage that nat
table also does not register its hooks until rules are added.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 17 insertions, 1 deletions

diff --git a/net/netfilter/xt_nat.c b/net/netfilter/xt_nat.c
index bea7464cc43f..8107b3eb865f 100644
--- a/net/netfilter/xt_nat.c
+++ b/net/netfilter/xt_nat.c
@@ -23,7 +23,17 @@ static int xt_nat_checkentry_v0(const struct xt_tgchk_param *par)
 			par->target->name);
 		return -EINVAL;
 	}
-	return 0;
+	return nf_ct_netns_get(par->net, par->family);
+}
+
+static int xt_nat_checkentry(const struct xt_tgchk_param *par)
+{
+	return nf_ct_netns_get(par->net, par->family);
+}
+
+static void xt_nat_destroy(const struct xt_tgdtor_param *par)
+{
+	nf_ct_netns_put(par->net, par->family);
 }
 
 static void xt_nat_convert_range(struct nf_nat_range *dst,
@@ -106,6 +116,7 @@ static struct xt_target xt_nat_target_reg[] __read_mostly = {
 		.name		= "SNAT",
 		.revision	= 0,
 		.checkentry	= xt_nat_checkentry_v0,
+		.destroy	= xt_nat_destroy,
 		.target		= xt_snat_target_v0,
 		.targetsize	= sizeof(struct nf_nat_ipv4_multi_range_compat),
 		.family		= NFPROTO_IPV4,
@@ -118,6 +129,7 @@ static struct xt_target xt_nat_target_reg[] __read_mostly = {
 		.name		= "DNAT",
 		.revision	= 0,
 		.checkentry	= xt_nat_checkentry_v0,
+		.destroy	= xt_nat_destroy,
 		.target		= xt_dnat_target_v0,
 		.targetsize	= sizeof(struct nf_nat_ipv4_multi_range_compat),
 		.family		= NFPROTO_IPV4,
@@ -129,6 +141,8 @@ static struct xt_target xt_nat_target_reg[] __read_mostly = {
 	{
 		.name		= "SNAT",
 		.revision	= 1,
+		.checkentry	= xt_nat_checkentry,
+		.destroy	= xt_nat_destroy,
 		.target		= xt_snat_target_v1,
 		.targetsize	= sizeof(struct nf_nat_range),
 		.table		= "nat",
@@ -139,6 +153,8 @@ static struct xt_target xt_nat_target_reg[] __read_mostly = {
 	{
 		.name		= "DNAT",
 		.revision	= 1,
+		.checkentry	= xt_nat_checkentry,
+		.destroy	= xt_nat_destroy,
 		.target		= xt_dnat_target_v1,
 		.targetsize	= sizeof(struct nf_nat_range),
 		.table		= "nat",