netfilter: core: only allow one nat hook per hook point

The netfilter NAT core cannot deal with more than one NAT hook per hook
location (prerouting, input ...), because the NAT hooks install a NAT null
binding in case the iptables nat table (iptable_nat hooks) or the
corresponding nftables chain (nft nat hooks) doesn't specify a nat
transformation.

Null bindings are needed to detect port collsisions between NAT-ed and
non-NAT-ed connections.

This causes nftables NAT rules to not work when iptable_nat module is
loaded, and vice versa because nat binding has already been attached
when the second nat hook is consulted.

The netfilter core is not really the correct location to handle this
(hooks are just hooks, the core has no notion of what kinds of side
 effects a hook implements), but its the only place where we can check
for conflicts between both iptables hooks and nftables hooks without
adding dependencies.

So add nat annotation to hook_ops to describe those hooks that will
add NAT bindings and then make core reject if such a hook already exists.
The annotation fills a padding hole, in case further restrictions appar
we might change this to a 'u8 type' instead of bool.

iptables error if nft nat hook active:
iptables -t nat -A POSTROUTING -j MASQUERADE
iptables v1.4.21: can't initialize iptables table `nat': File exists
Perhaps iptables or your kernel needs to be upgraded.

nftables error if iptables nat table present:
nft -f /etc/nftables/ipv4-nat
/usr/etc/nftables/ipv4-nat:3:1-2: Error: Could not process rule: File exists
table nat {
^^

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2017-12-08 17:01:54 +01:00 committed by Pablo Neira Ayuso
parent 03d13b6868
commit f92b40a8b2
5 changed files with 17 additions and 0 deletions

View File

@ -67,6 +67,7 @@ struct nf_hook_ops {
struct net_device *dev;
void *priv;
u_int8_t pf;
bool nat_hook;
unsigned int hooknum;
/* Hooks are ordered in ascending priority. */
int priority;

View File

@ -72,6 +72,7 @@ static const struct nf_hook_ops nf_nat_ipv4_ops[] = {
{
.hook = iptable_nat_ipv4_in,
.pf = NFPROTO_IPV4,
.nat_hook = true,
.hooknum = NF_INET_PRE_ROUTING,
.priority = NF_IP_PRI_NAT_DST,
},
@ -79,6 +80,7 @@ static const struct nf_hook_ops nf_nat_ipv4_ops[] = {
{
.hook = iptable_nat_ipv4_out,
.pf = NFPROTO_IPV4,
.nat_hook = true,
.hooknum = NF_INET_POST_ROUTING,
.priority = NF_IP_PRI_NAT_SRC,
},
@ -86,6 +88,7 @@ static const struct nf_hook_ops nf_nat_ipv4_ops[] = {
{
.hook = iptable_nat_ipv4_local_fn,
.pf = NFPROTO_IPV4,
.nat_hook = true,
.hooknum = NF_INET_LOCAL_OUT,
.priority = NF_IP_PRI_NAT_DST,
},
@ -93,6 +96,7 @@ static const struct nf_hook_ops nf_nat_ipv4_ops[] = {
{
.hook = iptable_nat_ipv4_fn,
.pf = NFPROTO_IPV4,
.nat_hook = true,
.hooknum = NF_INET_LOCAL_IN,
.priority = NF_IP_PRI_NAT_SRC,
},

View File

@ -74,6 +74,7 @@ static const struct nf_hook_ops nf_nat_ipv6_ops[] = {
{
.hook = ip6table_nat_in,
.pf = NFPROTO_IPV6,
.nat_hook = true,
.hooknum = NF_INET_PRE_ROUTING,
.priority = NF_IP6_PRI_NAT_DST,
},
@ -81,6 +82,7 @@ static const struct nf_hook_ops nf_nat_ipv6_ops[] = {
{
.hook = ip6table_nat_out,
.pf = NFPROTO_IPV6,
.nat_hook = true,
.hooknum = NF_INET_POST_ROUTING,
.priority = NF_IP6_PRI_NAT_SRC,
},
@ -88,12 +90,14 @@ static const struct nf_hook_ops nf_nat_ipv6_ops[] = {
{
.hook = ip6table_nat_local_fn,
.pf = NFPROTO_IPV6,
.nat_hook = true,
.hooknum = NF_INET_LOCAL_OUT,
.priority = NF_IP6_PRI_NAT_DST,
},
/* After packet filtering, change source */
{
.hook = ip6table_nat_fn,
.nat_hook = true,
.pf = NFPROTO_IPV6,
.hooknum = NF_INET_LOCAL_IN,
.priority = NF_IP6_PRI_NAT_SRC,

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@ -160,6 +160,12 @@ nf_hook_entries_grow(const struct nf_hook_entries *old,
++i;
continue;
}
if (reg->nat_hook && orig_ops[i]->nat_hook) {
kvfree(new);
return ERR_PTR(-EEXIST);
}
if (inserted || reg->priority > orig_ops[i]->priority) {
new_ops[nhooks] = (void *)orig_ops[i];
new->hooks[nhooks] = old->hooks[i];

View File

@ -1400,6 +1400,8 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask,
ops->hook = hookfn;
if (afi->hook_ops_init)
afi->hook_ops_init(ops, i);
if (basechain->type->type == NFT_CHAIN_T_NAT)
ops->nat_hook = true;
}
chain->flags |= NFT_BASE_CHAIN;