This is a note to let you know that I've just added the patch titled

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

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: netfilter-core-only-allow-one-nat-hook-per-hook-point.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Mon Apr 9 10:16:32 CEST 2018

From: Florian Westphal fw@strlen.de Date: Fri, 8 Dec 2017 17:01:54 +0100 Subject: netfilter: core: only allow one nat hook per hook point

From: Florian Westphal fw@strlen.de

[ Upstream commit f92b40a8b2645af38bd6814651c59c1e690db53d ]

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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/netfilter.h | 1 + net/ipv4/netfilter/iptable_nat.c | 4 ++++ net/ipv6/netfilter/ip6table_nat.c | 4 ++++ net/netfilter/core.c | 6 ++++++ net/netfilter/nf_tables_api.c | 2 ++ 5 files changed, 17 insertions(+)

--- a/include/linux/netfilter.h +++ b/include/linux/netfilter.h @@ -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; --- a/net/ipv4/netfilter/iptable_nat.c +++ b/net/ipv4/netfilter/iptable_nat.c @@ -72,6 +72,7 @@ static const struct nf_hook_ops nf_nat_i { .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_i { .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_i { .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_i { .hook = iptable_nat_ipv4_fn, .pf = NFPROTO_IPV4, + .nat_hook = true, .hooknum = NF_INET_LOCAL_IN, .priority = NF_IP_PRI_NAT_SRC, }, --- a/net/ipv6/netfilter/ip6table_nat.c +++ b/net/ipv6/netfilter/ip6table_nat.c @@ -74,6 +74,7 @@ static const struct nf_hook_ops nf_nat_i { .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_i { .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_i { .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, --- a/net/netfilter/core.c +++ b/net/netfilter/core.c @@ -135,6 +135,12 @@ nf_hook_entries_grow(const struct nf_hoo ++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]; --- a/net/netfilter/nf_tables_api.c +++ b/net/netfilter/nf_tables_api.c @@ -1400,6 +1400,8 @@ static int nf_tables_addchain(struct nft 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;

Patches currently in stable-queue which might be from fw@strlen.de are

queue-4.15/netfilter-core-only-allow-one-nat-hook-per-hook-point.patch