[PATCH net 0/3] netfilter: updates for net

[PATCH net 0/3] netfilter: updates for net

[Florian Westphal]

Hi,

The following patchset contains Netfilter fixes for *net*:

1) its not possible to attach conntrack labels via ctnetlink
   unless one creates a dummy 'ct labels set' rule in nftables.
   This is an oversight, the 'ruleset tests presence, userspace
   (netlink) sets' use-case is valid and should 'just work'.
   Always broken since this got added in Linux 4.7.

2) nft_connlimit reads count value without holding the relevant
   lock, add a READ_ONCE annotation.  From Fernando Fernandez Mancera.

3) There is a long-standing bug (since 4.12) in nftables helper infra
   when NAT is in use: if the helper gets assigned after the nat binding
   was set up, we fail to initialise the 'seqadj' extension, which is
   needed in case NAT payload rewrites need to add (or remove) from the
   packet payload.  Fix from Andrii Melnychenko.

Please, pull these changes from:
The following changes since commit 8df206f7b63611dbaeb8628661d87fe994dcdf71:

  Merge branch 'bug-fixes-for-the-hibmcge-ethernet-driver' (2025-10-28 19:11:07 -0700)

are available in the Git repository at:

  https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf.git tags/nf-25-10-29

for you to fetch changes up to 90918e3b6404c2a37837b8f11692471b4c512de2:

  netfilter: nft_ct: add seqadj extension for natted connections (2025-10-29 14:47:59 +0100)

----------------------------------------------------------------
netfilter pull request nf-25-10-29

----------------------------------------------------------------

Andrii Melnychenko (1):
  netfilter: nft_ct: add seqadj extension for natted connections

Fernando Fernandez Mancera (1):
  netfilter: nft_connlimit: fix possible data race on connection count

Florian Westphal (1):
  netfilter: nft_ct: enable labels for get case too

 net/netfilter/nft_connlimit.c |  2 +-
 net/netfilter/nft_ct.c        | 30 +++++++++++++++++++++++++++---
 2 files changed, 28 insertions(+), 4 deletions(-)

-- 
2.51.0

[PATCH net 1/3] netfilter: nft_ct: enable labels for get case too

[Florian Westphal]

conntrack labels can only be set when the conntrack has been created
with the "ctlabel" extension.

For older iptables (connlabel match), adding an "-m connlabel" rule
turns on the ctlabel extension allocation for all future conntrack
entries.

For nftables, its only enabled for 'ct label set foo', but not for
'ct label foo' (i.e. check).
But users could have a ruleset that only checks for presence, and rely
on userspace to set a label bit via ctnetlink infrastructure.

This doesn't work without adding a dummy 'ct label set' rule.
We could also enable extension infra for the first (failing) ctnetlink
request, but unlike ruleset we would not be able to disable the
extension again.

Therefore turn on ctlabel extension allocation if an nftables ruleset
checks for a connlabel too.

Fixes: 1ad8f48df6f6 ("netfilter: nftables: add connlabel set support")
Reported-by: Antonio Ojea <aojea@google.com>
Closes: https://lore.kernel.org/netfilter-devel/aPi_VdZpVjWujZ29@strlen.de/
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nft_ct.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_ct.c b/net/netfilter/nft_ct.c
index d526e69a2a2b..a418eb3d612b 100644
--- a/net/netfilter/nft_ct.c
+++ b/net/netfilter/nft_ct.c
@@ -379,6 +379,14 @@ static bool nft_ct_tmpl_alloc_pcpu(void)
 }
 #endif
 
+static void __nft_ct_get_destroy(const struct nft_ctx *ctx, struct nft_ct *priv)
+{
+#ifdef CONFIG_NF_CONNTRACK_LABELS
+	if (priv->key == NFT_CT_LABELS)
+		nf_connlabels_put(ctx->net);
+#endif
+}
+
 static int nft_ct_get_init(const struct nft_ctx *ctx,
 			   const struct nft_expr *expr,
 			   const struct nlattr * const tb[])
@@ -413,6 +421,10 @@ static int nft_ct_get_init(const struct nft_ctx *ctx,
 		if (tb[NFTA_CT_DIRECTION] != NULL)
 			return -EINVAL;
 		len = NF_CT_LABELS_MAX_SIZE;
+
+		err = nf_connlabels_get(ctx->net, (len * BITS_PER_BYTE) - 1);
+		if (err)
+			return err;
 		break;
 #endif
 	case NFT_CT_HELPER:
@@ -494,7 +506,8 @@ static int nft_ct_get_init(const struct nft_ctx *ctx,
 		case IP_CT_DIR_REPLY:
 			break;
 		default:
-			return -EINVAL;
+			err = -EINVAL;
+			goto err;
 		}
 	}
 
@@ -502,11 +515,11 @@ static int nft_ct_get_init(const struct nft_ctx *ctx,
 	err = nft_parse_register_store(ctx, tb[NFTA_CT_DREG], &priv->dreg, NULL,
 				       NFT_DATA_VALUE, len);
 	if (err < 0)
-		return err;
+		goto err;
 
 	err = nf_ct_netns_get(ctx->net, ctx->family);
 	if (err < 0)
-		return err;
+		goto err;
 
 	if (priv->key == NFT_CT_BYTES ||
 	    priv->key == NFT_CT_PKTS  ||
@@ -514,6 +527,9 @@ static int nft_ct_get_init(const struct nft_ctx *ctx,
 		nf_ct_set_acct(ctx->net, true);
 
 	return 0;
+err:
+	__nft_ct_get_destroy(ctx, priv);
+	return err;
 }
 
 static void __nft_ct_set_destroy(const struct nft_ctx *ctx, struct nft_ct *priv)
@@ -626,6 +642,9 @@ static int nft_ct_set_init(const struct nft_ctx *ctx,
 static void nft_ct_get_destroy(const struct nft_ctx *ctx,
 			       const struct nft_expr *expr)
 {
+	struct nft_ct *priv = nft_expr_priv(expr);
+
+	__nft_ct_get_destroy(ctx, priv);
 	nf_ct_netns_put(ctx->net, ctx->family);
 }
 
-- 
2.51.0

Re: [PATCH net 1/3] netfilter: nft_ct: enable labels for get case too

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Florian Westphal <fw@strlen.de>:

On Wed, 29 Oct 2025 14:56:15 +0100 you wrote:
> conntrack labels can only be set when the conntrack has been created
> with the "ctlabel" extension.
> 
> For older iptables (connlabel match), adding an "-m connlabel" rule
> turns on the ctlabel extension allocation for all future conntrack
> entries.
> 
> [...]

Here is the summary with links:
  - [net,1/3] netfilter: nft_ct: enable labels for get case too
    https://git.kernel.org/netdev/net/c/514f1dc8f2ca
  - [net,2/3] netfilter: nft_connlimit: fix possible data race on connection count
    https://git.kernel.org/netdev/net/c/8d96dfdcabef
  - [net,3/3] netfilter: nft_ct: add seqadj extension for natted connections
    https://git.kernel.org/netdev/net/c/90918e3b6404

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

[PATCH net 2/3] netfilter: nft_connlimit: fix possible data race on connection count

[Florian Westphal]

From: Fernando Fernandez Mancera <fmancera@suse.de>

nft_connlimit_eval() reads priv->list->count to check if the connection
limit has been exceeded. This value is being read without a lock and can
be modified by a different process. Use READ_ONCE() for correctness.

Fixes: df4a90250976 ("netfilter: nf_conncount: merge lookup and add functions")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nft_connlimit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nft_connlimit.c b/net/netfilter/nft_connlimit.c
index 92b984fa8175..fc35a11cdca2 100644
--- a/net/netfilter/nft_connlimit.c
+++ b/net/netfilter/nft_connlimit.c
@@ -48,7 +48,7 @@ static inline void nft_connlimit_do_eval(struct nft_connlimit *priv,
 		return;
 	}
 
-	count = priv->list->count;
+	count = READ_ONCE(priv->list->count);
 
 	if ((count > priv->limit) ^ priv->invert) {
 		regs->verdict.code = NFT_BREAK;
-- 
2.51.0

[PATCH net 3/3] netfilter: nft_ct: add seqadj extension for natted connections

[Florian Westphal]

From: Andrii Melnychenko <a.melnychenko@vyos.io>

Sequence adjustment may be required for FTP traffic with PASV/EPSV modes.
due to need to re-write packet payload (IP, port) on the ftp control
connection. This can require changes to the TCP length and expected
seq / ack_seq.

The easiest way to reproduce this issue is with PASV mode.
Example ruleset:
table inet ftp_nat {
        ct helper ftp_helper {
                type "ftp" protocol tcp
                l3proto inet
        }

        chain prerouting {
                type filter hook prerouting priority 0; policy accept;
                tcp dport 21 ct state new ct helper set "ftp_helper"
        }
}
table ip nat {
        chain prerouting {
                type nat hook prerouting priority -100; policy accept;
                tcp dport 21 dnat ip prefix to ip daddr map {
			192.168.100.1 : 192.168.13.2/32 }
        }

        chain postrouting {
                type nat hook postrouting priority 100 ; policy accept;
                tcp sport 21 snat ip prefix to ip saddr map {
			192.168.13.2 : 192.168.100.1/32 }
        }
}

Note that the ftp helper gets assigned *after* the dnat setup.

The inverse (nat after helper assign) is handled by an existing
check in nf_nat_setup_info() and will not show the problem.

Topoloy:

 +-------------------+     +----------------------------------+
 | FTP: 192.168.13.2 | <-> | NAT: 192.168.13.3, 192.168.100.1 |
 +-------------------+     +----------------------------------+
                                      |
                         +-----------------------+
                         | Client: 192.168.100.2 |
                         +-----------------------+

ftp nat changes do not work as expected in this case:
Connected to 192.168.100.1.
[..]
ftp> epsv
EPSV/EPRT on IPv4 off.
ftp> ls
227 Entering passive mode (192,168,100,1,209,129).
421 Service not available, remote server has closed connection.

Kernel logs:
Missing nfct_seqadj_ext_add() setup call
WARNING: CPU: 1 PID: 0 at net/netfilter/nf_conntrack_seqadj.c:41
[..]
 __nf_nat_mangle_tcp_packet+0x100/0x160 [nf_nat]
 nf_nat_ftp+0x142/0x280 [nf_nat_ftp]
 help+0x4d1/0x880 [nf_conntrack_ftp]
 nf_confirm+0x122/0x2e0 [nf_conntrack]
 nf_hook_slow+0x3c/0xb0
 ..

Fix this by adding the required extension when a conntrack helper is assigned
to a connection that has a nat binding.

Fixes: 1a64edf54f55 ("netfilter: nft_ct: add helper set support")
Signed-off-by: Andrii Melnychenko <a.melnychenko@vyos.io>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nft_ct.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/netfilter/nft_ct.c b/net/netfilter/nft_ct.c
index a418eb3d612b..6f2ae7cad731 100644
--- a/net/netfilter/nft_ct.c
+++ b/net/netfilter/nft_ct.c
@@ -22,6 +22,7 @@
 #include <net/netfilter/nf_conntrack_timeout.h>
 #include <net/netfilter/nf_conntrack_l4proto.h>
 #include <net/netfilter/nf_conntrack_expect.h>
+#include <net/netfilter/nf_conntrack_seqadj.h>
 
 struct nft_ct_helper_obj  {
 	struct nf_conntrack_helper *helper4;
@@ -1192,6 +1193,10 @@ static void nft_ct_helper_obj_eval(struct nft_object *obj,
 	if (help) {
 		rcu_assign_pointer(help->helper, to_assign);
 		set_bit(IPS_HELPER_BIT, &ct->status);
+
+		if ((ct->status & IPS_NAT_MASK) && !nfct_seqadj(ct))
+			if (!nfct_seqadj_ext_add(ct))
+				regs->verdict.code = NF_DROP;
 	}
 }
 
-- 
2.51.0