* [PATCH net] netfilter: nft_synproxy: stop bypassing the priv->info snapshot
@ 2026-06-11 4:21 Runyu Xiao
2026-06-11 8:15 ` Fernando Fernandez Mancera
2026-06-11 9:49 ` Pablo Neira Ayuso
0 siblings, 2 replies; 3+ messages in thread
From: Runyu Xiao @ 2026-06-11 4:21 UTC (permalink / raw)
To: pablo, fw, netfilter-devel
Cc: coreteam, phil, davem, edumazet, kuba, pabeni, horms, ffmancera,
netdev, linux-kernel, stable, jianhao.xu, Runyu Xiao
nft_synproxy_eval_v4() and nft_synproxy_eval_v6() already take a
whole-object READ_ONCE() snapshot of the shared priv->info state before
building the SYNACK reply, but nft_synproxy_tcp_options() still masks
opts->options with priv->info.options from the live shared object.
When a named synproxy object is updated concurrently with SYN traffic,
the eval path can then mix mss and timestamp handling from the local
snapshot with an options mask taken from a newer configuration, so one
SYNACK no longer reflects a coherent synproxy configuration.
Use info->options so nft_synproxy_tcp_options() stays on the same local
snapshot that the eval path already copied from priv->info.
Fixes: ee394f96ad75 ("netfilter: nft_synproxy: add synproxy stateful object support")
Cc: stable@vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
---
net/netfilter/nft_synproxy.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/net/netfilter/nft_synproxy.c b/net/netfilter/nft_synproxy.c
index 7641f249614c..9ed288c9d168 100644
--- a/net/netfilter/nft_synproxy.c
+++ b/net/netfilter/nft_synproxy.c
@@ -24,14 +24,13 @@ static const struct nla_policy nft_synproxy_policy[NFTA_SYNPROXY_MAX + 1] = {
static void nft_synproxy_tcp_options(struct synproxy_options *opts,
const struct tcphdr *tcp,
struct synproxy_net *snet,
- struct nf_synproxy_info *info,
- const struct nft_synproxy *priv)
+ struct nf_synproxy_info *info)
{
this_cpu_inc(snet->stats->syn_received);
if (tcp->ece && tcp->cwr)
opts->options |= NF_SYNPROXY_OPT_ECN;
- opts->options &= priv->info.options;
+ opts->options &= info->options;
opts->mss_encode = opts->mss_option;
opts->mss_option = info->mss;
if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
@@ -56,7 +55,7 @@ static void nft_synproxy_eval_v4(const struct nft_synproxy *priv,
if (tcp->syn) {
/* Initial SYN from client */
- nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
+ nft_synproxy_tcp_options(opts, tcp, snet, &info);
synproxy_send_client_synack(net, skb, tcp, opts);
consume_skb(skb);
regs->verdict.code = NF_STOLEN;
@@ -87,7 +86,7 @@ static void nft_synproxy_eval_v6(const struct nft_synproxy *priv,
if (tcp->syn) {
/* Initial SYN from client */
- nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
+ nft_synproxy_tcp_options(opts, tcp, snet, &info);
synproxy_send_client_synack_ipv6(net, skb, tcp, opts);
consume_skb(skb);
regs->verdict.code = NF_STOLEN;
--
2.34.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH net] netfilter: nft_synproxy: stop bypassing the priv->info snapshot
2026-06-11 4:21 [PATCH net] netfilter: nft_synproxy: stop bypassing the priv->info snapshot Runyu Xiao
@ 2026-06-11 8:15 ` Fernando Fernandez Mancera
2026-06-11 9:49 ` Pablo Neira Ayuso
1 sibling, 0 replies; 3+ messages in thread
From: Fernando Fernandez Mancera @ 2026-06-11 8:15 UTC (permalink / raw)
To: Runyu Xiao, pablo, fw, netfilter-devel
Cc: coreteam, phil, davem, edumazet, kuba, pabeni, horms, ffmancera,
netdev, linux-kernel, stable, jianhao.xu
On 6/11/26 6:21 AM, Runyu Xiao wrote:
> nft_synproxy_eval_v4() and nft_synproxy_eval_v6() already take a
> whole-object READ_ONCE() snapshot of the shared priv->info state before
> building the SYNACK reply, but nft_synproxy_tcp_options() still masks
> opts->options with priv->info.options from the live shared object.
>
> When a named synproxy object is updated concurrently with SYN traffic,
> the eval path can then mix mss and timestamp handling from the local
> snapshot with an options mask taken from a newer configuration, so one
> SYNACK no longer reflects a coherent synproxy configuration.
>
> Use info->options so nft_synproxy_tcp_options() stays on the same local
> snapshot that the eval path already copied from priv->info.
>
> Fixes: ee394f96ad75 ("netfilter: nft_synproxy: add synproxy stateful object support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Thanks!
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH net] netfilter: nft_synproxy: stop bypassing the priv->info snapshot
2026-06-11 4:21 [PATCH net] netfilter: nft_synproxy: stop bypassing the priv->info snapshot Runyu Xiao
2026-06-11 8:15 ` Fernando Fernandez Mancera
@ 2026-06-11 9:49 ` Pablo Neira Ayuso
1 sibling, 0 replies; 3+ messages in thread
From: Pablo Neira Ayuso @ 2026-06-11 9:49 UTC (permalink / raw)
To: Runyu Xiao
Cc: fw, netfilter-devel, coreteam, phil, davem, edumazet, kuba,
pabeni, horms, ffmancera, netdev, linux-kernel, stable,
jianhao.xu
Hi,
On Thu, Jun 11, 2026 at 12:21:20PM +0800, Runyu Xiao wrote:
> nft_synproxy_eval_v4() and nft_synproxy_eval_v6() already take a
> whole-object READ_ONCE() snapshot of the shared priv->info state before
> building the SYNACK reply, but nft_synproxy_tcp_options() still masks
> opts->options with priv->info.options from the live shared object.
>
> When a named synproxy object is updated concurrently with SYN traffic,
> the eval path can then mix mss and timestamp handling from the local
> snapshot with an options mask taken from a newer configuration, so one
> SYNACK no longer reflects a coherent synproxy configuration.
>
> Use info->options so nft_synproxy_tcp_options() stays on the same local
> snapshot that the eval path already copied from priv->info.
I'll incorporate this to nf-next, this is good for correctness, but no
crash is associated.
> Fixes: ee394f96ad75 ("netfilter: nft_synproxy: add synproxy stateful object support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
> ---
> net/netfilter/nft_synproxy.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/net/netfilter/nft_synproxy.c b/net/netfilter/nft_synproxy.c
> index 7641f249614c..9ed288c9d168 100644
> --- a/net/netfilter/nft_synproxy.c
> +++ b/net/netfilter/nft_synproxy.c
> @@ -24,14 +24,13 @@ static const struct nla_policy nft_synproxy_policy[NFTA_SYNPROXY_MAX + 1] = {
> static void nft_synproxy_tcp_options(struct synproxy_options *opts,
> const struct tcphdr *tcp,
> struct synproxy_net *snet,
> - struct nf_synproxy_info *info,
> - const struct nft_synproxy *priv)
> + struct nf_synproxy_info *info)
> {
> this_cpu_inc(snet->stats->syn_received);
> if (tcp->ece && tcp->cwr)
> opts->options |= NF_SYNPROXY_OPT_ECN;
>
> - opts->options &= priv->info.options;
> + opts->options &= info->options;
> opts->mss_encode = opts->mss_option;
> opts->mss_option = info->mss;
> if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
> @@ -56,7 +55,7 @@ static void nft_synproxy_eval_v4(const struct nft_synproxy *priv,
>
> if (tcp->syn) {
> /* Initial SYN from client */
> - nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
> + nft_synproxy_tcp_options(opts, tcp, snet, &info);
> synproxy_send_client_synack(net, skb, tcp, opts);
> consume_skb(skb);
> regs->verdict.code = NF_STOLEN;
> @@ -87,7 +86,7 @@ static void nft_synproxy_eval_v6(const struct nft_synproxy *priv,
>
> if (tcp->syn) {
> /* Initial SYN from client */
> - nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
> + nft_synproxy_tcp_options(opts, tcp, snet, &info);
> synproxy_send_client_synack_ipv6(net, skb, tcp, opts);
> consume_skb(skb);
> regs->verdict.code = NF_STOLEN;
> --
> 2.34.1
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-06-11 8:15 ` Fernando Fernandez Mancera
2026-06-11 9:49 ` Pablo Neira Ayuso
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