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[PATCH net 05/14] netfilter: nft_synproxy: stop bypassing the priv->info snapshot

From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: 2026-06-23 22:16:01
Also in: netfilter-devel
Subsystem: netfilter, networking [general], the rest · Maintainers: Pablo Neira Ayuso, Florian Westphal, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds 

From: Runyu Xiao <redacted>

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")
Signed-off-by: Runyu Xiao <redacted>
Reviewed-by: Fernando Fernandez Mancera <redacted>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 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;
-- 
2.47.3
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