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netfilter: nft_synproxy: stop bypassing the priv->info snapshot

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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: ee394f96ad ("netfilter: nft_synproxy: add synproxy stateful object support")
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Runyu Xiao
2026-06-11 12:21:20 +08:00
committed by Pablo Neira Ayuso
parent 22f9dbed18
commit 11d4bc4e26
1 changed files with 4 additions and 5 deletions
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9
net/netfilter/nft_synproxy.c
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@@ -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;