[SRU][J][PATCH 1/1] netfilter: nf_conntrack_expect: use expect->helper

[Cengiz Can]

From: Pablo Neira Ayuso <pablo at netfilter.org>

Use expect->helper in ctnetlink and /proc to dump the helper name.
Using nfct_help() without holding a reference to the master conntrack
is unsafe.

Use exp->master->helper in ctnetlink path if userspace does not provide
an explicit helper when creating an expectation to retain the existing
behaviour. The ctnetlink expectation path holds the reference on the
master conntrack and nf_conntrack_expect lock and the nfnetlink glue
path refers to the master ct that is attached to the skb.

Reported-by: Hyunwoo Kim <imv4bel at gmail.com>
Signed-off-by: Florian Westphal <fw at strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo at netfilter.org>
(backported from commit f01794106042ee27e54af6fdf5b319a2fe3df94d)
[bot_kybele: backported to jammy; review and refine this note]
CVE-2026-31414
Assisted-by: kybele:claude-opus-4.8
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 net/netfilter/nf_conntrack_netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 2e8fb88e9a6a..ecce2cecc5ad 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -3581,7 +3581,7 @@ ctnetlink_alloc_expect(const struct nlattr * const cda[], struct nf_conn *ct,
 	exp->master = ct;
 	if (!helper)
 		helper = rcu_dereference(help->helper);
-	exp->helper = helper;
+	rcu_assign_pointer(exp->helper, helper);
 	exp->tuple = *tuple;
 	exp->mask.src.u3 = mask->src.u3;
 	exp->mask.src.u.all = mask->src.u.all;
-- 
2.43.0