[PATCH 6.19 089/311] netfilter: nf_conntrack_expect: honor expectation helper field

Greg Kroah-Hartman
2026-04-08T18:53:37Z

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

[ Upstream commit 9c42bc9db90a154bc61ae337a070465f3393485a ]

The expectation helper field is mostly unused. As a result, the
netfilter codebase relies on accessing the helper through exp->master.

Always set on the expectation helper field so it can be used to reach
the helper.

nf_ct_expect_init() is called from packet path where the skb owns
the ct object, therefore accessing exp->master for the newly created
expectation is safe. This saves a lot of updates in all callsites
to pass the ct object as parameter to nf_ct_expect_init().

This is a preparation patches for follow up fixes.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Stable-dep-of: 917b61fa2042 ("netfilter: ctnetlink: ignore explicit helper on new expectations")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/netfilter/nf_conntrack_expect.h | 2 +-
net/netfilter/nf_conntrack_broadcast.c | 2 +-
net/netfilter/nf_conntrack_expect.c | 14 +++++++++++++-
net/netfilter/nf_conntrack_h323_main.c | 12 ++++++------
net/netfilter/nf_conntrack_helper.c | 7 ++++++-
net/netfilter/nf_conntrack_netlink.c | 2 +-
net/netfilter/nf_conntrack_sip.c | 2 +-
7 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/include/net/netfilter/nf_conntrack_expect.h b/include/net/netfilter/nf_conntrack_expect.h
index 165e7a03b8e9d..1b01400b10bdb 100644
--- a/include/net/netfilter/nf_conntrack_expect.h
+++ b/include/net/netfilter/nf_conntrack_expect.h
@@ -40,7 +40,7 @@ struct nf_conntrack_expect {
struct nf_conntrack_expect *this);

/* Helper to assign to new connection */
- struct nf_conntrack_helper *helper;
+ struct nf_conntrack_helper __rcu *helper;

/* The conntrack of the master connection */
struct nf_conn *master;
diff --git a/net/netfilter/nf_conntrack_broadcast.c b/net/netfilter/nf_conntrack_broadcast.c
index a7552a46d6acf..1964c596c6468 100644
--- a/net/netfilter/nf_conntrack_broadcast.c
+++ b/net/netfilter/nf_conntrack_broadcast.c
@@ -70,7 +70,7 @@ int nf_conntrack_broadcast_help(struct sk_buff *skb,
exp->expectfn = NULL;
exp->flags = NF_CT_EXPECT_PERMANENT;
exp->class = NF_CT_EXPECT_CLASS_DEFAULT;
- exp->helper = NULL;
+ rcu_assign_pointer(exp->helper, helper);

nf_ct_expect_related(exp, 0);
nf_ct_expect_put(exp);
diff --git a/net/netfilter/nf_conntrack_expect.c b/net/netfilter/nf_conntrack_expect.c
index 227fb5dc39e27..6739b48c644fc 100644
--- a/net/netfilter/nf_conntrack_expect.c
+++ b/net/netfilter/nf_conntrack_expect.c
@@ -309,12 +309,19 @@ struct nf_conntrack_expect *nf_ct_expect_alloc(struct nf_conn *me)
}
EXPORT_SYMBOL_GPL(nf_ct_expect_alloc);

+/* This function can only be used from packet path, where accessing
+ * master's helper is safe, because the packet holds a reference on
+ * the conntrack object. Never use it from control plane.
+ */
void nf_ct_expect_init(struct nf_conntrack_expect *exp, unsigned int class,
u_int8_t family,
const union nf_inet_addr *saddr,
const union nf_inet_addr *daddr,
u_int8_t proto, const __be16 *src, const __be16 *dst)
{
+ struct nf_conntrack_helper *helper = NULL;
+ struct nf_conn *ct = exp->master;
+ struct nf_conn_help *help;
int len;

if (family == AF_INET)
@@ -325,7 +332,12 @@ void nf_ct_expect_init(struct nf_conntrack_expect *exp, unsigned int class,
exp->flags = 0;
exp->class = class;
exp->expectfn = NULL;
- exp->helper = NULL;
+
+ help = nfct_help(ct);
+ if (help)
+ helper = rcu_dereference(help->helper);
+
+ rcu_assign_pointer(exp->helper, helper);
exp->tuple.src.l3num = family;
exp->tuple.dst.protonum = proto;

diff --git a/net/netfilter/nf_conntrack_h323_main.c b/net/netfilter/nf_conntrack_h323_main.c
index e35814d68ce30..bd7e9e13e4f68 100644
--- a/net/netfilter/nf_conntrack_h323_main.c
+++ b/net/netfilter/nf_conntrack_h323_main.c
@@ -642,7 +642,7 @@ static int expect_h245(struct sk_buff *skb, struct nf_conn *ct,
&ct->tuplehash[!dir].tuple.src.u3,
&ct->tuplehash[!dir].tuple.dst.u3,
IPPROTO_TCP, NULL, &port);
- exp->helper = &nf_conntrack_helper_h245;
+ rcu_assign_pointer(exp->helper, &nf_conntrack_helper_h245);

nathook = rcu_dereference(nfct_h323_nat_hook);
if (memcmp(&ct->tuplehash[dir].tuple.src.u3,
@@ -766,7 +766,7 @@ static int expect_callforwarding(struct sk_buff *skb,
nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
&ct->tuplehash[!dir].tuple.src.u3, &addr,
IPPROTO_TCP, NULL, &port);
- exp->helper = nf_conntrack_helper_q931;
+ rcu_assign_pointer(exp->helper, nf_conntrack_helper_q931);

nathook = rcu_dereference(nfct_h323_nat_hook);
if (memcmp(&ct->tuplehash[dir].tuple.src.u3,
@@ -1233,7 +1233,7 @@ static int expect_q931(struct sk_buff *skb, struct nf_conn *ct,
&ct->tuplehash[!dir].tuple.src.u3 : NULL,
&ct->tuplehash[!dir].tuple.dst.u3,
IPPROTO_TCP, NULL, &port);
- exp->helper = nf_conntrack_helper_q931;
+ rcu_assign_pointer(exp->helper, nf_conntrack_helper_q931);
exp->flags = NF_CT_EXPECT_PERMANENT; /* Accept multiple calls */

nathook = rcu_dereference(nfct_h323_nat_hook);
@@ -1305,7 +1305,7 @@ static int process_gcf(struct sk_buff *skb, struct nf_conn *ct,
nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, nf_ct_l3num(ct),
&ct->tuplehash[!dir].tuple.src.u3, &addr,
IPPROTO_UDP, NULL, &port);
- exp->helper = nf_conntrack_helper_ras;
+ rcu_assign_pointer(exp->helper, nf_conntrack_helper_ras);

if (nf_ct_expect_related(exp, 0) == 0) {
pr_debug("nf_ct_ras: expect RAS ");
@@ -1522,7 +1522,7 @@ static int process_acf(struct sk_buff *skb, struct nf_conn *ct,
&ct->tuplehash[!dir].tuple.src.u3, &addr,
IPPROTO_TCP, NULL, &port);
exp->flags = NF_CT_EXPECT_PERMANENT;
- exp->helper = nf_conntrack_helper_q931;
+ rcu_assign_pointer(exp->helper, nf_conntrack_helper_q931);

if (nf_ct_expect_related(exp, 0) == 0) {
pr_debug("nf_ct_ras: expect Q.931 ");
@@ -1576,7 +1576,7 @@ static int process_lcf(struct sk_buff *skb, struct nf_conn *ct,
&ct->tuplehash[!dir].tuple.src.u3, &addr,
IPPROTO_TCP, NULL, &port);
exp->flags = NF_CT_EXPECT_PERMANENT;
- exp->helper = nf_conntrack_helper_q931;
+ rcu_assign_pointer(exp->helper, nf_conntrack_helper_q931);

if (nf_ct_expect_related(exp, 0) == 0) {
pr_debug("nf_ct_ras: expect Q.931 ");
diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
index 9d7d36ac83083..a21c976701f79 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -399,7 +399,7 @@ static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
const struct nf_conntrack_helper *me = data;
const struct nf_conntrack_helper *this;

- if (exp->helper == me)
+ if (rcu_access_pointer(exp->helper) == me)
return true;

this = rcu_dereference_protected(help->helper,
@@ -421,6 +421,11 @@ void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)

nf_ct_expect_iterate_destroy(expect_iter_me, me);
nf_ct_iterate_destroy(unhelp, me);
+
+ /* nf_ct_iterate_destroy() does an unconditional synchronize_rcu() as
+ * last step, this ensures rcu readers of exp->helper are done.
+ * No need for another synchronize_rcu() here.
+ */
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 3b5da5e7e9d27..b67ab92d65bab 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -3566,7 +3566,7 @@ ctnetlink_alloc_expect(const struct nlattr * const cda[], struct nf_conn *ct,

exp->class = class;
exp->master = ct;
- 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;
diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index 17af0ff4ea7ab..5bddee342e122 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -1303,7 +1303,7 @@ static int process_register_request(struct sk_buff *skb, unsigned int protoff,
nf_ct_expect_init(exp, SIP_EXPECT_SIGNALLING, nf_ct_l3num(ct),
saddr, &daddr, proto, NULL, &port);
exp->timeout.expires = sip_timeout * HZ;
- exp->helper = helper;
+ rcu_assign_pointer(exp->helper, helper);
exp->flags = NF_CT_EXPECT_PERMANENT | NF_CT_EXPECT_INACTIVE;

hooks = rcu_dereference(nf_nat_sip_hooks);
--
2.53.0