netfilter: nf_conntrack_expect: honor expectation helper field

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 <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>

Author: ummakynes

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;

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);

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;
 

net/netfilter/nf_conntrack_h323_main.c

@@ -643,7 +643,7 @@ 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,
@@ -767,7 +767,7 @@ 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,
@@ -1234,7 +1234,7 @@ 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);
@@ -1306,7 +1306,7 @@ 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 ");
@@ -1523,7 +1523,7 @@ 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 ");
@@ -1577,7 +1577,7 @@ 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 ");

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, NULL);
 	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);
 

net/netfilter/nf_conntrack_netlink.c

@@ -3573,7 +3573,7 @@ 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;

net/netfilter/nf_conntrack_sip.c

@@ -1297,7 +1297,7 @@ 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);