[PATCH net 4/9] netfilter: synproxy: add mutex to guard hook reference counting

[Pablo Neira Ayuso <pablo@netfilter.org>]

From: Fernando Fernandez Mancera <fmancera@suse.de>

As the synproxy infrastructure register netfilter hooks on-demand when a
user adds the first iptables target or nftables expression, if done
concurrently they can race each other.

Introduce a mutex to serialize the refcount control blocks access from
both frontends. While a per namespace mutex might be more efficient, it
is not needed for target/expression like SYNPROXY.

Fixes: ad49d86e07a4 ("netfilter: nf_tables: Add synproxy support")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nf_synproxy_core.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index 036c8586f49b..ed00114f65f3 100644
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -22,6 +22,8 @@
 #include <net/netfilter/nf_conntrack_zones.h>
 #include <net/netfilter/nf_synproxy.h>
 
+static DEFINE_MUTEX(synproxy_mutex);
+
 unsigned int synproxy_net_id;
 EXPORT_SYMBOL_GPL(synproxy_net_id);
 
@@ -769,26 +771,31 @@ static const struct nf_hook_ops ipv4_synproxy_ops[] = {
 
 int nf_synproxy_ipv4_init(struct synproxy_net *snet, struct net *net)
 {
-	int err;
+	int err = 0;
 
+	mutex_lock(&synproxy_mutex);
 	if (snet->hook_ref4 == 0) {
 		err = nf_register_net_hooks(net, ipv4_synproxy_ops,
 					    ARRAY_SIZE(ipv4_synproxy_ops));
 		if (err)
-			return err;
+			goto out;
 	}
 
 	snet->hook_ref4++;
-	return 0;
+out:
+	mutex_unlock(&synproxy_mutex);
+	return err;
 }
 EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_init);
 
 void nf_synproxy_ipv4_fini(struct synproxy_net *snet, struct net *net)
 {
+	mutex_lock(&synproxy_mutex);
 	snet->hook_ref4--;
 	if (snet->hook_ref4 == 0)
 		nf_unregister_net_hooks(net, ipv4_synproxy_ops,
 					ARRAY_SIZE(ipv4_synproxy_ops));
+	mutex_unlock(&synproxy_mutex);
 }
 EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_fini);
 
@@ -1193,27 +1200,32 @@ static const struct nf_hook_ops ipv6_synproxy_ops[] = {
 int
 nf_synproxy_ipv6_init(struct synproxy_net *snet, struct net *net)
 {
-	int err;
+	int err = 0;
 
+	mutex_lock(&synproxy_mutex);
 	if (snet->hook_ref6 == 0) {
 		err = nf_register_net_hooks(net, ipv6_synproxy_ops,
 					    ARRAY_SIZE(ipv6_synproxy_ops));
 		if (err)
-			return err;
+			goto out;
 	}
 
 	snet->hook_ref6++;
-	return 0;
+out:
+	mutex_unlock(&synproxy_mutex);
+	return err;
 }
 EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_init);
 
 void
 nf_synproxy_ipv6_fini(struct synproxy_net *snet, struct net *net)
 {
+	mutex_lock(&synproxy_mutex);
 	snet->hook_ref6--;
 	if (snet->hook_ref6 == 0)
 		nf_unregister_net_hooks(net, ipv6_synproxy_ops,
 					ARRAY_SIZE(ipv6_synproxy_ops));
+	mutex_unlock(&synproxy_mutex);
 }
 EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_fini);
 #endif /* CONFIG_IPV6 */
-- 
2.47.3