netfilter: invoke synchronize_rcu after set the _hook_ to NULL

Otherwise, another CPU may access the invalid pointer. For example:
    CPU0                CPU1
     -              rcu_read_lock();
     -              pfunc = _hook_;
  _hook_ = NULL;          -
  mod unload              -
     -                 pfunc(); // invalid, panic
     -             rcu_read_unlock();

So we must call synchronize_rcu() to wait the rcu reader to finish.

Also note, in nf_nat_snmp_basic_fini, synchronize_rcu() will be invoked
by later nf_conntrack_helper_unregister, but I'm inclined to add a
explicit synchronize_rcu after set the nf_nat_snmp_hook to NULL. Depend
on such obscure assumptions is not a good idea.

Last, in nfnetlink_cttimeout, we use kfree_rcu to free the time object,
so in cttimeout_exit, invoking rcu_barrier() is not necessary at all,
remove it too.

Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/ipv4/netfilter/nf_nat_snmp_basic.c b/net/ipv4/netfilter/nf_nat_snmp_basic.c
index c9b52c3..5a8f7c3 100644 (file)
--- a/net/ipv4/netfilter/nf_nat_snmp_basic.c
+++ b/net/ipv4/netfilter/nf_nat_snmp_basic.c
@@ -1304,6 +1304,7 @@ static int __init nf_nat_snmp_basic_init(void)
 static void __exit nf_nat_snmp_basic_fini(void)
 {
        RCU_INIT_POINTER(nf_nat_snmp_hook, NULL);
+       synchronize_rcu();
        nf_conntrack_helper_unregister(&snmp_trap_helper);
 }
 

diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c
index da9df2d..22fc321 100644 (file)
--- a/net/netfilter/nf_conntrack_ecache.c
+++ b/net/netfilter/nf_conntrack_ecache.c
@@ -290,6 +290,7 @@ void nf_conntrack_unregister_notifier(struct net *net,
        BUG_ON(notify != new);
        RCU_INIT_POINTER(net->ct.nf_conntrack_event_cb, NULL);
        mutex_unlock(&nf_ct_ecache_mutex);
+       /* synchronize_rcu() is called from ctnetlink_exit. */
 }
 EXPORT_SYMBOL_GPL(nf_conntrack_unregister_notifier);
 
@@ -326,6 +327,7 @@ void nf_ct_expect_unregister_notifier(struct net *net,
        BUG_ON(notify != new);
        RCU_INIT_POINTER(net->ct.nf_expect_event_cb, NULL);
        mutex_unlock(&nf_ct_ecache_mutex);
+       /* synchronize_rcu() is called from ctnetlink_exit. */
 }
 EXPORT_SYMBOL_GPL(nf_ct_expect_unregister_notifier);
 

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 6806b5e..908d858 100644 (file)
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -3442,6 +3442,7 @@ static void __exit ctnetlink_exit(void)
 #ifdef CONFIG_NETFILTER_NETLINK_GLUE_CT
        RCU_INIT_POINTER(nfnl_ct_hook, NULL);
 #endif
+       synchronize_rcu();
 }
 
 module_init(ctnetlink_init);

diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index 94b14c5..82802e4 100644 (file)
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -903,6 +903,8 @@ static void __exit nf_nat_cleanup(void)
 #ifdef CONFIG_XFRM
        RCU_INIT_POINTER(nf_nat_decode_session_hook, NULL);
 #endif
+       synchronize_rcu();
+
        for (i = 0; i < NFPROTO_NUMPROTO; i++)
                kfree(nf_nat_l4protos[i]);
 

diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
index 139e086..47d6656 100644 (file)
--- a/net/netfilter/nfnetlink_cttimeout.c
+++ b/net/netfilter/nfnetlink_cttimeout.c
@@ -646,8 +646,8 @@ static void __exit cttimeout_exit(void)
 #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
        RCU_INIT_POINTER(nf_ct_timeout_find_get_hook, NULL);
        RCU_INIT_POINTER(nf_ct_timeout_put_hook, NULL);
+       synchronize_rcu();
 #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
-       rcu_barrier();
 }
 
 module_init(cttimeout_init);