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>
This commit is contained in:
Liping Zhang 2017-03-25 08:53:12 +08:00 committed by Pablo Neira Ayuso
parent f83bf8da11
commit 3b7dabf029
5 changed files with 7 additions and 1 deletions

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@ -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);
}

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@ -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);

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@ -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);

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@ -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]);

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@ -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);