netfilter: conntrack: fix possible bug_on with enable_hooks=1

I received a bug report (no reproducer so far) where we trip over 712 rcu_read_lock(); 713 ct_hook = rcu_dereference(nf_ct_hook); 714 BUG_ON(ct_hook == NULL); // here In nf_conntrack_destroy(). First turn this BUG_ON into a WARN. I think it was triggered via enable_hooks=1 flag. When this flag is turned on, the conntrack hooks are registered before nf_ct_hook pointer gets assigned. This opens a short window where packets enter the conntrack machinery, can have skb->_nfct set up and a subsequent kfree_skb might occur before nf_ct_hook is set. Call nf_conntrack_init_end() to set nf_ct_hook before we register the pernet ops. Fixes: ba3fbe6 ("netfilter: nf_conntrack: provide modparam to always register conntrack hooks") Signed-off-by: Florian Westphal <[email protected]> Signed-off-by: Pablo Neira Ayuso <[email protected]>
kawasaki · May 10, 2023 · e72eeab · e72eeab
1 parent dc1c9fd
commit e72eeab
Show file tree

Hide file tree

Showing 2 changed files with 6 additions and 3 deletions.
diff --git a/net/netfilter/core.c b/net/netfilter/core.c
@@ -711,9 +711,11 @@ void nf_conntrack_destroy(struct nf_conntrack *nfct)
 
 	rcu_read_lock();
 	ct_hook = rcu_dereference(nf_ct_hook);
-	BUG_ON(ct_hook == NULL);
-	ct_hook->destroy(nfct);
+	if (ct_hook)
+		ct_hook->destroy(nfct);
 	rcu_read_unlock();
+
+	WARN_ON(!ct_hook);
 }
 EXPORT_SYMBOL(nf_conntrack_destroy);
 

diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
@@ -1218,11 +1218,12 @@ static int __init nf_conntrack_standalone_init(void)
 	nf_conntrack_htable_size_user = nf_conntrack_htable_size;
 #endif
 
+	nf_conntrack_init_end();
+
 	ret = register_pernet_subsys(&nf_conntrack_net_ops);
 	if (ret < 0)
 		goto out_pernet;
 
-	nf_conntrack_init_end();
 	return 0;
 
 out_pernet: