[PATCH 5.15 011/203] netfilter: conntrack: fix possible bug_on with enable_hooks=1

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From: Florian Westphal <fw@xxxxxxxxx>

[ Upstream commit e72eeab542dbf4f544e389e64fa13b82a1b6d003 ]

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: ba3fbe663635 ("netfilter: nf_conntrack: provide modparam to always register conntrack hooks")
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/netfilter/core.c                    | 6 ++++--
 net/netfilter/nf_conntrack_standalone.c | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index cca0762a90102..8eed6536e7e7b 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -675,9 +675,11 @@ 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
index 338f02a12076b..7515705583bcf 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -1229,11 +1229,12 @@ 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:
-- 
2.39.2






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