[PATCH nf-next,v2] netfilter: add DEBUG_NET_WARN_ON_ONCE to skb_set_nfct()

Trigger a warning if nf_ct_set() overlaps an existing ct object leading
to refcount leak. Add this warning to skb_set_nfct() whose only user is
nf_ct_set() instead.

Update existing nf_ct_set() callers to use nf_reset_ct() first to clean
up stale pointer to conntrack object which migh trigger false positive
warnings.

Signed-off-by: Pablo Neira Ayuso <[email protected]>
---
sashiko: ignore current overwrites of skb->_nfct in
net/bridge/netfilter/nf_conntrack_bridge.c:nf_ct_bridge_pre(),
that will be fixed in a separated patch.

 include/linux/skbuff.h            |  1 +
 include/net/ip_vs.h               |  2 +-
 net/netfilter/nf_conntrack_core.c |  2 +-
 net/openvswitch/conntrack.c       | 12 +++---------
 net/sched/act_ct.c                |  6 +++---
 5 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 22eda1d54a0e..95184183180f 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -5004,6 +5004,7 @@ static inline unsigned long skb_get_nfct(const struct sk_buff *skb)
 static inline void skb_set_nfct(struct sk_buff *skb, unsigned long nfct)
 {
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
+	DEBUG_NET_WARN_ON_ONCE(skb->_nfct & NFCT_PTRMASK);
 	skb->slow_gro |= !!nfct;
 	skb->_nfct = nfct;
 #endif
diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index 8feb69158816..9c6c5336de1c 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -2130,7 +2130,7 @@ static inline void ip_vs_notrack(struct sk_buff *skb)
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 
 	if (ct) {
-		nf_conntrack_put(&ct->ct_general);
+		nf_reset_ct(skb);
 		nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
 	}
 #endif
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 784bd1d7a9bf..d0d9e5ea84a0 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1031,7 +1031,7 @@ static int __nf_ct_resolve_clash(struct sk_buff *skb,
 		nf_conntrack_get(&ct->ct_general);
 
 		nf_ct_acct_merge(ct, ctinfo, loser_ct);
-		nf_ct_put(loser_ct);
+		nf_reset_ct(skb);
 		nf_ct_set(skb, ct, ctinfo);
 
 		NF_CT_STAT_INC(net, clash_resolve);
diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
index 95697d4e16e6..4dd82c4e87d3 100644
--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -603,7 +603,7 @@ static bool skb_nfct_cached(struct net *net,
 		if (nf_ct_is_confirmed(ct))
 			nf_ct_delete(ct, 0, 0);
 
-		nf_ct_put(ct);
+		nf_reset_ct(skb);
 		nf_ct_set(skb, NULL, 0);
 		return false;
 	}
@@ -745,8 +745,7 @@ static int __ovs_ct_lookup(struct net *net, struct sw_flow_key *key,
 
 		/* Associate skb with specified zone. */
 		if (tmpl) {
-			ct = nf_ct_get(skb, &ctinfo);
-			nf_ct_put(ct);
+			nf_reset_ct(skb);
 			nf_conntrack_get(&tmpl->ct_general);
 			nf_ct_set(skb, tmpl, IP_CT_NEW);
 		}
@@ -1075,12 +1074,7 @@ int ovs_ct_execute(struct net *net, struct sk_buff *skb,
 
 int ovs_ct_clear(struct sk_buff *skb, struct sw_flow_key *key)
 {
-	enum ip_conntrack_info ctinfo;
-	struct nf_conn *ct;
-
-	ct = nf_ct_get(skb, &ctinfo);
-
-	nf_ct_put(ct);
+	nf_reset_ct(skb);
 	nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
 
 	if (key)
diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
index 4ca7964e83c8..7f54fb4e4ec9 100644
--- a/net/sched/act_ct.c
+++ b/net/sched/act_ct.c
@@ -782,7 +782,7 @@ static bool tcf_ct_skb_nfct_cached(struct net *net, struct sk_buff *skb,
 	return true;
 
 drop_ct:
-	nf_ct_put(ct);
+	nf_reset_ct(skb);
 	nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
 
 	return false;
@@ -996,7 +996,7 @@ TC_INDIRECT_SCOPE int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
 		qdisc_skb_cb(skb)->post_ct = false;
 		ct = nf_ct_get(skb, &ctinfo);
 		if (ct) {
-			nf_ct_put(ct);
+			nf_reset_ct(skb);
 			nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
 		}
 
@@ -1034,7 +1034,7 @@ TC_INDIRECT_SCOPE int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
 
 		/* Associate skb with specified zone. */
 		if (tmpl) {
-			nf_conntrack_put(skb_nfct(skb));
+			nf_reset_ct(skb);
 			nf_conntrack_get(&tmpl->ct_general);
 			nf_ct_set(skb, tmpl, IP_CT_NEW);
 		}
-- 
2.47.3