[PATCH net 2/2] net: Warn when overriding referenced dst entry

[Stanislav Fomichev <sdf@fomichev.me>]

Add WARN_ON_ONCE with CONFIG_NET_DEBUG to warn on overriding referenced
dst entries. This should get a better signal than tracing leaked
objects from kmemleak.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
---
 include/linux/skbuff.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 5520524c93bf..c89931ac01e5 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1159,6 +1159,12 @@ static inline struct dst_entry *skb_dst(const struct sk_buff *skb)
 	return (struct dst_entry *)(skb->_skb_refdst & SKB_DST_PTRMASK);
 }
 
+static inline void skb_dst_check(struct sk_buff *skb)
+{
+	DEBUG_NET_WARN_ON_ONCE(skb_dst(skb) &&
+			       !(skb->_skb_refdst & SKB_DST_NOREF));
+}
+
 /**
  * skb_dst_set - sets skb dst
  * @skb: buffer
@@ -1169,6 +1175,7 @@ static inline struct dst_entry *skb_dst(const struct sk_buff *skb)
  */
 static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
 {
+	skb_dst_check(skb);
 	skb->slow_gro |= !!dst;
 	skb->_skb_refdst = (unsigned long)dst;
 }
@@ -1185,6 +1192,7 @@ static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
  */
 static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
 {
+	skb_dst_check(skb);
 	WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
 	skb->slow_gro |= !!dst;
 	skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
-- 
2.50.1