netdev - [PATCH net-next 7/7] net: Add skb_dst_check

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Message-ID: <20250812155245.507012-8-sdf@fomichev.me>
Date: Tue, 12 Aug 2025 08:52:45 -0700
From: Stanislav Fomichev <sdf@...ichev.me>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	ayush.sawal@...lsio.com,
	andrew+netdev@...n.ch,
	gregkh@...uxfoundation.org,
	horms@...nel.org,
	dsahern@...nel.org,
	pablo@...filter.org,
	kadlec@...filter.org,
	steffen.klassert@...unet.com,
	sdf@...ichev.me,
	mhal@...x.co,
	abhishektamboli9@...il.com,
	linux-kernel@...r.kernel.org,
	linux-staging@...ts.linux.dev,
	netfilter-devel@...r.kernel.org,
	coreteam@...filter.org,
	herbert@...dor.apana.org.au
Subject: [PATCH net-next 7/7] net: Add skb_dst_check_unset

To prevent dst_entry leaks, add warning when the non-NULL dst_entry
is rewritten.

Signed-off-by: Stanislav Fomichev <sdf@...ichev.me>
---
 include/linux/skbuff.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8240e0826204..2f9dac54d627 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_unset(struct sk_buff *skb)
+{
+	DEBUG_NET_WARN_ON_ONCE((skb->_skb_refdst & SKB_DST_PTRMASK) &&
+			       !(skb->_skb_refdst & SKB_DST_NOREF));
+}
+
 /**
  * skb_dst_reset() - return current dst_entry value and clear it
  * @skb: buffer
@@ -1187,6 +1193,7 @@ static inline unsigned long skb_dst_reset(struct sk_buff *skb)
  */
 static inline void skb_dst_restore(struct sk_buff *skb, unsigned long refdst)
 {
+	skb_dst_check_unset(skb);
 	skb->_skb_refdst = refdst;
 }
 
@@ -1200,6 +1207,7 @@ static inline void skb_dst_restore(struct sk_buff *skb, unsigned long refdst)
  */
 static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
 {
+	skb_dst_check_unset(skb);
 	skb->slow_gro |= !!dst;
 	skb->_skb_refdst = (unsigned long)dst;
 }
@@ -1216,6 +1224,7 @@ 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_unset(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