netdev - [PATCH net-next 3/7] netfilter: Switch to skb_dst_reset to clear dst

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Message-ID: <20250812155245.507012-4-sdf@fomichev.me>
Date: Tue, 12 Aug 2025 08:52:41 -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 3/7] netfilter: Switch to skb_dst_reset to clear dst_entry

Going forward skb_dst_set will assert that skb dst_entry
is empty during skb_dst_set. skb_dst_reset is added to reset
existing entry without doing refcnt. Switch to skb_dst_reset
in ip[6]_route_me_harder and add a comment on why it's safe
to skip skb_dst_restore.

Signed-off-by: Stanislav Fomichev <sdf@...ichev.me>
---
 net/ipv4/netfilter.c | 5 ++++-
 net/ipv6/netfilter.c | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/netfilter.c b/net/ipv4/netfilter.c
index 0565f001120d..bda67bb0e63b 100644
--- a/net/ipv4/netfilter.c
+++ b/net/ipv4/netfilter.c
@@ -65,7 +65,10 @@ int ip_route_me_harder(struct net *net, struct sock *sk, struct sk_buff *skb, un
 	if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
 	    xfrm_decode_session(net, skb, flowi4_to_flowi(&fl4), AF_INET) == 0) {
 		struct dst_entry *dst = skb_dst(skb);
-		skb_dst_set(skb, NULL);
+		/* ignore return value from skb_dst_reset, xfrm_lookup takes
+		 * care of dropping the refcnt if needed.
+		 */
+		skb_dst_reset(skb);
 		dst = xfrm_lookup(net, dst, flowi4_to_flowi(&fl4), sk, 0);
 		if (IS_ERR(dst))
 			return PTR_ERR(dst);
diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index 45f9105f9ac1..6743c075133d 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -63,7 +63,10 @@ int ip6_route_me_harder(struct net *net, struct sock *sk_partial, struct sk_buff
 #ifdef CONFIG_XFRM
 	if (!(IP6CB(skb)->flags & IP6SKB_XFRM_TRANSFORMED) &&
 	    xfrm_decode_session(net, skb, flowi6_to_flowi(&fl6), AF_INET6) == 0) {
-		skb_dst_set(skb, NULL);
+		/* ignore return value from skb_dst_reset, xfrm_lookup takes
+		 * care of dropping the refcnt if needed.
+		 */
+		skb_dst_reset(skb);
 		dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), sk, 0);
 		if (IS_ERR(dst))
 			return PTR_ERR(dst);
-- 
2.50.1