netfilter: Switch to skb_dstref_steal to clear dst_entry

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

Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250818154032.3173645-4-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/netfilter.c b/net/ipv4/netfilter.c
index 0565f001120dcae8a7f6a552c40bb897b4786abb..e60e54e7945d2254bf12f73fd9a5a84fdb7b1ec8 100644 (file)
--- 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_dstref_steal, xfrm_lookup takes
+                * care of dropping the refcnt if needed.
+                */
+               skb_dstref_steal(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 45f9105f9ac1e1497c6471b01ce515d4d8672eed..46540a5a43317a418c29cf649099006464f3809f 100644 (file)
--- 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_dstref_steal, xfrm_lookup takes
+                * care of dropping the refcnt if needed.
+                */
+               skb_dstref_steal(skb);
                dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), sk, 0);
                if (IS_ERR(dst))
                        return PTR_ERR(dst);