linux-kernel - [PATCH net-next] net: ip: lookup the best matched listen socket

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Message-ID: <20250731123309.184496-1-dongml2@chinatelecom.cn>
Date: Thu, 31 Jul 2025 20:33:09 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: edumazet@...gle.com
Cc: ncardwell@...gle.com,
	kuniyu@...gle.com,
	davem@...emloft.net,
	dsahern@...nel.org,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net-next] net: ip: lookup the best matched listen socket

For now, the socket lookup will terminate if the socket is reuse port in
inet_lhash2_lookup(), which makes the socket is not the best match.

For example, we have socket1 and socket2 both listen on "0.0.0.0:1234",
but socket1 bind on "eth0". We create socket1 first, and then socket2.
Then, all connections will goto socket2, which is not expected, as socket1
has higher priority.

This can cause unexpected behavior if TCP MD5 keys is used, as described
in Documentation/networking/vrf.rst -> Applications.

Therefor, we lookup the best matched socket first, and then do the reuse
port logic. This can increase some overhead if there are many reuse port
socket :/

Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
 net/ipv4/inet_hashtables.c  | 13 +++++++------
 net/ipv6/inet6_hashtables.c | 13 +++++++------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index ceeeec9b7290..51751337f394 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -389,17 +389,18 @@ static struct sock *inet_lhash2_lookup(const struct net *net,
 	sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
 		score = compute_score(sk, net, hnum, daddr, dif, sdif);
 		if (score > hiscore) {
-			result = inet_lookup_reuseport(net, sk, skb, doff,
-						       saddr, sport, daddr, hnum, inet_ehashfn);
-			if (result)
-				return result;
-
 			result = sk;
 			hiscore = score;
 		}
 	}
 
-	return result;
+	if (!result)
+		return NULL;
+
+	sk = inet_lookup_reuseport(net, result, skb, doff,
+				   saddr, sport, daddr, hnum, inet_ehashfn);
+
+	return sk ? sk : result;
 }
 
 struct sock *inet_lookup_run_sk_lookup(const struct net *net,
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index 76ee521189eb..2554f26d6c20 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -161,17 +161,18 @@ static struct sock *inet6_lhash2_lookup(const struct net *net,
 	sk_nulls_for_each_rcu(sk, node, &ilb2->nulls_head) {
 		score = compute_score(sk, net, hnum, daddr, dif, sdif);
 		if (score > hiscore) {
-			result = inet6_lookup_reuseport(net, sk, skb, doff,
-							saddr, sport, daddr, hnum, inet6_ehashfn);
-			if (result)
-				return result;
-
 			result = sk;
 			hiscore = score;
 		}
 	}
 
-	return result;
+	if (!result)
+		return NULL;
+
+	sk = inet6_lookup_reuseport(net, result, skb, doff,
+				    saddr, sport, daddr, hnum, inet6_ehashfn);
+
+	return sk ? sk : result;
 }
 
 struct sock *inet6_lookup_run_sk_lookup(const struct net *net,
-- 
2.50.1