linux-kernel - [PATCH v2] inet: fix fast path in __inet_hash

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Message-Id: <20230112-inet_hash_connect_bind_head-v2-1-5ec926ddd985@diag.uniroma1.it>
Date:   Fri, 13 Jan 2023 11:39:47 +0000
From:   Pietro Borrello <borrello@...g.uniroma1.it>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>
Cc:     Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jkl820.git@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Pietro Borrello <borrello@...g.uniroma1.it>
Subject: [PATCH v2] inet: fix fast path in __inet_hash_connect()

__inet_hash_connect() has a fast path taken if sk_head(&tb->owners) is
equal to the sk parameter.
sk_head() returns the hlist_entry() with respect to the sk_node field.
However entries in the tb->owners list are inserted with respect to the
sk_bind_node field with sk_add_bind_node().
Thus the check would never pass and the fast path never execute.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>
Signed-off-by: Pietro Borrello <borrello@...g.uniroma1.it>
---
Changes in v2:
- nit: s/list_entry/hlist_entry/
- Link to v1: https://lore.kernel.org/r/20230112-inet_hash_connect_bind_head-v1-1-7e3c770157c8@diag.uniroma1.it
---
 include/net/sock.h         | 10 ++++++++++
 net/ipv4/inet_hashtables.c |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index dcd72e6285b2..23fc403284db 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -860,6 +860,16 @@ static inline void sk_nulls_add_node_rcu(struct sock *sk, struct hlist_nulls_hea
 	__sk_nulls_add_node_rcu(sk, list);
 }
 
+static inline struct sock *__sk_bind_head(const struct hlist_head *head)
+{
+	return hlist_entry(head->first, struct sock, sk_bind_node);
+}
+
+static inline struct sock *sk_bind_head(const struct hlist_head *head)
+{
+	return hlist_empty(head) ? NULL : __sk_bind_head(head);
+}
+
 static inline void __sk_del_bind_node(struct sock *sk)
 {
 	__hlist_del(&sk->sk_bind_node);
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index d039b4e732a3..a805e086fb48 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -998,7 +998,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
 						  hinfo->bhash_size)];
 		tb = inet_csk(sk)->icsk_bind_hash;
 		spin_lock_bh(&head->lock);
-		if (sk_head(&tb->owners) == sk && !sk->sk_bind_node.next) {
+		if (sk_bind_head(&tb->owners) == sk && !sk->sk_bind_node.next) {
 			inet_ehash_nolisten(sk, NULL, NULL);
 			spin_unlock_bh(&head->lock);
 			return 0;

---
base-commit: 1b929c02afd37871d5afb9d498426f83432e71c2
change-id: 20230112-inet_hash_connect_bind_head-8f2dc98f08b1

Best regards,
-- 
Pietro Borrello <borrello@...g.uniroma1.it>