[PATCH net-next v1 3/3] inet: Avoid ehash lookup race in inet_twsk_hashdance_schedule()
From: <hidden>
Date: 2025-09-15 07:04:44
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
From: Xuanqiang Luo <redacted>
Since ehash lookups are lockless, if another CPU is converting sk to tw
concurrently, fetching the newly inserted tw with tw->tw_refcnt == 0 cause
lookup failure.
The call trace map is drawn as follows:
CPU 0 CPU 1
----- -----
inet_twsk_hashdance_schedule()
spin_lock()
inet_twsk_add_node_rcu(tw, ...)
__inet_lookup_established()
(find tw, failure due to tw_refcnt = 0)
__sk_nulls_del_node_init_rcu(sk)
refcount_set(&tw->tw_refcnt, 3)
spin_unlock()
By replacing sk with tw atomically via hlist_nulls_replace_init_rcu() after
setting tw_refcnt, we ensure that tw is either fully initialized or not
visible to other CPUs, eliminating the race.
Fixes: 3ab5aee7fe84 ("net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls")
Signed-off-by: Xuanqiang Luo <redacted>
---
net/ipv4/inet_timewait_sock.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 5b5426b8ee92..4c84a020315d 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c@@ -115,8 +115,9 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash); spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash); struct inet_bind_hashbucket *bhead, *bhead2; + bool ret = false; - /* Step 1: Put TW into bind hash. Original socket stays there too. + /* Put TW into bind hash. Original socket stays there too. Note, that any socket with inet->num != 0 MUST be bound in binding cache, even if it is closed. */
@@ -140,14 +141,6 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, spin_lock(lock); - /* Step 2: Hash TW into tcp ehash chain */ - inet_twsk_add_node_rcu(tw, &ehead->chain); - - /* Step 3: Remove SK from hash chain */ - if (__sk_nulls_del_node_init_rcu(sk)) - sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); - - /* Ensure above writes are committed into memory before updating the * refcount. * Provides ordering vs later refcount_inc().
@@ -162,6 +155,15 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, */ refcount_set(&tw->tw_refcnt, 3); + if (sk_hashed(sk)) { + ret = hlist_nulls_replace_init_rcu(&sk->sk_nulls_node, + &tw->tw_node); + sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); + } + + if (!ret) + inet_twsk_add_node_rcu(tw, &ehead->chain); + inet_twsk_schedule(tw, timeo); spin_unlock(lock);
--
2.27.0