From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 78FCF1F4613 for ; Wed, 24 Sep 2025 01:52:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758678729; cv=none; b=SO9Qn193s8/2unc86nmLWoNoBs7EDehVohvYozumgU92znTDlDZRDGJ2aJJUPMUYeSIZU/P3hA/0YAef+pR4JhT6rwxCSzPveJxLBoO4D6ZY9le5cKdYzA9pZmZ+IQ7sdeoqwvXWotiQtGGTT27l9jWIPcbpafJsa7kkcq6QoJA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758678729; c=relaxed/simple; bh=e7euEuyuUOWkQs+G24dHpqmwtNP6bZvxotjCQwX24dE=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=isMj6XcMtIEvcNY+WsNaARL6nHWGj0bIhlo3aN7weIUqfWjXtgXCMLm+n2gWytpkAswYqGxj93+Rhk4Lfbni0uhUzF7cwlhqt63YxW5ZMjLwx/gBiFXIdmelfQ7dA3lWZgjpwMy+LVOpn8Di09edrq5UaICc7ZOM8vLYA/EM4mA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=jw2pSHnp; arc=none smtp.client-ip=95.215.58.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="jw2pSHnp" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758678724; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gS+OD+4HXFus07t93li+HrvjfotaqDDoeyNQ/sjFJR8=; b=jw2pSHnpJkEdpxHsqfrPwUC9qARRypeiL5VfeuW5YbwQik1pcWXybLMiD/TQ5NbpF1QBSa vwTtb79Ikp5fPyqjpXhZs9oEOMJk2rEehgMpBQuy5AkS1AlZhm9SDE4T3qdb6WFi+9RuS/ V83etM+5Bb6abhlunRt73ZJEywheqjs= From: xuanqiang.luo@linux.dev To: edumazet@google.com, kuniyu@google.com Cc: kerneljasonxing@gmail.com, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, Xuanqiang Luo Subject: [PATCH net-next v5 3/3] inet: Avoid ehash lookup race in inet_twsk_hashdance_schedule() Date: Wed, 24 Sep 2025 09:50:34 +0800 Message-Id: <20250924015034.587056-4-xuanqiang.luo@linux.dev> In-Reply-To: <20250924015034.587056-1-xuanqiang.luo@linux.dev> References: <20250924015034.587056-1-xuanqiang.luo@linux.dev> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Xuanqiang Luo 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. It's worth noting that we held lock_sock() before the replacement, so there's no need to check if sk is hashed. Thanks to Kuniyuki Iwashima! Fixes: 3ab5aee7fe84 ("net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls") Signed-off-by: Xuanqiang Luo --- net/ipv4/inet_timewait_sock.c | 24 ++++++++++-------------- 1 file changed, 10 insertions(+), 14 deletions(-) diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c index 5b5426b8ee92..80b9ef3a128f 100644 --- a/net/ipv4/inet_timewait_sock.c +++ b/net/ipv4/inet_timewait_sock.c @@ -116,7 +116,7 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash); struct inet_bind_hashbucket *bhead, *bhead2; - /* 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. */ @@ -140,19 +140,6 @@ 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(). - */ - smp_wmb(); /* tw_refcnt is set to 3 because we have : * - one reference for bhash chain. * - one reference for ehash chain. @@ -162,6 +149,15 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, */ refcount_set(&tw->tw_refcnt, 3); + /* Ensure tw_refcnt has been set before tw is published. + * smp_wmb() provides the necessary memory barrier to enforce this + * ordering. + */ + smp_wmb(); + + hlist_nulls_replace_init_rcu(&sk->sk_nulls_node, &tw->tw_node); + sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); + inet_twsk_schedule(tw, timeo); spin_unlock(lock); -- 2.25.1