From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (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 9E60421D596 for ; Wed, 17 Sep 2025 03:27:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758079661; cv=none; b=hYs7sbBL/GAvPh8n03yLv8hsIiMdo1cn/aDCrjrmQR3Ieya7y1RjZZAXgSUQmHncuu6cps17cgU5zv0nRos0ESHaMYQ1z8X5JjgCC4RgJFRS01Ffivsp2Neay5RlCWwdMpDmuyxPdvHln2ORxWiUy7L9RUoadB2Mlv6Feer1dLA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758079661; c=relaxed/simple; bh=/exDfsXAQYImhf1ve1EB+Oyy/zzI2sbKBm7luABqx9A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dHGJUdzFcqlrpP869eT8ysAvmYwxv4nqR4rUb7E6WaWVdKeLhzOufSIT2iQMdxMUiorMbuSFVhKMRiAY5CHgcg5q57Sk4c33tQS/HwpX4iOpSltJcS5xYeCWaXK1OmFhP6JkNqRow8AUVP+51ARwKeGzyBXpyzO7dY7sUG/2M9s= 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=wFHVRQJU; arc=none smtp.client-ip=91.218.175.181 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="wFHVRQJU" Message-ID: <9d6b887f-c75c-468b-beaf-a3c7979bd132@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758079657; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7681q6EAVxjrEtOyM6YnBHuXGfO0p05G/R5mEeqe4oY=; b=wFHVRQJUOnpxeu01FuE9KnzOBkUcBfQ9llut9k2wxh9217Tv+AuEcqs7tM4uu8Fx+Uhsez Mk5pYBqoeqNBt3MttylzPpWeIhAv7tkR8eprqUD3DD/XAY/deWz4dYdVQHwWkPH77y53Ek sEl+6sm4VwiTuWD1K5pieqMfl5CBgP0= Date: Wed, 17 Sep 2025 11:26:57 +0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH net-next v3 3/3] inet: Avoid ehash lookup race in inet_twsk_hashdance_schedule() To: Kuniyuki Iwashima Cc: edumazet@google.com, kerneljasonxing@gmail.com, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, Xuanqiang Luo References: <20250916103054.719584-1-xuanqiang.luo@linux.dev> <20250916103054.719584-4-xuanqiang.luo@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: luoxuanqiang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2025/9/17 03:48, Kuniyuki Iwashima 写道: > On Tue, Sep 16, 2025 at 3:31 AM wrote: >> 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. >> >> Fixes: 3ab5aee7fe84 ("net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls") >> Signed-off-by: Xuanqiang Luo >> --- >> net/ipv4/inet_timewait_sock.c | 15 ++++++--------- >> 1 file changed, 6 insertions(+), 9 deletions(-) >> >> diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c >> index 5b5426b8ee92..1ba20c4cb73b 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. >> */ >> @@ -140,14 +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(). >> @@ -162,6 +154,11 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, >> */ >> refcount_set(&tw->tw_refcnt, 3); >> >> + if (hlist_nulls_replace_init_rcu(&sk->sk_nulls_node, &tw->tw_node)) >> + sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); >> + else >> + inet_twsk_add_node_rcu(tw, &ehead->chain); > When hlist_nulls_replace_init_rcu() returns false ? When hlist_nulls_replace_init_rcu() returns false, it means sk is unhashed, the replacement operation failed, we need to insert tw, and this doesn't change the original logic. > >> + >> inet_twsk_schedule(tw, timeo); >> >> spin_unlock(lock); >> -- >> 2.25.1 >>