From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (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 B50BE1FCFEF for ; Fri, 26 Sep 2025 03:25:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758857125; cv=none; b=SEbCaKlu9vb9U1fJOVeaDvEGM0wQO28D/+jkBYmc4BoA0Ad9QcO17FT8pdORrqOOduigUJqjP5R0fWTPYMtsobCGKR0sAeFegyxxk7BtTx0oV6RRbff+riMuIjpaJWY+GJH/x/gil74en2EyCdHwrDVJR7Q+vHTS4BG2rNu7n7s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758857125; c=relaxed/simple; bh=b/9pJO8xCL8+gZ7x0NMAA6lnkmvXZc/T4bwyWivKvhY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VB3IUP3pN79vj9aIdF+cmjB7+ijbu9zceb0MZllpmBIwJREe9bs0QHn6xJSbTe18NH5fQT/Zvl0X5EOdkgoZ4MwbI86LW21segniX24rlN+Tvlo6C91F2LrBf4U0px3M+YsMRowzKYhG6+y93y0V5hORmPtm/GoK2m34DsIsLIU= 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=jnpt4DWP; arc=none smtp.client-ip=95.215.58.182 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="jnpt4DWP" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758857118; 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=ZC6ZIAFSlhuyGbA65PUFrc6pN/4Sah8QwAuSxpB+7vI=; b=jnpt4DWPaGP+wnBV+DSZ/343wYhxus0AaQC/5rLPDReQ1mTynCp926lxRtMGn4ldMJZWZV Dq3mLJEMfATvf93RmaZ14Lv8vlL/E+1j2eurf2Y5XyTs4yWDOynl26FXxutpA7m4vobjh1 dgQ5E9Ekm3b/qvGlW+DdRWaOc3gWsB0= Date: Fri, 26 Sep 2025 11:25:15 +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 v6 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: <20250925021628.886203-1-xuanqiang.luo@linux.dev> <20250925021628.886203-4-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 2025/9/26 02:22, Kuniyuki Iwashima 写道: > On Wed, Sep 24, 2025 at 7:18 PM 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. >> >> 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 | 31 ++++++++++--------------------- >> 1 file changed, 10 insertions(+), 21 deletions(-) >> >> diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c >> index 5b5426b8ee92..89dc0a5d7248 100644 >> --- a/net/ipv4/inet_timewait_sock.c >> +++ b/net/ipv4/inet_timewait_sock.c >> @@ -87,12 +87,6 @@ void inet_twsk_put(struct inet_timewait_sock *tw) >> } >> EXPORT_SYMBOL_GPL(inet_twsk_put); >> >> -static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw, >> - struct hlist_nulls_head *list) >> -{ >> - hlist_nulls_add_head_rcu(&tw->tw_node, list); >> -} >> - >> static void inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo) >> { >> __inet_twsk_schedule(tw, timeo, false); >> @@ -112,11 +106,10 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, >> { >> const struct inet_sock *inet = inet_sk(sk); >> const struct inet_connection_sock *icsk = inet_csk(sk); >> - 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; >> >> - /* 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. > While at it, could you update the comment style at these 2 line above too ? > > /* Put .. > * Note, ... > * binding ... > */ > > Otherwise looks good, thanks. > > Reviewed-by: Kuniyuki Iwashima > I'll fix the comment style in the next version. Thanks for the review! > > >> */ >> @@ -140,19 +133,6 @@ 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 +142,15 @@ 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 >>