netdev - Re: [PATCH net-next v5 3/3] inet: Avoid ehash lookup race in inet_twsk_hashdance

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250924175527.4642e32a@kernel.org>
Date: Wed, 24 Sep 2025 17:55:27 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: xuanqiang.luo@...ux.dev
Cc: edumazet@...gle.com, kuniyu@...gle.com, kerneljasonxing@...il.com,
 davem@...emloft.net, netdev@...r.kernel.org, Xuanqiang Luo
 <luoxuanqiang@...inos.cn>
Subject: Re: [PATCH net-next v5 3/3] inet: Avoid ehash lookup race in
 inet_twsk_hashdance_schedule()

On Wed, 24 Sep 2025 09:50:34 +0800 xuanqiang.luo@...ux.dev wrote:
> From: Xuanqiang Luo <luoxuanqiang@...inos.cn>
> 
> 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.

This one doesn't build cleanly

net/ipv4/inet_timewait_sock.c:116:28: warning: unused variable 'ehead' [-Wunused-variable]
  116 |         struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
      |                                   ^~~~~
net/ipv4/inet_timewait_sock.c:91:13: warning: unused function 'inet_twsk_add_node_rcu' [-Wunused-function]
   91 | static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
      |             ^~~~~~~~~~~~~~~~~~~~~~
-- 
pw-bot: cr