netdev - Re: [PATCH net-next v8 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: <CANn89iKjBJ_GUKk0+k5AHbhtp_cmN4e-PYU6j9_+XEVBspRUaA@mail.gmail.com>
Date: Wed, 15 Oct 2025 02:02:08 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: xuanqiang.luo@...ux.dev
Cc: kuniyu@...gle.com, pabeni@...hat.com, kerneljasonxing@...il.com, 
	davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org, 
	horms@...nel.org, jiayuan.chen@...ux.dev, ncardwell@...gle.com, 
	dsahern@...nel.org, Xuanqiang Luo <luoxuanqiang@...inos.cn>
Subject: Re: [PATCH net-next v8 3/3] inet: Avoid ehash lookup race in inet_twsk_hashdance_schedule()

On Tue, Oct 14, 2025 at 7:04 PM <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.
>
> 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")
> Reviewed-by: Kuniyuki Iwashima <kuniyu@...gle.com>
> Reviewed-by: Jiayuan Chen <jiayuan.chen@...ux.dev>
> Signed-off-by: Xuanqiang Luo <luoxuanqiang@...inos.cn>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>