netdev - Re: [PATCH RFC net] net: sockmap: avoid race between sock_map_destroy() and sk_psock

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Message-ID: <9c8146a5-c7fc-40ae-81bb-37a2c12c2384@yandex.ru>
Date: Thu, 12 Sep 2024 18:59:39 +0300
From: Dmitry Antipov <dmantipov@...dex.ru>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: John Fastabend <john.fastabend@...il.com>,
 Jakub Sitnicki <jakub@...udflare.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 lvc-project@...uxtesting.org
Subject: Re: [PATCH RFC net] net: sockmap: avoid race between
 sock_map_destroy() and sk_psock_put()

On 9/11/24 7:45 PM, Cong Wang wrote:

> I guess you totally misunderstand my point. As a significant sockmap
> contributor, I am certainly aware of sockmap users. My point is that I
> needed to narrow down the problem to CONFIG_RDS when I was debugging it.

I've narrowed down the problem to possible race condition between two
functions. "Narrowing down" the problem to a 17.5Kloc-sized subsystem
is not too helpful.

> So, please let me know if you can still reproduce this after disabling
> CONFIG_RDS, because I could not reproduce it any more. If you can,
> please kindly share the stack trace without rds_* functions.

Yes, this issue requires CONFIG_RDS and CONFIG_RDS_TCP to reproduce. But
syzbot reproducer I'm working with doesn't create RDS sockets explicitly
(with 'socket(AF_RDS, ..., ...)' or so). When two options above are enabled,
the default network namespace has special kernel-space socket which is
created in 'rds_tcp_listen_init()' and (if my understanding of the namespaces
is correct) may be inherited with 'unshare(CLONE_NEWNET)'. So just enabling
these two options makes the kernel vulnerable.

So I'm still gently asking you to check whether there is a race condition
I've talked about. Hopefully this shouldn't be too hard for a significant
sockmap contributor.

Dmitry