Re: [PATCH RFC net] net: sockmap: avoid race between sock_map_destroy() and sk_psock_put()

[Dmitry Antipov <dmantipov@yandex.ru>]

+CC Allison

On 9/14/24 3:34 AM, Cong Wang wrote:
> On Thu, Sep 12, 2024 at 06:59:39PM +0300, Dmitry Antipov wrote:
>> 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.
> 
> Narrowing down from more 30 millions lines of code to 17.5K is already a huge
> win to me, maybe not for you. :)
> 
>>
>>> 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.
> 
> Thanks for confirming it.
> 
> I did notice the RDS kernel socket, but, without my patch, we can still
> use sockops to hook TCP socket under the RDS socket and add it to a
> sockmap, hence the conflict of sock->sk->sk_user_data.
> 
> My patch basically prevents such TCP socket under RDS socket from being
> added to any sockmap.
> 
>>
>> 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.
> 
> If you can kindly explain why this race condition is not related to RDS
> despite the fact it only happens with CONFIG_RDS enabled, I'd happy to
> review it. Otherwise, I feel like you may head to a wrong direction.
> 
> Thanks.