netdev - Re: Crash due to destroying TCP request sockets using SOCK

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Date:   Fri, 6 Jul 2018 03:24:13 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Lorenzo Colitti <lorenzo@...gle.com>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Cc:     netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>,
        Alistair Strachan <astrachan@...gle.com>,
        David Ahern <dsa@...ulusnetworks.com>
Subject: Re: Crash due to destroying TCP request sockets using SOCK_DESTROY



On 07/05/2018 09:46 PM, Lorenzo Colitti wrote:
> On Fri, Jul 6, 2018 at 11:37 AM Subash Abhinov Kasiviswanathan
> <subashab@...eaurora.org> wrote:
>>
>>  From the call stack, a TCP socket is being destroyed using netlink_diag.
>> The memory dump showed that the socket was an inet request socket (in
>> state TCP_NEW_SYN_RECV) with refcount of 0.
>> [...]
>>   13232.479820:   <2> refcount_t: underflow; use-after-free.
>>   13232.479838:   <6> ------------[ cut here ]------------
>>   13232.479843:   <6> kernel BUG at kernel/msm-4.14/lib/refcount.c:204!
>>   13232.479849:   <6> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>> [...]
>>   13232.479996:   <6> Process netd (pid: 648, stack limit =
>> 0xffffff801cf98000)
>>   13232.479998:   <2> Call trace:
>>   13232.480000:   <2>  refcount_sub_and_test+0x64/0x78
>>   13232.480002:   <2>  refcount_dec_and_test+0x18/0x24
>>   13232.480005:   <2>  sock_gen_put+0x1c/0xb0
>>   13232.480009:   <2>  tcp_diag_destroy+0x54/0x68
>> [...]
> 
> Looks like for a TCP_NEW_SYN_RECV socket, sock_diag_destroy
> essentially ends up doing:
> 
>                         struct request_sock *req = inet_reqsk(sk);
> 
>                         local_bh_disable();
>                         inet_csk_reqsk_queue_drop_and_put(req->rsk_listener,
>                                                           req);
>                         local_bh_enable();
> ...
> 
>         sock_gen_put(sk);
> 
> It looks like inet_csk_reqsk_queue_drop_and_put calls reqsk_put(req),
> which frees the socket, and at that point sock_gen_put is a UAF. Do we
> just need:
> 
> -                        inet_csk_reqsk_queue_drop_and_put(req->rsk_listener,
> -                                                           req);
> +                        inet_csk_reqsk_queue_drop(req->rsk_listener, req);
> 
> since sock_gen_put will also end up calling reqsk_put() for a
> TCP_SYN_RECV socket?
> 
> Alastair - you're able to reproduce this UAF using net_test on qemu,
> right? If so, could you try that two-line patch above?
> 

Hi Lorenzo

Your patch makes sense to me, please submit it formally with :

Fixes: d7226c7a4dd1 ("net: diag: Fix refcnt leak in error path destroying socket")
Cc: David Ahern <dsa@...ulusnetworks.com>

Thanks !