netdev - Re: [Patch net v2] tipc: fix a null pointer deref on error path

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Message-Id: <20171204.144800.504662839749640172.davem@davemloft.net>
Date:   Mon, 04 Dec 2017 14:48:00 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     xiyou.wangcong@...il.com
Cc:     netdev@...r.kernel.org, tipc-discussion@...ts.sourceforge.net,
        jon.maloy@...csson.com, ying.xue@...driver.com
Subject: Re: [Patch net v2] tipc: fix a null pointer deref on error path

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Mon, 4 Dec 2017 11:23:13 -0800

> On Mon, Dec 4, 2017 at 10:57 AM, David Miller <davem@...emloft.net> wrote:
>> From: Cong Wang <xiyou.wangcong@...il.com>
>> Date: Mon,  4 Dec 2017 10:31:43 -0800
>>
>>> In tipc_topsrv_kern_subscr() when s->tipc_conn_new() fails
>>> we call tipc_close_conn() to clean up, but in this case
>>> calling conn_put() is just enough.
>>>
>>> This fixes the folllowing crash:
>>  ...
>>> Fixes: 14c04493cb77 ("tipc: add ability to order and receive topology events in driver")
>>> Reported-by: syzbot <syzkaller@...glegroups.com>
>>> Cc: Jon Maloy <jon.maloy@...csson.com>
>>> Cc: Ying Xue <ying.xue@...driver.com>
>>> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
>>  ...
>>> @@ -511,7 +511,7 @@ bool tipc_topsrv_kern_subscr(struct net *net, u32 port, u32 type,
>>>       s = con->server;
>>>       scbr = s->tipc_conn_new(*conid);
>>>       if (!scbr) {
>>> -             tipc_close_conn(con);
>>> +             conn_put(con);
>>>               return false;
>>>       }
>>>
>>> --
>>> 2.13.0
>>>
>>
>> It looks like tipc_accept_from_sock() has a similar problem?  The
>> tipc_close_conn() will get invoked indirectly from the sock_release()
>> path right?
> 
> Not sure, the sock_release() in tipc_accept_from_sock() is for
> kernel_accept(), not for tipc_alloc_conn(). Or maybe it is hiding
> deep in the call chain that I miss?

I guess I'm trying to figure out where 'newcon' is released when the
call to s->tipc_conn_new() on it fails.

It looks similar to the situation you are fixing here, which is why I
am mentioning it.