netdev - Re: KASAN: use-after-free Read in rds_tcp_dev

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Date:   Tue, 14 Nov 2017 10:02:59 -0800
From:   Girish Moodalbail <girish.moodalbail@...cle.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     syzbot 
        <bot+643ecad3f5bb49700e839363b608c4928f6db8f0@...kaller.appspotmail.com>,
        davem@...emloft.net, netdev@...r.kernel.org,
        rds-devel@....oracle.com, santosh.shilimkar@...cle.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in rds_tcp_dev_event

On 11/14/17 5:22 AM, Sowmini Varadhan wrote:
> 
> 
> A few questions.
> 
> - First off, why am I not seeing the original mail in this thread
>    even when I search the mail archives, e.g.,
>      https://lkml.org/lkml/2017/11/13/954
> 
> -  Girish Moodalbail writes:
> 
>> The issue here is that we are trying to reference a network namespace
>> (struct net *) that is long gone (i.e., L532 below -- c_net is the culprit).
> 
>    The netns is not "long gone", we are still processing
>    the NETDEV_UNREGISTER_FINAL for loopback.

Obviously, I was not talking about the current namespace.

Say there are two namespaces - ns1 and ns2 and that both have RDS connections. 
Deletion of ns1 will be fine. However when ns2 is being deleted, in the 
rds_tcp_dev_event() callback we walk through the global list and some nodes in 
that list will be referring to ns1 (that is "long gone"). If you read my earlier 
email, I was talking about ns1 which is already gone, and we are trying to 
access it from ns2.

~Girish


> As I said in my
>    earlier mail, the idea is to extract the list of unique conns
>    that belong to the netns and then destroy both the conn, and
>    all associated paths. Thus there can only be a single thread
>    going through rds_tcp_kill_sock at any time (since we should
>    only get the unregister_final/loopback one time for the netns).
>    (See alos comment block in rds_tcp_dev_event about network activity
>    quiescing). Thus there should be no concurrency issue.
> 
>    However when I just ehecked this, there may be some rds connection
>    refcounting bug. When I quickly tested this, I'm not seeing the
>    expected calls to conn_path_destroy. I'll need some time to take
>    a look, this has been known to work, so something got broken along
>    the way
>   
>> I think we should move away from global list to a per-namespace list. The
>> global list are used only in two places (both of which are per-namespace
>> operations):
> 
> let's first understand the real root-cause before we start
> redesigning data-structures.
> 
> --Sowmini
> 
> 
>