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

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Date:   Wed, 14 Feb 2018 16:11:57 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     syzbot <syzbot+bbd8e9a06452cc48059b@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>, linux-rdma@...r.kernel.org,
        netdev <netdev@...r.kernel.org>, rds-devel@....oracle.com,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in rds_tcp_tune

On Fri, Jan 12, 2018 at 7:30 PM, Sowmini Varadhan
<sowmini.varadhan@...cle.com> wrote:
> On (01/11/18 21:29), syzbot wrote:
>> ==================================================================
>> BUG: KASAN: use-after-free in rds_tcp_tune+0x491/0x520 net/rds/tcp.c:397
>> Read of size 4 at addr ffff8801cd5f6c58 by task kworker/u4:4/4954
>
> Just had an offline discussion with santosh around this, here's a summary
> of that discussion for the archives:
>
> Looks like an rds_connect_worker workq got scheduled after the
> netns was deleted. This could happen if an an rds_connection got
> added between lines 528 and 529 of
>
>   506 static void rds_tcp_kill_sock(struct net *net)
>   :
>   /* code to pull out all the rds_connections that should be destroyed */
>   :
>   528         spin_unlock_irq(&rds_tcp_conn_lock);
>   529         list_for_each_entry_safe(tc, _tc, &tmp_list, t_tcp_node)
>   530                 rds_conn_destroy(tc->t_cpath->cp_conn);
>
> Such an rds_connection would miss out the rds_conn_destroy()
> loop (that cancels all pending work) and (if it was scheduled
> after netns deletion) could trigger the use-after-free.
>
> Evaluating various fixes for this (including using _bh instead of _irq
> as suggested by santosh), I'll get back with a patch soon.


Hi Sowmini,

Was this ever fixed? What's the fix? This still hangs as open. Please
provide "syz fix" tag.