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From: Rustam Kovhaev <>
To: Jason Gunthorpe <>
Subject: Re: KASAN: use-after-free Read in netdevice_event_work_handler
Date: Tue, 4 Aug 2020 13:00:13 -0700
Message-ID: <20200804200013.GB263814@thinkpad> (raw)
In-Reply-To: <>

On Sun, Aug 02, 2020 at 07:22:26PM -0300, Jason Gunthorpe wrote:
> On Fri, Jul 31, 2020 at 02:11:22PM -0700, Rustam Kovhaev wrote:
> > IB roce driver receives NETDEV_UNREGISTER event, calls dev_hold() and
> > schedules work item to execute, and before wq gets a chance to complete
> > it, we return to ip_tunnel.c:274 and call free_netdev(), and then later
> > we get UAF when scheduled function references already freed net_device
> > 
> > i added verbose logging to ip_tunnel.c to see pcpu_refcnt:
> > +       pr_info("about to free_netdev(dev) dev->pcpu_refcnt %d", netdev_refcnt_read(dev));
> > 
> > and got the following:
> > [  410.220127][ T2944] ip_tunnel: about to free_netdev(dev) dev->pcpu_refcnt 8
> I think there is a missing call to netdev_wait_allrefs() in the
> rollback_registered_many().
calling it there leads to rtnl deadlock, i think we should call
net_set_todo(), so that later when we call rtnl_unlock() it will
execute netdev_run_todo() and there it will proceed to calling
netdev_wait_allrefs(), but in ip tunnel i will need get
free_netdev() to be called after we unlock rtnl mutex
i'll try to send a new patch for review

> The normal success flow has this wait after delivering
> NETDEV_UNREGISTER, the error unwind for register_netdevice should as
> well.
> If the netdevice can progress to free while a dev_hold is active I
> think it means dev_hold is functionally useless.
good point

  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-09 23:54 syzbot
2020-07-22 20:29 ` syzbot
2020-07-31 21:11 ` Rustam Kovhaev
2020-08-01  2:23   ` Rustam Kovhaev
2020-08-02 22:22   ` Jason Gunthorpe
2020-08-04 20:00     ` Rustam Kovhaev [this message]
2020-08-05 15:20       ` Jason Gunthorpe
     [not found] <20200731211122.GA1728751 () thinkpad>
2020-08-01  2:06 ` Coiby Xu

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