Re: [PATCH v4] tun: fix use-after-free when register netdev failed

[David Miller <davem@davemloft.net>]

From: Yang Yingliang <yangyingliang@huawei.com>
Date: Tue, 10 Sep 2019 18:56:57 +0800

> I got a UAF repport in tun driver when doing fuzzy test:
 ...
> tun_chr_read_iter() accessed the memory which freed by free_netdev()
> called by tun_set_iff():
> 
>         CPUA                                           CPUB
>   tun_set_iff()
>     alloc_netdev_mqs()
>     tun_attach()
>                                                   tun_chr_read_iter()
>                                                     tun_get()
>                                                     tun_do_read()
>                                                       tun_ring_recv()
>     register_netdevice() <-- inject error
>     goto err_detach
>     tun_detach_all() <-- set RCV_SHUTDOWN
>     free_netdev() <-- called from
>                      err_free_dev path
>       netdev_freemem() <-- free the memory
>                         without check refcount
>       (In this path, the refcount cannot prevent
>        freeing the memory of dev, and the memory
>        will be used by dev_put() called by
>        tun_chr_read_iter() on CPUB.)
>                                                      (Break from tun_ring_recv(),
>                                                      because RCV_SHUTDOWN is set)
>                                                    tun_put()
>                                                      dev_put() <-- use the memory
>                                                                    freed by netdev_freemem()
> 
> Put the publishing of tfile->tun after register_netdevice(),
> so tun_get() won't get the tun pointer that freed by
> err_detach path if register_netdevice() failed.
> 
> Fixes: eb0fb363f920 ("tuntap: attach queue 0 before registering netdevice")
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Suggested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>

Applied, thanks.