Date:   Tue, 24 Oct 2017 13:19:18 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Matthias Schwarzott <zzam@...too.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Max Kellermann <max.kellermann@...il.com>,
        linux-media@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: usb/media/dtt200u: use-after-free in __dvb_frontend_free

On Mon, Oct 23, 2017 at 8:58 PM, Matthias Schwarzott <zzam@...too.org> wrote:
> Am 23.10.2017 um 16:41 schrieb Andrey Konovalov:
>> Hi!
>>
>> I've got the following report while fuzzing the kernel with syzkaller.
>>
>> On commit 3e0cc09a3a2c40ec1ffb6b4e12da86e98feccb11 (4.14-rc5+).
>>
>> dvb-usb: found a 'WideView WT-220U PenType Receiver (based on ZL353)'
>> in warm state.
>> dvb-usb: bulk message failed: -22 (2/1102416563)
>> dvb-usb: will use the device's hardware PID filter (table count: 15).
>> dvbdev: DVB: registering new adapter (WideView WT-220U PenType
>> Receiver (based on ZL353))
>> usb 1-1: media controller created
>> dvbdev: dvb_create_media_entity: media entity 'dvb-demux' registered.
>> usb 1-1: DVB: registering adapter 0 frontend 0 (WideView USB DVB-T)...
>> dvbdev: dvb_create_media_entity: media entity 'WideView USB DVB-T' registered.
>> Registered IR keymap rc-dtt200u
>> rc rc1: IR-receiver inside an USB DVB receiver as
>> /devices/platform/dummy_hcd.0/usb1/1-1/rc/rc1
>> input: IR-receiver inside an USB DVB receiver as
>> /devices/platform/dummy_hcd.0/usb1/1-1/rc/rc1/input9
>> dvb-usb: schedule remote query interval to 300 msecs.
>> dvb-usb: WideView WT-220U PenType Receiver (based on ZL353)
>> successfully initialized and connected.
>> dvb-usb: bulk message failed: -22 (1/1807119384)
>> dvb-usb: error -22 while querying for an remote control event.
>> dvb-usb: bulk message failed: -22 (1/1807119384)
>> dvb-usb: error -22 while querying for an remote control event.
>> dvb-usb: bulk message failed: -22 (1/1807119384)
>> dvb-usb: error -22 while querying for an remote control event.
>> dvb-usb: bulk message failed: -22 (1/1807119384)
>> dvb-usb: error -22 while querying for an remote control event.
>> dvb-usb: bulk message failed: -22 (1/1807119384)
>> dvb-usb: error -22 while querying for an remote control event.
>> dvb-usb: bulk message failed: -22 (1/1807119384)
>> dvb-usb: error -22 while querying for an remote control event.
>> usb 1-1: USB disconnect, device number 2
>> ==================================================================
>> BUG: KASAN: use-after-free in __dvb_frontend_free+0x113/0x120
>> Write of size 8 at addr ffff880067d45a00 by task kworker/0:1/24
>>
>> CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.14.0-rc5-43687-g06ab8a23e0e6 #545
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> Workqueue: usb_hub_wq hub_event
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:16
>>  dump_stack+0x292/0x395 lib/dump_stack.c:52
>>  print_address_description+0x78/0x280 mm/kasan/report.c:252
>>  kasan_report_error mm/kasan/report.c:351
>>  kasan_report+0x23d/0x350 mm/kasan/report.c:409
>>  __asan_report_store8_noabort+0x1c/0x20 mm/kasan/report.c:435
>>  __dvb_frontend_free+0x113/0x120 drivers/media/dvb-core/dvb_frontend.c:156
>>  dvb_frontend_put+0x59/0x70 drivers/media/dvb-core/dvb_frontend.c:176
>>  dvb_frontend_detach+0x120/0x150 drivers/media/dvb-core/dvb_frontend.c:2803
>>  dvb_usb_adapter_frontend_exit+0xd6/0x160
>> drivers/media/usb/dvb-usb/dvb-usb-dvb.c:340
>>  dvb_usb_adapter_exit drivers/media/usb/dvb-usb/dvb-usb-init.c:116
>>  dvb_usb_exit+0x9b/0x200 drivers/media/usb/dvb-usb/dvb-usb-init.c:132
>>  dvb_usb_device_exit+0xa5/0xf0 drivers/media/usb/dvb-usb/dvb-usb-init.c:295
>>  usb_unbind_interface+0x21c/0xa90 drivers/usb/core/driver.c:423
>>  __device_release_driver drivers/base/dd.c:861
>>  device_release_driver_internal+0x4f1/0x5c0 drivers/base/dd.c:893
>>  device_release_driver+0x1e/0x30 drivers/base/dd.c:918
>>  bus_remove_device+0x2f4/0x4b0 drivers/base/bus.c:565
>>  device_del+0x5c4/0xab0 drivers/base/core.c:1985
>>  usb_disable_device+0x1e9/0x680 drivers/usb/core/message.c:1170
>>  usb_disconnect+0x260/0x7a0 drivers/usb/core/hub.c:2124
>>  hub_port_connect drivers/usb/core/hub.c:4754
>>  hub_port_connect_change drivers/usb/core/hub.c:5009
>>  port_event drivers/usb/core/hub.c:5115
>>  hub_event+0x1318/0x3740 drivers/usb/core/hub.c:5195
>>  process_one_work+0xc73/0x1d90 kernel/workqueue.c:2119
>>  worker_thread+0x221/0x1850 kernel/workqueue.c:2253
>>  kthread+0x363/0x440 kernel/kthread.c:231
>>  ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>>
> It looks like this is caused by commit
> ead666000a5fe34bdc82d61838e4df2d416ea15e ("media: dvb_frontend: only use
> kref after initialized").
>
> The writing to "fe->frontend_priv" in dvb_frontend.c:156 is a
> use-after-free in case the object dvb_frontend *fe is already freed by
> the release callback called in line 153.
> Only if the demod driver is based on new style i2c_client the memory is
> still accessible.
>
> There are two possible solutions:
> 1. Clear fe->frontend_priv earlier (before line 153).
> 2. Do not clear fe->frontend_priv
>
> Can you try if the following patch (solution 1) fixes the issue?

Hi Matthias,

Your patch fixes the issue.

Thanks!

Tested-by: Andrey Konovalov <andreyknvl@...gle.com>

>
> Regards
> Matthias
>
> diff --git a/drivers/media/dvb-core/dvb_frontend.c
> b/drivers/media/dvb-core/dvb_frontend.c
> index daaf969719e4..f552acdb7d8c 100644
> --- a/drivers/media/dvb-core/dvb_frontend.c
> +++ b/drivers/media/dvb-core/dvb_frontend.c
> @@ -150,10 +150,11 @@ static void __dvb_frontend_free(struct
> dvb_frontend *fe)
>
>         dvb_free_device(fepriv->dvbdev);
>
> +       fe->frontend_priv = NULL;
> +
>         dvb_frontend_invoke_release(fe, fe->ops.release);
>
>         kfree(fepriv);
> -       fe->frontend_priv = NULL;
>  }
>
>  static void dvb_frontend_free(struct kref *ref)

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