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Date:   Tue, 7 Nov 2017 08:31:05 -0200
From:   Mauro Carvalho Chehab <mchehab@s-opensource.com>
To:     Matthias Schwarzott <zzam@gentoo.org>,
        Andrey Konovalov <andreyknvl@google.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Max Kellermann <max.kellermann@gmail.com>,
        linux-media@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Kostya Serebryany <kcc@google.com>,
        syzkaller <syzkaller@googlegroups.com>
Subject: Re: usb/media/dtt200u: use-after-free in __dvb_frontend_free
Message-ID: <20171107083105.6998b182@vento.lan>
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        <c4ad7f4e-c838-aa44-5f0d-f8072ed41904@gentoo.org>
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Em Mon, 23 Oct 2017 20:58:09 +0200
Matthias Schwarzott <zzam@gentoo.org> escreveu:

> 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?

The problem with (1) is that drivers may need to use frontend_priv
on their own release callbacks.

So, I don't think this is the right fix.

I guess option (2) is the best one here.

Andrey,

Could you please test the enclosed patch?

Thanks!
Mauro

dvb_frontend: don't use-after-free the frontend struct

dvb_frontend_invoke_release() may free the frontend struct.
So, we can't update it anymore after calling it.
That's OK, as __dvb_frontend_free() is called only when the
krefs are zeroed, so nobody is using it anymore.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>


diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index daaf969719e4..80191a15cd89 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -153,7 +153,6 @@ static void __dvb_frontend_free(struct dvb_frontend *fe)
 	dvb_frontend_invoke_release(fe, fe->ops.release);
 
 	kfree(fepriv);
-	fe->frontend_priv = NULL;
 }
 
 static void dvb_frontend_free(struct kref *ref)


Thanks,
Mauro

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