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Date:   Thu, 1 Aug 2019 06:09:15 +0100
From:   Sean Young <sean@mess.org>
To:     Michael Ira Krufky <mkrufky@linuxtv.org>
Cc:     Vandana BN <bnvandana@gmail.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        tskd08@gmail.com, skhan@linuxfoundation.org,
        gregkh@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [PATCH v2] media:dvb-frontends:Remove dvb_pll_devcount and id
 module parameters.
Message-ID: <20190801050915.bmv5xpbczixtaotf@gofer.mess.org>
References: <20190717141204.19433-1-bnvandana@gmail.com>
 <20190720061302.24047-1-bnvandana@gmail.com>
 <20190724053635.4pl44glggvcnton2@gofer.mess.org>
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On Wed, Jul 24, 2019 at 06:36:35AM +0100, Sean Young wrote:
> On Sat, Jul 20, 2019 at 11:43:02AM +0530, Vandana BN wrote:
> > Syzbot reported global-out-of-bounds Read in dvb_pll_attach, while
> > accessing id[dvb_pll_devcount], because dvb_pll_devcount was 65,
> > that is more than size of 'id' which is DVB_PLL_MAX(64).
> > 
> > Fix would be to check if DVB_PLL_MAX devices are attached and if so return
> > NULL from dvb_pll_attach(). But this will put a limit on the number of
> > devices that can be attached.
> > Also dvb_pll_devcount and "id" module parameter are used for debugging
> > purpose to override/force PLL type.
> > So this patch removes these module parameters.
> > 
> > Reported-by: syz...@syzkaller.appspotmail.com
> > 
> > usb 1-1: dvb_usb_v2: will pass the complete MPEG2 transport stream to the
> > software demuxer
> > dvbdev: DVB: registering new adapter (774 Friio White ISDB-T USB2.0)
> > usb 1-1: media controller created
> > dvbdev: dvb_create_media_entity: media entity 'dvb-demux' registered.
> > tc90522 0-0018: Toshiba TC90522 attached.
> > usb 1-1: DVB: registering adapter 0 frontend 0 (Toshiba TC90522 ISDB-T
> > module)...
> > dvbdev: dvb_create_media_entity: media entity 'Toshiba TC90522 ISDB-T
> > module' registered.
> > ==================================================================
> > BUG: KASAN: global-out-of-bounds in dvb_pll_attach+0x6c5/0x830
> > drivers/media/dvb-frontends/dvb-pll.c:798
> > Read of size 4 at addr ffffffff89c9e5e0 by task kworker/0:1/12
> > 
> > CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.2.0-rc6+ #13
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Workqueue: usb_hub_wq hub_event
> > Call Trace:
> >   __dump_stack lib/dump_stack.c:77 [inline]
> >   dump_stack+0xca/0x13e lib/dump_stack.c:113
> >   print_address_description+0x67/0x231 mm/kasan/report.c:188
> >   __kasan_report.cold+0x1a/0x32 mm/kasan/report.c:317
> >   kasan_report+0xe/0x20 mm/kasan/common.c:614
> >   dvb_pll_attach+0x6c5/0x830 drivers/media/dvb-frontends/dvb-pll.c:798
> >   dvb_pll_probe+0xfe/0x174 drivers/media/dvb-frontends/dvb-pll.c:877
> >   i2c_device_probe+0x790/0xaa0 drivers/i2c/i2c-core-base.c:389
> >   really_probe+0x281/0x660 drivers/base/dd.c:509
> >   driver_probe_device+0x104/0x210 drivers/base/dd.c:670
> >   __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:777
> >   bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454
> >   __device_attach+0x217/0x360 drivers/base/dd.c:843
> >   bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
> >   device_add+0xae6/0x16f0 drivers/base/core.c:2111
> >   i2c_new_client_device+0x5b3/0xc40 drivers/i2c/i2c-core-base.c:778
> >   i2c_new_device+0x19/0x50 drivers/i2c/i2c-core-base.c:821
> >   dvb_module_probe+0xf9/0x220 drivers/media/dvb-core/dvbdev.c:985
> >   friio_tuner_attach+0x125/0x1d0 drivers/media/usb/dvb-usb-v2/gl861.c:536
> >   dvb_usbv2_adapter_frontend_init
> > drivers/media/usb/dvb-usb-v2/dvb_usb_core.c:675 [inline]
> >   dvb_usbv2_adapter_init drivers/media/usb/dvb-usb-v2/dvb_usb_core.c:804
> > [inline]
> >   dvb_usbv2_init drivers/media/usb/dvb-usb-v2/dvb_usb_core.c:865 [inline]
> >   dvb_usbv2_probe.cold+0x24dc/0x255d
> > drivers/media/usb/dvb-usb-v2/dvb_usb_core.c:980
> >   usb_probe_interface+0x305/0x7a0 drivers/usb/core/driver.c:361
> >   really_probe+0x281/0x660 drivers/base/dd.c:509
> >   driver_probe_device+0x104/0x210 drivers/base/dd.c:670
> >   __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:777
> >   bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454
> >   __device_attach+0x217/0x360 drivers/base/dd.c:843
> >   bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
> >   device_add+0xae6/0x16f0 drivers/base/core.c:2111
> >   usb_set_configuration+0xdf6/0x1670 drivers/usb/core/message.c:2023
> >   generic_probe+0x9d/0xd5 drivers/usb/core/generic.c:210
> >   usb_probe_device+0x99/0x100 drivers/usb/core/driver.c:266
> >   really_probe+0x281/0x660 drivers/base/dd.c:509
> >   driver_probe_device+0x104/0x210 drivers/base/dd.c:670
> >   __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:777
> >   bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454
> >   __device_attach+0x217/0x360 drivers/base/dd.c:843
> >   bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
> >   device_add+0xae6/0x16f0 drivers/base/core.c:2111
> >   usb_new_device.cold+0x8c1/0x1016 drivers/usb/core/hub.c:2534
> >   hub_port_connect drivers/usb/core/hub.c:5089 [inline]
> >   hub_port_connect_change drivers/usb/core/hub.c:5204 [inline]
> >   port_event drivers/usb/core/hub.c:5350 [inline]
> >   hub_event+0x1ada/0x3590 drivers/usb/core/hub.c:5432
> >   process_one_work+0x905/0x1570 kernel/workqueue.c:2269
> >   process_scheduled_works kernel/workqueue.c:2331 [inline]
> >   worker_thread+0x7ab/0xe20 kernel/workqueue.c:2417
> >   kthread+0x30b/0x410 kernel/kthread.c:255
> >   ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> > 
> > The buggy address belongs to the variable:
> >   id+0x100/0x120
> > 
> > Memory state around the buggy address:
> >   ffffffff89c9e480: fa fa fa fa 00 00 fa fa fa fa fa fa 00 00 00 00
> >   ffffffff89c9e500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > ffffffff89c9e580: 00 00 00 00 00 00 00 00 00 00 00 00 fa fa fa fa
> >                                                         ^
> >   ffffffff89c9e600: 04 fa fa fa fa fa fa fa 04 fa fa fa fa fa fa fa
> >   ffffffff89c9e680: 04 fa fa fa fa fa fa fa 04 fa fa fa fa fa fa fa
> > ==================================================================
> > 
> > Signed-off-by: Vandana BN <bnvandana@gmail.com>
> > ---
> >  drivers/media/dvb-frontends/dvb-pll.c | 19 +++----------------
> >  1 file changed, 3 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/media/dvb-frontends/dvb-pll.c b/drivers/media/dvb-frontends/dvb-pll.c
> > index ba0c49107bd2..c3a04751e9cf 100644
> > --- a/drivers/media/dvb-frontends/dvb-pll.c
> > +++ b/drivers/media/dvb-frontends/dvb-pll.c
> > @@ -33,19 +33,11 @@ struct dvb_pll_priv {
> >  	u32 bandwidth;
> >  };
> > 
> > -#define DVB_PLL_MAX 64
> > -
> > -static unsigned int dvb_pll_devcount;
> > 
> >  static int debug;
> >  module_param(debug, int, 0644);
> >  MODULE_PARM_DESC(debug, "enable verbose debug messages");
> > 
> > -static unsigned int id[DVB_PLL_MAX] =
> > -	{ [ 0 ... (DVB_PLL_MAX-1) ] = DVB_PLL_UNDEFINED };
> > -module_param_array(id, int, NULL, 0644);
> > -MODULE_PARM_DESC(id, "force pll id to use (DEBUG ONLY)");
> > -
> 
> Mike, you introduced this module parameter in:
> 
> commit 05a4611b5d71ad6f968fdeef092c24914570898b
> Author:     Michael Krufky <mkrufky@linuxtv.org>
> AuthorDate: Fri Sep 7 18:19:57 2007 -0300
> 
>     V4L/DVB (6228): dvb-pll: add module option to specify rf input
>     
>     Add a module option to dvb-pll, called "input" to specify which rf
>     input to use on devices with multiple rf inputs.  If the module option
>     is not specified, then the driver will autoselect the rf input, as per
>     previous behavior.
>     
>     Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
>     Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
> 
> What was your motivation?

dvb_pll_devcount only ever gets increased, so this only works for the
first time a driver is loaded; after a usb replug or rmmod this does
not work anymore since the dvb_pll_devcount will have moved on to the
next entry. Considering it is broken maybe it should just be removed;
also we have no answer from mkrufky yet.

If this functionality is useful, then it should be implemented with
an DEFINE_IDA() and ida_simpla_get(), but I'm not sure it's worth it
when the functionality is probably unused. If it was used, someone
would have noticed it was broken.


Sean