linux-kernel - Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix kernel-infoleak in video_put

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Date:   Mon, 27 Jul 2020 10:14:16 -0400
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Vandana BN <bnvandana@...il.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix
 kernel-infoleak in video_put_user()

On Mon, Jul 27, 2020 at 04:05:38PM +0200, Arnd Bergmann wrote:
> On Mon, Jul 27, 2020 at 3:16 PM Dan Carpenter <dan.carpenter@...cle.com> wrote:
> >
> > On Mon, Jul 27, 2020 at 09:25:16AM +0200, Arnd Bergmann wrote:
> > > On Mon, Jul 27, 2020 at 12:28 AM Peilin Ye <yepeilin.cs@...il.com> wrote:
> > > >
> > > > video_put_user() is copying uninitialized stack memory to userspace due
> > > > to the compiler not initializing holes in the structures declared on the
> > > > stack. Fix it by initializing `ev32` and `vb32` using memset().
> > > >
> > > > Reported-and-tested-by: syzbot+79d751604cb6f29fbf59@...kaller.appspotmail.com
> > > > Link: https://syzkaller.appspot.com/bug?extid=79d751604cb6f29fbf59
> > > > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > > > Signed-off-by: Peilin Ye <yepeilin.cs@...il.com>
> > >
> > > Thanks a lot for addressing this! I now see that I actually created a similar
> > > bugfix for it back in January, but for some reason that got stuck in my
> > > backlog and I never wrote a proper description for it or sent it out to the
> > > list, sorry about that. I would hope we could find a way to have either
> > > the compiler or sparse warn if we copy uninitialized data to user space,
> > > but we now don't even check for that within the kernel any more.
> >
> > Here are my latest warnings on linux-next from Friday.
> 
> Ah, I forgot you had that kind of list already, thanks for checking!
> 
> > block/scsi_ioctl.c:707 scsi_put_cdrom_generic_arg() warn: check that 'cgc32' doesn't leak information (struct has a hole after 'data_direction')
> 
> I see no padding in this one, should be fine AFAICT. Any idea why you
> get a warning
> for this instance?
> 
> > drivers/input/misc/uinput.c:743 uinput_ff_upload_to_user() warn: check that 'ff_up_compat' doesn't leak information (struct has a hole after 'replay')
> 
> This one hs padding in it and looks broken.
> 
> > drivers/input/misc/uinput.c:958 uinput_ioctl_handler() warn: check that 'ff_up' doesn't leak information (struct has a hole after 'replay')
> 
> hard to tell.
> 
> > drivers/firewire/core-cdev.c:463 ioctl_get_info() warn: check that 'bus_reset' doesn't leak information (struct has a hole after 'generation')
> 
> broken, trivial to fix
> 
> > drivers/scsi/megaraid/megaraid_mm.c:824 kioc_to_mimd() warn: check that 'cinfo.base' doesn't leak information
> 
> Seems fine due to __packed annotation.
> 
> > drivers/gpio/gpiolib-cdev.c:473 lineevent_read() warn: check that 'ge' doesn't leak information (struct has a hole after 'id')
> 
> The driver seems to initialize the elements correctly before putting
> them into the kfifo, so there is no infoleak. However the structure layout
> of "struct gpioevent_data" is incompatible between x86-32 and x86-64
> calling conventions, so this is likely broken in x86 compat mode,
> unless user space can explicitly deal with the difference.
> 
> > drivers/gpu/drm/i915/i915_query.c:136 query_engine_info() warn: check that 'query.num_engines' doesn't leak information
> 
> I don't think this leaks any state, as it just copies data to user space that
> it copied from there originally.
> 
> Stopping here for now.
> 
> Peilin Ye, is this something you are interested in fixing for the other drivers
> as well? I'd be happy to help review any further patches if you Cc me.

Yes, I would like to! I will start from:

	drivers/firewire/core-cdev.c:463
	drivers/input/misc/uinput.c:743

...as you mentioned above.

Thank you!
Peilin Ye