Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix kernel-infoleak in video_put_user()

[Arnd Bergmann <arnd@arndb.de>]

On Mon, Jul 27, 2020 at 3:16 PM Dan Carpenter <dan.carpenter@oracle.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@gmail.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@syzkaller.appspotmail.com
> > > Link: https://syzkaller.appspot.com/bug?extid=79d751604cb6f29fbf59
> > > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > Signed-off-by: Peilin Ye <yepeilin.cs@gmail.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.

     Arnd
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