linux-kernel - Re: [PATCH v4 0/8] y2038 safety in v4l2

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Date:   Mon, 25 Nov 2019 17:02:41 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Arnd Bergmann <arnd@...db.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, y2038@...ts.linaro.org
Subject: Re: [PATCH v4 0/8] y2038 safety in v4l2

Hi Arnd,

On 11/11/19 9:38 PM, Arnd Bergmann wrote:
> I'm in the process of finishing up the last bits on y2038-unsafe
> code in the kernel, this series is for v4l2, which has no problem
> with overflow, but has multiple ioctls that break with user space
> built against a new 32-bit libc.

Thank you for working on this. Much appreciated!

I've reviewed this v4 series and found a few issues (mostly things
that ended up in videodev2.h that shouldn't be there).

Once a v5 is posted I'll try to test this more.

Is there an easy(-ish) way to test this with a time64 ABI? Do you
have such an environment set up for testing?

> 
> I posted similar patches as part of a series back in 2015, the
> new version was rewritten from scratch and I double-checked with
> the old version to make sure I did not miss anything I had already
> taken care of before.
> 
> Hans Verkuil worked on a different patch set in 2017, but this
> also did not get to the point of being merged.
> 
> My new version contains compat-ioctl support, which the old one
> did not and should be complete, but given its size likely contains
> bugs. I did randconfig build tests, but no runtime test, so
> careful review as well as testing would be much appreciated.
> 
> With this version, the newly added code takes care of the existing
> ABI, while the existing code got moved to the 64-bit time_t
> interface and is used internally. This means that testing with
> existing binaries should exercise most of the modifications
> and if that works and doesn't get shot down in review, we can
> probably live without testing the new ABI explicitly.
> 
> I'm not entirely happy with the compat-ioctl implementation that
> adds quite a bit of code duplication, but I hope this is
> acceptable anyway, as a better implementation would likely
> require a larger refactoring of the compat-ioctl file, while
> my approach simply adds support for the additional data structure
> variants.

A cleanup is indeed much more work. This y2038 code is awful, but that's
really because the original structs are aligned in the worst possible
way.

Regards,

	Hans

> 
> This is a minor update compared to version 3 of this series,
> with bugfixes for small mistakes that I found or that were
> reported by automated build bots. I updated the tree at [2]
> to this version now.
> 
>       Arnd
> 
> [1] https://lwn.net/Articles/657754/
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/arnd/playground.git/log/?h=y2038-v4l2
> 
> Arnd Bergmann (8):
>   media: documentation: fix video_event description
>   media: v4l2: abstract timeval handling in v4l2_buffer
>   media: v4l2-core: compat: ignore native command codes
>   media: v4l2-core: split out data copy from video_usercopy
>   media: v4l2-core: fix VIDIOC_DQEVENT for time64 ABI
>   media: v4l2-core: fix v4l2_buffer handling for time64 ABI
>   media: v4l2-core: fix compat VIDIOC_DQEVENT for time64 ABI
>   media: v4l2-core: fix compat v4l2_buffer handling for time64 ABI
> 
>  .../media/uapi/dvb/video-get-event.rst        |   2 +-
>  Documentation/media/uapi/dvb/video_types.rst  |   2 +-
>  .../media/common/videobuf2/videobuf2-v4l2.c   |   4 +-
>  drivers/media/pci/meye/meye.c                 |   4 +-
>  drivers/media/usb/cpia2/cpia2_v4l.c           |   4 +-
>  drivers/media/usb/stkwebcam/stk-webcam.c      |   2 +-
>  drivers/media/usb/usbvision/usbvision-video.c |   4 +-
>  drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 470 +++++++++++++++---
>  drivers/media/v4l2-core/v4l2-event.c          |   5 +-
>  drivers/media/v4l2-core/v4l2-ioctl.c          | 188 +++++--
>  drivers/media/v4l2-core/v4l2-subdev.c         |  20 +-
>  drivers/media/v4l2-core/videobuf-core.c       |   4 +-
>  include/linux/videodev2.h                     |  17 +-
>  include/trace/events/v4l2.h                   |   2 +-
>  include/uapi/linux/videodev2.h                |  77 +++
>  15 files changed, 669 insertions(+), 136 deletions(-)
>