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

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Message-ID: <CAK8P3a3NB2BVo9fH-Wcinrhhs-QJ=9dK59Ds83TvgLmEkRy3qA@mail.gmail.com>
Date:   Mon, 27 Jul 2020 09:25:16 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Peilin Ye <yepeilin.cs@...il.com>
Cc:     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>
Subject: Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix
 kernel-infoleak in video_put_user()

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.

I would suggest adding these tags to the patch, to ensure it gets backported
to stable kernels as needed:

Cc: stable@...r.kernel.org
Fixes: 1a6c0b36dd19 ("media: v4l2-core: fix VIDIOC_DQEVENT for time64 ABI")
Fixes: 577c89b0ce72 ("media: v4l2-core: fix v4l2_buffer handling for
time64 ABI")

In addition to

Reviewed-by: Arnd Bergmann <arnd@...db.de>