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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 30 Jul 2020 10:15:24 +0200
Message-ID: <CAK8P3a1m7C0rGGEHvndhxun2TyFh-cweNnPHp-rDtu7Z=YyUKw@mail.gmail.com>
Subject: Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix
 kernel-infoleak in video_put_user()
To:     Bartosz Golaszewski <brgl@bgdev.pl>
Cc:     Dan Carpenter <dan.carpenter@oracle.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Peilin Ye <yepeilin.cs@gmail.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Vandana BN <bnvandana@gmail.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        =?UTF-8?Q?Niklas_S=C3=B6derlund?= 
        <niklas.soderlund+renesas@ragnatech.se>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
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On Thu, Jul 30, 2020 at 10:07 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> On Tue, Jul 28, 2020 at 3:58 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Tue, Jul 28, 2020 at 3:06 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > Something like
> >
> > static int lineevent_put_data(void __user *uptr, struct gpioevent_data *ge)
> > {
> > #ifdef __x86_64__
> >         /* i386 has no padding after 'id' */
> >         if (in_ia32_syscall()) {
> >                 struct {
> >                         compat_u64      timestamp __packed;
> >                         u32             id;
> >                 } compat_ge = { ge->timestamp, ge->id };
> >
> >                 if (copy_to_user(uptr, &compat_ge, sizeof(compat_ge)))
> >                         return -EFAULT;
> >
> >                 return sizeof(compat_ge);
> >         }
> > #endif
> >
> >         if (copy_to_user(uptr, ge, sizeof(*ge))
> >                 return -EFAULT;
> >
> >         return sizeof(*ge);
> > }
> >
> >        Arnd
>
> Hi Arnd,
>
> Andy actually had a patch for that but since this isn't a regression
> (it never worked), we decided to leave it as it is and get it right in
> v2 API.

I would argue that it needs to be fixed anyway, unless you also want
to remove the v1 interface for native mode. If this works on 32-bit
kernels, on 64-bit kernels with 64-bit user space and on compat
32-bit user space on 64-bit non-x86 architectures, I see no reason
to leave it broken specifically on x86 compat user space. There are
still reasons to use 32-bit x86 user space for low-memory machines
even though native i386 kernels are getting increasingly silly.

     Arnd