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

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Date:   Tue, 28 Jul 2020 11:00:16 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Peilin Ye <yepeilin.cs@...il.com>
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>
Subject: Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix
 kernel-infoleak in video_put_user()

On Tue, Jul 28, 2020 at 12:05 AM Peilin Ye <yepeilin.cs@...il.com> wrote:
>
> On Mon, Jul 27, 2020 at 04:16:08PM +0300, Dan Carpenter wrote:
> > drivers/char/hpet.c:675 hpet_ioctl() warn: check that 'info' doesn't leak information (struct has a hole after 'hi_timer')
>
> This one seems like a false positive.
>
> drivers/char/hpet.c:670:
>
>         mutex_lock(&hpet_mutex);
>         err = hpet_ioctl_common(file->private_data, cmd, arg, &info);
>         mutex_unlock(&hpet_mutex);
>
>         if ((cmd == HPET_INFO) && !err &&
>             (copy_to_user((void __user *)arg, &info, sizeof(info))))
>                 err = -EFAULT;
>
> `info` is only being copied to userspace when `cmd` is `HPET_INFO`.
> However, hpet_ioctl_common() is already doing memset() on `info` in
> `case HPET_INFO`:
>
> drivers/char/hpet.c:612:
>
>         case HPET_INFO:
>                 {
>                         memset(info, 0, sizeof(*info));
>                         ^^^^^^

Yes, makes sense.

      Arnd