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

From: Arnd Bergmann <arnd@arndb.de>
To: Peilin Ye <yepeilin.cs@gmail.com>
Cc: "Niklas Söderlund" <niklas.soderlund+renesas@ragnatech.se>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	"Linux Media Mailing List" <linux-media@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Laurent Pinchart" <laurent.pinchart@ideasonboard.com>,
	"Sakari Ailus" <sakari.ailus@linux.intel.com>,
	"Vandana BN" <bnvandana@gmail.com>,
	"Hans Verkuil" <hverkuil-cisco@xs4all.nl>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Ezequiel Garcia" <ezequiel@collabora.com>,
	"Dan Carpenter" <dan.carpenter@oracle.com>,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix kernel-infoleak in video_put_user()
Date: Tue, 28 Jul 2020 11:00:16 +0200	[thread overview]
Message-ID: <CAK8P3a0CcmchionPJQr_4Gdevo8r8ixed7WHSu8MyYvffagqdg@mail.gmail.com> (raw)
In-Reply-To: <20200727220456.GA328887@PWN>

On Tue, Jul 28, 2020 at 12:05 AM Peilin Ye <yepeilin.cs@gmail.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
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