linux-kernel - Re: [PATCH v2] Fixing arbitrary kernel leak in case FBIOGETCMAP_SPARC in sbusfb_ioctl

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Message-ID: <CA+7wUsyy+g5evf0SQ+AWZdUzHR9uh1dBWYJm6z+c13XvVtyerw@mail.gmail.com>
Date:   Wed, 31 Jan 2018 16:49:10 +0100
From:   Mathieu Malaterre <malat@...ian.org>
To:     Peter Malone <peter.malone@...il.com>
Cc:     Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Fixing arbitrary kernel leak in case FBIOGETCMAP_SPARC
 in sbusfb_ioctl_helper().

Hi Peter,

On Wed, Jan 31, 2018 at 3:57 PM, Peter Malone <peter.malone@...il.com> wrote:
> Fixing arbitrary kernel leak in case FBIOGETCMAP_SPARC in
> sbusfb_ioctl_helper().
>
> 'index' is defined as an int in sbusfb_ioctl_helper().
> We retrieve this from the user:
> if (get_user(index, &c->index) ||
>     __get_user(count, &c->count) ||
>     __get_user(ured, &c->red) ||
>     __get_user(ugreen, &c->green) ||
>     __get_user(ublue, &c->blue))
>        return -EFAULT;
>
> and then we use 'index' in the following way:
> red = cmap->red[index + i] >> 8;
> green = cmap->green[index + i] >> 8;
> blue = cmap->blue[index + i] >> 8;
>
> This is a classic information leak vulnerability. 'index' should be
> an unsigned int, given its usage above.
>
> This patch is straight-forward; it changes 'index' to unsigned int
> in two switch-cases: FBIOGETCMAP_SPARC && FBIOPUTCMAP_SPARC.
>
> Signed-off-by: Peter Malone <peter.malone@...il.com>
> ---

much better :)

> v2: fixed formatting
>
>  drivers/video/fbdev/sbuslib.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fbdev/sbuslib.c b/drivers/video/fbdev/sbuslib.c
> index af6fc97f4ba4..a436d44f1b7f 100644
> --- a/drivers/video/fbdev/sbuslib.c
> +++ b/drivers/video/fbdev/sbuslib.c
> @@ -122,7 +122,7 @@ int sbusfb_ioctl_helper(unsigned long cmd, unsigned long arg,
>                 unsigned char __user *ured;
>                 unsigned char __user *ugreen;
>                 unsigned char __user *ublue;
> -               int index, count, i;
> +               unsigned int index, count, i;
>
>                 if (get_user(index, &c->index) ||
>                     __get_user(count, &c->count) ||
> @@ -161,7 +161,7 @@ int sbusfb_ioctl_helper(unsigned long cmd, unsigned long arg,
>                 unsigned char __user *ugreen;
>                 unsigned char __user *ublue;
>                 struct fb_cmap *cmap = &info->cmap;
> -               int index, count, i;
> +               unsigned int index, count, i;
>                 u8 red, green, blue;
>
>                 if (get_user(index, &c->index) ||
> --
> 2.14.3
>

By just looking at the code and commit message:

Acked-by: Mathieu Malaterre <malat@...ian.org>