linux-kernel - Re: [PATCH 1/1 v2] media: dib9000: avoid out of bound access

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Date:	Thu, 19 Jun 2014 09:34:34 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Heinrich Schuchardt <xypron.glpk@....de>
Cc:	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Michael Krufky <mkrufky@...uxtv.org>,
	linux-media@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1 v2] media: dib9000: avoid out of bound access

On Thu, Jun 19, 2014 at 7:49 AM, Heinrich Schuchardt <xypron.glpk@....de> wrote:
> This updated patch also fixes out of bound access to b[].
>
> In dib9000_risc_apb_access_write() an out of bound access to mb[].
>
> The current test to avoid out of bound access to mb[] is insufficient.
> For len = 19 non-existent mb[10] will be accessed.
>
> For odd values of len b[] is accessed out of bounds.
>
> For large values of len an of bound access to mb[] may occur in
> dib9000_mbx_send_attr.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@....de>
> ---
>  drivers/media/dvb-frontends/dib9000.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/dvb-frontends/dib9000.c b/drivers/media/dvb-frontends/dib9000.c
> index e540cfb..f75dec4 100644
> --- a/drivers/media/dvb-frontends/dib9000.c
> +++ b/drivers/media/dvb-frontends/dib9000.c
> @@ -1040,13 +1040,18 @@ static int dib9000_risc_apb_access_write(struct dib9000_state *state, u32 addres
>         if (address >= 1024 || !state->platform.risc.fw_is_running)
>                 return -EINVAL;
>
> +       if (len > 18)
> +               return -EINVAL;
> +
>         /* dprintk( "APB access thru wr fw %d %x", address, attribute); */
>
> -       mb[0] = (unsigned short)address;
> -       for (i = 0; i < len && i < 20; i += 2)
> -               mb[1 + (i / 2)] = (b[i] << 8 | b[i + 1]);
> +       mb[0] = (u16)address;
> +       for (i = 0; i + 1 < len; i += 2)
> +               mb[1 + i / 2] = b[i] << 8 | b[i + 1];
> +       if (len & 1)
> +               mb[1 + len / 2] = b[len - 1] << 8;
>
> -       dib9000_mbx_send_attr(state, OUT_MSG_BRIDGE_APB_W, mb, 1 + len / 2, attribute);
> +       dib9000_mbx_send_attr(state, OUT_MSG_BRIDGE_APB_W, mb, (3 + len) / 2, attribute);
>         return dib9000_mbx_get_message_attr(state, IN_MSG_END_BRIDGE_APB_RW, mb, &s, attribute) == 1 ? 0 : -EINVAL;
>  }
>
> --
> 2.0.0
>

That looks great, thanks!

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees


-- 
Kees Cook
Chrome OS Security
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