linux-kernel - Re: [PATCH 2/2] si2157: Bounds check firmware

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Message-ID: <CAAZRmGxi5ZZWEBKU3s0dfkqN1kdx1nYjguorcMpRv9_cVb4A7Q@mail.gmail.com>
Date:	Tue, 6 Oct 2015 00:24:59 +0200
From:	Olli Salonen <olli.salonen@....fi>
To:	Laura Abbott <labbott@...oraproject.org>
Cc:	Antti Palosaari <crope@....fi>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	linux-media <linux-media@...r.kernel.org>,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH 2/2] si2157: Bounds check firmware

Hi Laura,

While the patch itself does what it says, the return code for the
si2157_init will be 0 even if there's a faulty firmware file. Wouldn't
it be better to set the return code as -EINVAL like done a few lines
earlier in the code (see below)?

        if (fw->size % 17 != 0) {
                dev_err(&client->dev, "firmware file '%s' is invalid\n",
                                fw_name);
                ret = -EINVAL;
                goto err_release_firmware;
        }

Cheers,
-olli

On 30 September 2015 at 02:10, Laura Abbott <labbott@...oraproject.org> wrote:
> When reading the firmware and sending commands, the length
> must be bounds checked to avoid overrunning the size of the command
> buffer and smashing the stack if the firmware is not in the
> expected format. Add the proper check.
>
> Cc: stable@...nel.org
> Signed-off-by: Laura Abbott <labbott@...oraproject.org>
> ---
>  drivers/media/tuners/si2157.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/media/tuners/si2157.c b/drivers/media/tuners/si2157.c
> index 5073821..ce157ed 100644
> --- a/drivers/media/tuners/si2157.c
> +++ b/drivers/media/tuners/si2157.c
> @@ -166,6 +166,10 @@ static int si2157_init(struct dvb_frontend *fe)
>
>         for (remaining = fw->size; remaining > 0; remaining -= 17) {
>                 len = fw->data[fw->size - remaining];
> +               if (len > SI2157_ARGLEN) {
> +                       dev_err(&client->dev, "Bad firmware length\n");
> +                       goto err_release_firmware;
> +               }
>                 memcpy(cmd.args, &fw->data[(fw->size - remaining) + 1], len);
>                 cmd.wlen = len;
>                 cmd.rlen = 1;
> --
> 2.4.3
>
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