linux-kernel - Re: [PATCH 4.4 246/268] media: cx25821: prevent out-of-bounds read on array card

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Message-ID: <1529279007.2289.246.camel@codethink.co.uk>
Date:   Mon, 18 Jun 2018 00:43:27 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Colin Ian King <colin.king@...onical.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc:     stable@...r.kernel.org,
        Sasha Levin <alexander.levin@...rosoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4.4 246/268] media: cx25821: prevent out-of-bounds read
 on array card

On Mon, 2018-05-28 at 12:03 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Colin Ian King <colin.king@...onical.com>
> 
> [ Upstream commit 67300abdbe9f1717532aaf4e037222762716d0f6 ]
> 
> Currently an out of range dev->nr is detected by just reporting the
> issue and later on an out-of-bounds read on array card occurs because
> of this. Fix this by checking the upper range of dev->nr with the size
> of array card (removes the hard coded size), move this check earlier
> and also exit with the error -ENOSYS to avoid the later out-of-bounds
> array read.

I don't think this is a correct fix.

The card[] array and module parameter appear to be completely
redundant.  Instead of arbitrarily limiting the number of cards that
the driver can bind to, we should remove them.

Ben.

> Detected by CoverityScan, CID#711191 ("Out-of-bounds-read")
> 
> Fixes: commit 02b20b0b4cde ("V4L/DVB (12730): Add conexant cx25821 driver")
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> Signed-off-by: Hans Verkuil <hans.verkuil@...co.com>
> [hans.verkuil@...co.com: %ld -> %zd]
> Signed-off-by: Mauro Carvalho Chehab <mchehab@...pensource.com>
> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/media/pci/cx25821/cx25821-core.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> --- a/drivers/media/pci/cx25821/cx25821-core.c
> +++ b/drivers/media/pci/cx25821/cx25821-core.c
> @@ -871,6 +871,10 @@ static int cx25821_dev_setup(struct cx25
>  	dev->nr = ++cx25821_devcount;
>  	sprintf(dev->name, "cx25821[%d]", dev->nr);
>  
> +	if (dev->nr >= ARRAY_SIZE(card)) {
> +		CX25821_INFO("dev->nr >= %zd", ARRAY_SIZE(card));
> +		return -ENODEV;
> +	}
>  	if (dev->pci->device != 0x8210) {
>  		pr_info("%s(): Exiting. Incorrect Hardware device = 0x%02x\n",
>  			__func__, dev->pci->device);
> @@ -886,9 +890,6 @@ static int cx25821_dev_setup(struct cx25
>  		dev->channels[i].sram_channels = &cx25821_sram_channels[i];
>  	}
>  
> -	if (dev->nr > 1)
> -		CX25821_INFO("dev->nr > 1!");
> -
>  	/* board config */
>  	dev->board = 1;		/* card[dev->nr]; */
>  	dev->_max_num_decoders = MAX_DECODERS;

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom