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

[Ben Hutchings]

On Mon, 2018-05-28 at 12:03 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.ÂÂIf anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> 
> [ 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@xxxxxxxxxxxxx>
> Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> [hans.verkuil@xxxxxxxxx: %ld -> %zd]
> Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> Âdrivers/media/pci/cx25821/cx25821-core.c |ÂÂÂÂ7 ++++---
> Â1 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
> Â	dev->nr = ++cx25821_devcount;
> Â	sprintf(dev->name, "cx25821[%d]", dev->nr);
> Â
> +	if (dev->nr >= ARRAY_SIZE(card)) {
> +		CX25821_INFO("dev->nr >= %zd", ARRAY_SIZE(card));
> +		return -ENODEV;
> +	}
> Â	if (dev->pci->device != 0x8210) {
> Â		pr_info("%s(): Exiting. Incorrect Hardware device = 0x%02x\n",
> Â			__func__, dev->pci->device);
> @@ -886,9 +890,6 @@ static int cx25821_dev_setup(struct cx25
> Â		dev->channels[i].sram_channels = &cx25821_sram_channels[i];
> Â	}
> Â
> -	if (dev->nr > 1)
> -		CX25821_INFO("dev->nr > 1!");
> -
> Â	/* board config */
> Â	dev->board = 1;		/* card[dev->nr]; */
> Â	dev->_max_num_decoders = MAX_DECODERS;

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