[PATCH] [media] v4l2-common: fix overflow in v4l_bound_align_image()

[PATCH] [media] v4l2-common: fix overflow in v4l_bound_align_image()

[Maciej Matraszek]

Fix clamp_align() used in v4l_bound_align_image() to prevent overflow when
passed large value like UINT32_MAX. In the current implementation:
    clamp_align(UINT32_MAX, 8, 8192, 3)
returns 8, because in line:
    x = (x + (1 << (align - 1))) & mask;
x overflows to (-1 + 4) & 0x7 = 3, while expected value is 8192.

v4l_bound_align_image() is heavily used in VIDIOC_S_FMT
and VIDIOC_SUBDEV_S_FMT ioctls handlers, and documentation of the latter
explicitly states that:

"The modified format should be as close as possible to the original request."
  -- http://linuxtv.org/downloads/v4l-dvb-apis/vidioc-subdev-g-fmt.html

Thus one would expect, that passing UINT32_MAX as format width and height
will result in setting maximum possible resolution for the device.
Particularly, when the driver doesn't support VIDIOC_ENUM_FRAMESIZES ioctl,
which is common in the codebase.

Fixes: b0d3159be9a3 ("V4L/DVB (11901): v4l2: Create helper function for bounding and aligning images")
Signed-off-by: Maciej Matraszek <m.matraszek@samsung.com>
---
 drivers/media/v4l2-core/v4l2-common.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
index ccaa38f65cf1..506cf8b7763b 100644
--- a/drivers/media/v4l2-core/v4l2-common.c
+++ b/drivers/media/v4l2-core/v4l2-common.c
@@ -435,16 +435,13 @@ static unsigned int clamp_align(unsigned int x, unsigned int min,
 	/* Bits that must be zero to be aligned */
 	unsigned int mask = ~((1 << align) - 1);
 
+	/* Clamp to aligned min and max */
+	x = clamp_t(unsigned int, x, (min + ~mask) & mask, max & mask);
+
 	/* Round to nearest aligned value */
 	if (align)
 		x = (x + (1 << (align - 1))) & mask;
 
-	/* Clamp to aligned value of min and max */
-	if (x < min)
-		x = (min + ~mask) & mask;
-	else if (x > max)
-		x = max & mask;
-
 	return x;
 }
 
-- 
1.9.1

Re: [PATCH] [media] v4l2-common: fix overflow in v4l_bound_align_image()

[Sakari Ailus]

Hi Maciej,

Thanks for the patch!

On Tue, Sep 09, 2014 at 05:16:41PM +0200, Maciej Matraszek wrote:
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index ccaa38f65cf1..506cf8b7763b 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -435,16 +435,13 @@ static unsigned int clamp_align(unsigned int x, unsigned int min,
>  	/* Bits that must be zero to be aligned */
>  	unsigned int mask = ~((1 << align) - 1);
>  
> +	/* Clamp to aligned min and max */
> +	x = clamp_t(unsigned int, x, (min + ~mask) & mask, max & mask);

I think you could use just clamp() since all the arguments are unsigned int.
With that considered,

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>

> +
>  	/* Round to nearest aligned value */
>  	if (align)
>  		x = (x + (1 << (align - 1))) & mask;
> 
> -	/* Clamp to aligned value of min and max */
> -	if (x < min)
> -		x = (min + ~mask) & mask;
> -	else if (x > max)
> -		x = max & mask;
> -
>  	return x;
>  }
>  

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@iki.fi	XMPP: sailus@retiisi.org.uk