linux-kernel - [PATCH v3] [media] v4l2-common: fix overflow in v4l_bound_align

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Date:	Mon, 15 Sep 2014 10:14:48 +0200
From:	Maciej Matraszek <m.matraszek@...sung.com>
To:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>
Cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Maciej Matraszek <m.matraszek@...sung.com>,
	stable@...r.kernel.org
Subject: [PATCH v3] [media] v4l2-common: fix overflow in v4l_bound_align_image()

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@...sung.com>
Acked-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: <stable@...r.kernel.org>

---
v2: use clamp() instead of clamp_t(), as suggested by Sakari
v3: correct way of submitting patches for inclusion in the stable tree

 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..2e9d81f4c1a5 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(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

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