[v4] media: s3c-camif: fix out-of-bounds array access

Message ID 20180116215242.784423-1-arnd@arndb.de
State New
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Series
  • [v4] media: s3c-camif: fix out-of-bounds array access
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Commit Message

Arnd Bergmann Jan. 16, 2018, 9:52 p.m.
While experimenting with older compiler versions, I ran
into a warning that no longer shows up on gcc-4.8 or newer:

drivers/media/platform/s3c-camif/camif-capture.c: In function '__camif_subdev_try_format':
drivers/media/platform/s3c-camif/camif-capture.c:1265:25: error: array subscript is below array bounds

This is an off-by-one bug, leading to an access before the start of the
array, while newer compilers silently assume this undefined behavior
cannot happen and leave the loop at index 0 if no other entry matches.

As Sylvester explains, we actually need to ensure that the
value is within the range, so this reworks the loop to be
easier to parse correctly, and an additional check to fall
back on the first format value for any unexpected input.

I found an existing gcc bug for it and added a reduced version
of the function there.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69249#c3
Fixes: babde1c243b2 ("[media] V4L: Add driver for S3C24XX/S3C64XX SoC series camera interface")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
v4: simplify a bit
v3: fix newly introduced off-by-one bug.
v2: rework logic rather than removing it.
---
 drivers/media/platform/s3c-camif/camif-capture.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

-- 
2.9.0

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Comments

Laurent Pinchart Jan. 16, 2018, 10:13 p.m. | #1
Hi Arnd,

Thank you for the patch.

On Tuesday, 16 January 2018 23:52:15 EET Arnd Bergmann wrote:
> While experimenting with older compiler versions, I ran

> into a warning that no longer shows up on gcc-4.8 or newer:

> 

> drivers/media/platform/s3c-camif/camif-capture.c: In function

> '__camif_subdev_try_format':

> drivers/media/platform/s3c-camif/camif-capture.c:1265:25: error: array

> subscript is below array bounds

> 

> This is an off-by-one bug, leading to an access before the start of the

> array, while newer compilers silently assume this undefined behavior

> cannot happen and leave the loop at index 0 if no other entry matches.

> 

> As Sylvester explains, we actually need to ensure that the

> value is within the range, so this reworks the loop to be

> easier to parse correctly, and an additional check to fall

> back on the first format value for any unexpected input.

> 

> I found an existing gcc bug for it and added a reduced version

> of the function there.

> 

> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69249#c3

> Fixes: babde1c243b2 ("[media] V4L: Add driver for S3C24XX/S3C64XX SoC series

> camera interface") Signed-off-by: Arnd Bergmann <arnd@arndb.de>


Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>


> ---

> v4: simplify a bit

> v3: fix newly introduced off-by-one bug.

> v2: rework logic rather than removing it.

> ---

>  drivers/media/platform/s3c-camif/camif-capture.c | 7 ++++---

>  1 file changed, 4 insertions(+), 3 deletions(-)

> 

> diff --git a/drivers/media/platform/s3c-camif/camif-capture.c

> b/drivers/media/platform/s3c-camif/camif-capture.c index

> 437395a61065..9ab8e7ee2e1e 100644

> --- a/drivers/media/platform/s3c-camif/camif-capture.c

> +++ b/drivers/media/platform/s3c-camif/camif-capture.c

> @@ -1256,16 +1256,17 @@ static void __camif_subdev_try_format(struct

> camif_dev *camif, {

>  	const struct s3c_camif_variant *variant = camif->variant;

>  	const struct vp_pix_limits *pix_lim;

> -	int i = ARRAY_SIZE(camif_mbus_formats);

> +	unsigned int i;

> 

>  	/* FIXME: constraints against codec or preview path ? */

>  	pix_lim = &variant->vp_pix_limits[VP_CODEC];

> 

> -	while (i-- >= 0)

> +	for (i = 0; i < ARRAY_SIZE(camif_mbus_formats); i++)

>  		if (camif_mbus_formats[i] == mf->code)

>  			break;

> 

> -	mf->code = camif_mbus_formats[i];

> +	if (i == ARRAY_SIZE(camif_mbus_formats))

> +		mf->code = camif_mbus_formats[0];

> 

>  	if (pad == CAMIF_SD_PAD_SINK) {

>  		v4l_bound_align_image(&mf->width, 8, CAMIF_MAX_PIX_WIDTH,



-- 
Regards,

Laurent Pinchart

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Patch

diff --git a/drivers/media/platform/s3c-camif/camif-capture.c b/drivers/media/platform/s3c-camif/camif-capture.c
index 437395a61065..9ab8e7ee2e1e 100644
--- a/drivers/media/platform/s3c-camif/camif-capture.c
+++ b/drivers/media/platform/s3c-camif/camif-capture.c
@@ -1256,16 +1256,17 @@  static void __camif_subdev_try_format(struct camif_dev *camif,
 {
 	const struct s3c_camif_variant *variant = camif->variant;
 	const struct vp_pix_limits *pix_lim;
-	int i = ARRAY_SIZE(camif_mbus_formats);
+	unsigned int i;
 
 	/* FIXME: constraints against codec or preview path ? */
 	pix_lim = &variant->vp_pix_limits[VP_CODEC];
 
-	while (i-- >= 0)
+	for (i = 0; i < ARRAY_SIZE(camif_mbus_formats); i++)
 		if (camif_mbus_formats[i] == mf->code)
 			break;
 
-	mf->code = camif_mbus_formats[i];
+	if (i == ARRAY_SIZE(camif_mbus_formats))
+		mf->code = camif_mbus_formats[0];
 
 	if (pad == CAMIF_SD_PAD_SINK) {
 		v4l_bound_align_image(&mf->width, 8, CAMIF_MAX_PIX_WIDTH,