[PATCH] Fix Bug #11231: gspca_zc3xx oops - 2.6.27-rc1

["Parag Warudkar" <parag.warudkar@gmail.com>]

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[Resend - previous one bounced from vger due to HTML ]

This patch fixes couple of NULL pointer dereferences in zc3xx .
Without this patch my machine oopses as soon as I open Kopete-kde4 .
Patch tested to work fine (no detectable differences in image rendered
by camera - as crappy as ever, no more oopses ;) on x86 with a
Creative Webcam Notebook.

OOPS Analysis
-------------------
http://marc.info/?l=linux-kernel&m=121769418920774&w=4

4575.306109] Code: 83 ec 04 0f b6 90 da 07 00 00 8b a8 04 02 00 00 0f
b6 80 d9 07 00 00 8b 3c 95 f4 dc 15 f9 8b 14 95 d8 dc 15 f9 83 c0 80
89 14 24 <0f> b6 37 0f af f0 8d b6 00 00 00 00 0f b6 83 00 dc 15 f9 0f
af
[ 4575.306133] EIP: [<f915c2d4>] setcontrast+0x34/0xf0 [gspca_zc3xx]
SS:ESP 0068:da81bd64

Which corresponds to -

1374: 0f b6 37 movzbl (%edi),%esi
--^^-- Faulting instruction
1377: 0f af f0 imul %eax,%esi
137a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi

That is this code in zc3xx.c -
k = (sd->contrast - 128) /* -128 / 128 */
                    * Tgamma[0];

Where Tgamma = gamma_tb[sd->gamma];

For sd->gamma=0 Tgamma is NULL -

static const __u8 *gamma_tb[] = {
NULL, ...

Kopete seems to trigger the zero gamma on ioctl and we happily oops in
that case .
Fix this by detecting the zero gamma case while trying to preserve
intended effect of zero gamma .
On reviewing the code, the exact same problem exists for Tgradient
where it is dereferenced when NULL. Fix that too.

Patch also attached.

Signed-off-by: Parag Warudkar <parag.warudkar@gmail.com>

--- linux-2.6/drivers/media/video/gspca/zc3xx.c	2008-07-29
23:26:21.000000000 -0400
+++ linux-2.6-wk/drivers/media/video/gspca/zc3xx.c	2008-08-03
02:17:29.000000000 -0400
@@ -6476,12 +6476,15 @@
 	Tgamma = gamma_tb[sd->gamma];
 	Tgradient = gradient_tb[sd->gamma];

-	k = (sd->contrast - 128)		/* -128 / 128 */
+	if(!Tgamma)
+		k = 0;
+	else
+		k = (sd->contrast - 128)		/* -128 / 128 */
 			* Tgamma[0];
 	PDEBUG(D_CONF, "gamma:%d contrast:%d gamma coeff: %d/128",
 		sd->gamma, sd->contrast, k);
 	for (i = 0; i < 16; i++) {
-		g = Tgamma[i] + kgamma_tb[i] * k / 128;
+		g = (Tgamma ? Tgamma[i] : 0) + kgamma_tb[i] * k / 128;
 		if (g > 0xff)
 			g = 0xff;
 		else if (g <= 0)
@@ -6497,7 +6500,7 @@
 	PDEBUG(D_CONF, "    %02x %02x %02x %02x %02x %02x %02x %02x",
 		v[8], v[9], v[10], v[11], v[12], v[13], v[14], v[15]);
 	for (i = 0; i < 16; i++) {
-		g = Tgradient[i] - kgrad_tb[i] * k / 128;
+		g = (Tgradient ? Tgradient[i] : 0) - kgrad_tb[i] * k / 128;
 		if (g > 0xff)
 			g = 0xff;
 		else if (g <= 0) {

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--- linux-2.6/drivers/media/video/gspca/zc3xx.c	2008-07-29 23:26:21.000000000 -0400
+++ linux-2.6-wk/drivers/media/video/gspca/zc3xx.c	2008-08-03 02:17:29.000000000 -0400
@@ -6476,12 +6476,15 @@
 	Tgamma = gamma_tb[sd->gamma];
 	Tgradient = gradient_tb[sd->gamma];
 
-	k = (sd->contrast - 128)		/* -128 / 128 */
+	if(!Tgamma)
+		k = 0;
+	else
+		k = (sd->contrast - 128)		/* -128 / 128 */
 			* Tgamma[0];
 	PDEBUG(D_CONF, "gamma:%d contrast:%d gamma coeff: %d/128",
 		sd->gamma, sd->contrast, k);
 	for (i = 0; i < 16; i++) {
-		g = Tgamma[i] + kgamma_tb[i] * k / 128;
+		g = (Tgamma ? Tgamma[i] : 0) + kgamma_tb[i] * k / 128;
 		if (g > 0xff)
 			g = 0xff;
 		else if (g <= 0)
@@ -6497,7 +6500,7 @@
 	PDEBUG(D_CONF, "    %02x %02x %02x %02x %02x %02x %02x %02x",
 		v[8], v[9], v[10], v[11], v[12], v[13], v[14], v[15]);
 	for (i = 0; i < 16; i++) {
-		g = Tgradient[i] - kgrad_tb[i] * k / 128;
+		g = (Tgradient ? Tgradient[i] : 0) - kgrad_tb[i] * k / 128;
 		if (g > 0xff)
 			g = 0xff;
 		else if (g <= 0) {