Re: [patch] fbdev: off by one test (harmless)

On 15/01/15 14:43, Dan Carpenter wrote:

Sounds good to me.  :)  Could I get a Reported-by cookie?

Oh, sorry. I thought I had added that, but... seems I didn't. Well now it's
there. So updated patch below.

I'll queue it for 3.20 if there are no comments.

 Tomi


From 80fa3aed6f89728e9003bb0bdbd0b4bac2bc2186 Mon Sep 17 00:00:00 2001
From: Tomi Valkeinen <redacted>
Date: Thu, 15 Jan 2015 13:47:19 +0200
Subject: [PATCH] fbdev: fix cea_modes array size

CEA defines 64 modes, indexed from 1 to 64. modedb has cea_modes arrays,
which contains 64 entries. However, the code uses the CEA indices
directly, i.e. the first mode is at cea_modes[1]. This means the array
is one too short.

This does not cause references to uninitialized memory as the code in
fbmon only allows indexes up to 63, and the cea_modes does not contain
an entry for the mode 64 so it could not be used in any case.

However, the code contains a check 'if (idx > ARRAY_SIZE(cea_modes)',
and while that check is a no-op as at that point idx cannot be >= 63, it
upsets static checkers.

Fix this by increasing the cea_array size to be 65, and change the code
to allow mode 64.

Signed-off-by: Tomi Valkeinen <redacted>
Reported-by: Dan Carpenter <redacted>
---
 drivers/video/fbdev/core/fbmon.c  | 4 ++--
 drivers/video/fbdev/core/modedb.c | 2 +-
 include/linux/fb.h                | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
index 5b0e313849bd..1829fe34a1df 100644
--- a/drivers/video/fbdev/core/fbmon.c
+++ b/drivers/video/fbdev/core/fbmon.c

@@ -1059,9 +1059,9 @@ void fb_edid_add_monspecs(unsigned char *edid, struct fb_monspecs *specs)
 
 	for (i = specs->modedb_len + num; i < specs->modedb_len + num + svd_n; i++) {
 		int idx = svd[i - specs->modedb_len - num];
-		if (!idx || idx > 63) {
+		if (!idx || idx >= ARRAY_SIZE(cea_modes)) {
 			pr_warning("Reserved SVD code %d\n", idx);
-		} else if (idx > ARRAY_SIZE(cea_modes) || !cea_modes[idx].xres) {
+		} else if (!cea_modes[idx].xres) {
 			pr_warning("Unimplemented SVD code %d\n", idx);
 		} else {
 			memcpy(&m[i], cea_modes + idx, sizeof(m[i]));

diff --git a/drivers/video/fbdev/core/modedb.c b/drivers/video/fbdev/core/modedb.c
index 388f7971494b..b2aba4e3150a 100644
--- a/drivers/video/fbdev/core/modedb.c
+++ b/drivers/video/fbdev/core/modedb.c

@@ -289,7 +289,7 @@ static const struct fb_videomode modedb[] = {
 };
 
 #ifdef CONFIG_FB_MODE_HELPERS
-const struct fb_videomode cea_modes[64] = {
+const struct fb_videomode cea_modes[65] = {
 	/* #1: 640x480p@59.94/60Hz */
 	[1] = {
 		NULL, 60, 640, 480, 39722, 48, 16, 33, 10, 96, 2, 0,

diff --git a/include/linux/fb.h b/include/linux/fb.h
index 09bb7a18d287..024260687698 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h

@@ -779,7 +779,7 @@ struct fb_videomode {
 
 extern const char *fb_mode_option;
 extern const struct fb_videomode vesa_modes[];
-extern const struct fb_videomode cea_modes[64];
+extern const struct fb_videomode cea_modes[65];
 
 struct fb_modelist {
 	struct list_head list;

-- 
2.2.2