linux-kernel - [PATCH v2] fbmon: prevent division by zero in fb_videomode_from

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Date: Tue, 5 Mar 2024 16:51:50 +0300
From: Roman Smirnov <r.smirnov@....ru>
To: Daniel Vetter <daniel@...ll.ch>, Helge Deller <deller@....de>
CC: Roman Smirnov <r.smirnov@....ru>, Thomas Zimmermann <tzimmermann@...e.de>,
	Sergey Shtylyov <s.shtylyov@....ru>, Karina Yankevich <k.yankevich@....ru>,
	<linux-fbdev@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
	<linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>
Subject: [PATCH v2] fbmon: prevent division by zero in fb_videomode_from_videomode()

The expression htotal * vtotal can have a zero value on
overflow. It is necessary to prevent division by zero like in
fb_var_to_videomode().

Found by Linux Verification Center (linuxtesting.org) with Svace.

Signed-off-by: Roman Smirnov <r.smirnov@....ru>
Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>
---
 V1 -> V2: Replaced the code of the first version with a check.

 drivers/video/fbdev/core/fbmon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
index 79e5bfbdd34c..b137590386da 100644
--- a/drivers/video/fbdev/core/fbmon.c
+++ b/drivers/video/fbdev/core/fbmon.c
@@ -1344,7 +1344,7 @@ int fb_videomode_from_videomode(const struct videomode *vm,
 	vtotal = vm->vactive + vm->vfront_porch + vm->vback_porch +
 		 vm->vsync_len;
 	/* prevent division by zero */
-	if (htotal && vtotal) {
+	if (htotal && vtotal && (vm->pixelclock / htotal >= vtotal)) {
 		fbmode->refresh = vm->pixelclock / (htotal * vtotal);
 	/* a mode must have htotal and vtotal != 0 or it is invalid */
 	} else {
-- 
2.34.1