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

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Date: Tue, 5 Mar 2024 11:20:40 +0300
From: Roman Smirnov <r.smirnov@....ru>
To: Daniel Vetter <daniel@...ll.ch>, Helge Deller <deller@....de>
CC: Roman Smirnov <r.smirnov@....ru>, 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] 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>
---
 drivers/video/fbdev/core/fbmon.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
index 79e5bfbdd34c..bd98b138da6a 100644
--- a/drivers/video/fbdev/core/fbmon.c
+++ b/drivers/video/fbdev/core/fbmon.c
@@ -1311,7 +1311,7 @@ int fb_get_mode(int flags, u32 val, struct fb_var_screeninfo *var, struct fb_inf
 int fb_videomode_from_videomode(const struct videomode *vm,
 				struct fb_videomode *fbmode)
 {
-	unsigned int htotal, vtotal;
+	unsigned int htotal, vtotal, hfreq;
 
 	fbmode->xres = vm->hactive;
 	fbmode->left_margin = vm->hback_porch;
@@ -1345,7 +1345,8 @@ int fb_videomode_from_videomode(const struct videomode *vm,
 		 vm->vsync_len;
 	/* prevent division by zero */
 	if (htotal && vtotal) {
-		fbmode->refresh = vm->pixelclock / (htotal * vtotal);
+		hfreq = vm->pixelclock / htotal;
+		fbmode->refresh = hfreq / vtotal;
 	/* a mode must have htotal and vtotal != 0 or it is invalid */
 	} else {
 		fbmode->refresh = 0;
-- 
2.34.1