linux-kernel - [PATCH AUTOSEL 4.19 5/5] fbmon: prevent division by zero in fb_videomode_from

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Date: Wed,  3 Apr 2024 13:20:38 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Roman Smirnov <r.smirnov@....ru>,
	Sergey Shtylyov <s.shtylyov@....ru>,
	Helge Deller <deller@....de>,
	Sasha Levin <sashal@...nel.org>,
	daniel@...ll.ch,
	linux-fbdev@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 4.19 5/5] fbmon: prevent division by zero in fb_videomode_from_videomode()

From: Roman Smirnov <r.smirnov@....ru>

[ Upstream commit c2d953276b8b27459baed1277a4fdd5dd9bd4126 ]

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>
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/video/fbdev/core/fbmon.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
index 8607439d69328..e4040fb860bbc 100644
--- a/drivers/video/fbdev/core/fbmon.c
+++ b/drivers/video/fbdev/core/fbmon.c
@@ -1309,7 +1309,7 @@ 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, total;
 
 	fbmode->xres = vm->hactive;
 	fbmode->left_margin = vm->hback_porch;
@@ -1342,8 +1342,9 @@ 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) {
-		fbmode->refresh = vm->pixelclock / (htotal * vtotal);
+	total = htotal * vtotal;
+	if (total) {
+		fbmode->refresh = vm->pixelclock / total;
 	/* a mode must have htotal and vtotal != 0 or it is invalid */
 	} else {
 		fbmode->refresh = 0;
-- 
2.43.0