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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org,
	stable@vger.kernel.org
Cc: Roman Smirnov <r.smirnov@omp.ru>,
	Sergey Shtylyov <s.shtylyov@omp.ru>,
	Helge Deller <deller@gmx.de>,
	Sasha Levin <sashal@kernel.org>,
	daniel@ffwll.ch,
	linux-fbdev@vger.kernel.org,
	dri-devel@lists.freedesktop.org
Subject: [PATCH AUTOSEL 6.8 25/28] fbmon: prevent division by zero in fb_videomode_from_videomode()
Date: Wed,  3 Apr 2024 13:16:27 -0400
Message-ID: <20240403171656.335224-25-sashal@kernel.org>
In-Reply-To: <20240403171656.335224-1-sashal@kernel.org>
References: <20240403171656.335224-1-sashal@kernel.org>
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From: Roman Smirnov <r.smirnov@omp.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@omp.ru>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.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 79e5bfbdd34c2..0a26399dbc899 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, total;
 
 	fbmode->xres = vm->hactive;
 	fbmode->left_margin = vm->hback_porch;
@@ -1344,8 +1344,9 @@ 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