linux-kernel - [PATCH AUTOSEL 6.6 04/21] fbdev: sis: Error out if pixclock equals zero

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Date: Fri,  2 Feb 2024 13:39:51 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Fullway Wang <fullwaywang@...look.com>,
	Helge Deller <deller@....de>,
	Sasha Levin <sashal@...nel.org>,
	tzimmermann@...e.de,
	sam@...nborg.org,
	javierm@...hat.com,
	linux-fbdev@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 6.6 04/21] fbdev: sis: Error out if pixclock equals zero

From: Fullway Wang <fullwaywang@...look.com>

[ Upstream commit e421946be7d9bf545147bea8419ef8239cb7ca52 ]

The userspace program could pass any values to the driver through
ioctl() interface. If the driver doesn't check the value of pixclock,
it may cause divide-by-zero error.

In sisfb_check_var(), var->pixclock is used as a divisor to caculate
drate before it is checked against zero. Fix this by checking it
at the beginning.

This is similar to CVE-2022-3061 in i740fb which was fixed by
commit 15cf0b8.

Signed-off-by: Fullway Wang <fullwaywang@...look.com>
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/video/fbdev/sis/sis_main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/sis/sis_main.c b/drivers/video/fbdev/sis/sis_main.c
index 0f5374f6ef05..6d524a65af18 100644
--- a/drivers/video/fbdev/sis/sis_main.c
+++ b/drivers/video/fbdev/sis/sis_main.c
@@ -1475,6 +1475,8 @@ sisfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 
 	vtotal = var->upper_margin + var->lower_margin + var->vsync_len;
 
+	if (!var->pixclock)
+		return -EINVAL;
 	pixclock = var->pixclock;
 
 	if((var->vmode & FB_VMODE_MASK) == FB_VMODE_NONINTERLACED) {
-- 
2.43.0