linux-kernel - [PATCH AUTOSEL 4.19 4/9] fbdev: tgafb: Fix potential divide by zero

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Message-Id: <20230322200309.1997651-4-sashal@kernel.org>
Date:   Wed, 22 Mar 2023 16:03:04 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Wei Chen <harperchen1110@...il.com>, Helge Deller <deller@....de>,
        Sasha Levin <sashal@...nel.org>, tzimmermann@...e.de,
        javierm@...hat.com, wsa+renesas@...g-engineering.com,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 4.19 4/9] fbdev: tgafb: Fix potential divide by zero

From: Wei Chen <harperchen1110@...il.com>

[ Upstream commit f90bd245de82c095187d8c2cabb8b488a39eaecc ]

fb_set_var would by called when user invokes ioctl with cmd
FBIOPUT_VSCREENINFO. User-provided data would finally reach
tgafb_check_var. In case var->pixclock is assigned to zero,
divide by zero would occur when checking whether reciprocal
of var->pixclock is too high.

Similar crashes have happened in other fbdev drivers. There
is no check and modification on var->pixclock along the call
chain to tgafb_check_var. We believe it could also be triggered
in driver tgafb from user site.

Signed-off-by: Wei Chen <harperchen1110@...il.com>
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/video/fbdev/tgafb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/tgafb.c b/drivers/video/fbdev/tgafb.c
index 65ba9921506e2..9d2912947eef6 100644
--- a/drivers/video/fbdev/tgafb.c
+++ b/drivers/video/fbdev/tgafb.c
@@ -166,6 +166,9 @@ tgafb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 {
 	struct tga_par *par = (struct tga_par *)info->par;
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	if (par->tga_type == TGA_TYPE_8PLANE) {
 		if (var->bits_per_pixel != 8)
 			return -EINVAL;
-- 
2.39.2