linux-kernel - [PATCH] fbdev: tgafb: Fix potential divide by zero

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Message-Id: <20230307130856.2295182-1-harperchen1110@gmail.com>
Date:   Tue,  7 Mar 2023 13:08:56 +0000
From:   harperchen <harperchen1110@...il.com>
To:     deller@....de
Cc:     javierm@...hat.com, tzimmermann@...e.de,
        wsa+renesas@...g-engineering.com, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        harperchen <harperchen1110@...il.com>
Subject: [PATCH] fbdev: tgafb: Fix potential divide by zero

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: harperchen <harperchen1110@...il.com>
---
 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 14d37c49633c..b44004880f0d 100644
--- a/drivers/video/fbdev/tgafb.c
+++ b/drivers/video/fbdev/tgafb.c
@@ -173,6 +173,9 @@ 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;
-- 
2.25.1