linux-kernel - [PATCH 5/7] video: fbdev: tridentfb: Error out if 'pixclock' equals zero

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Date:   Mon,  4 Apr 2022 16:47:21 +0800
From:   Zheyu Ma <zheyuma97@...il.com>
To:     deller@....de
Cc:     linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Zheyu Ma <zheyuma97@...il.com>
Subject: [PATCH 5/7] video: fbdev: tridentfb: Error out if 'pixclock' equals zero

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 error.

Fix this by checking whether 'pixclock' is zero.

The following log reveals it:

[   38.260715] divide error: 0000 [#1] PREEMPT SMP KASAN PTI
[   38.260733] RIP: 0010:tridentfb_check_var+0x853/0xe60
[   38.260791] Call Trace:
[   38.260793]  <TASK>
[   38.260796]  fb_set_var+0x367/0xeb0
[   38.260879]  do_fb_ioctl+0x234/0x670
[   38.260922]  fb_ioctl+0xdd/0x130
[   38.260930]  do_syscall_64+0x3b/0x90

Signed-off-by: Zheyu Ma <zheyuma97@...il.com>
---
 drivers/video/fbdev/tridentfb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/tridentfb.c b/drivers/video/fbdev/tridentfb.c
index 4d20cb557ff0..319131bd72cf 100644
--- a/drivers/video/fbdev/tridentfb.c
+++ b/drivers/video/fbdev/tridentfb.c
@@ -996,6 +996,9 @@ static int tridentfb_check_var(struct fb_var_screeninfo *var,
 	int ramdac = 230000; /* 230MHz for most 3D chips */
 	debug("enter\n");
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	/* check color depth */
 	if (bpp == 24)
 		bpp = var->bits_per_pixel = 32;
-- 
2.25.1