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From:   Zheyu Ma <zheyuma97@gmail.com>
To:     deller@gmx.de
Cc:     linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, Zheyu Ma <zheyuma97@gmail.com>
Subject: [PATCH 4/7] video: fbdev: vt8623fb: Error out if 'pixclock' equals zero
Date:   Mon,  4 Apr 2022 16:47:20 +0800
Message-Id: <20220404084723.79089-5-zheyuma97@gmail.com>
In-Reply-To: <20220404084723.79089-1-zheyuma97@gmail.com>
References: <20220404084723.79089-1-zheyuma97@gmail.com>
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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 in the function
vt8623fb_check_var().

The following log reveals it:

[   47.778727] divide error: 0000 [#1] PREEMPT SMP KASAN PTI
[   47.778803] RIP: 0010:vt8623fb_set_par+0xecd/0x2210
[   47.778870] Call Trace:
[   47.778872]  <TASK>
[   47.778909]  fb_set_var+0x604/0xeb0
[   47.778995]  do_fb_ioctl+0x234/0x670
[   47.779041]  fb_ioctl+0xdd/0x130
[   47.779048]  do_syscall_64+0x3b/0x90

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/video/fbdev/vt8623fb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/vt8623fb.c b/drivers/video/fbdev/vt8623fb.c
index 7a959e5ba90b..a92a8c670cf0 100644
--- a/drivers/video/fbdev/vt8623fb.c
+++ b/drivers/video/fbdev/vt8623fb.c
@@ -321,6 +321,9 @@ static int vt8623fb_check_var(struct fb_var_screeninfo *var, struct fb_info *inf
 {
 	int rv, mem, step;
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	/* Find appropriate format */
 	rv = svga_match_format (vt8623fb_formats, var, NULL);
 	if (rv < 0)
-- 
2.25.1