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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 7/7] video: fbdev: s3fb: Error out if 'pixclock' equals zero
Date:   Mon,  4 Apr 2022 16:47:23 +0800
Message-Id: <20220404084723.79089-8-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 s3fb_check_var().

The following log reveals it:

[  511.141561] divide error: 0000 [#1] PREEMPT SMP KASAN PTI
[  511.141607] RIP: 0010:s3fb_check_var+0x3f3/0x530
[  511.141693] Call Trace:
[  511.141695]  <TASK>
[  511.141716]  fb_set_var+0x367/0xeb0
[  511.141815]  do_fb_ioctl+0x234/0x670
[  511.141876]  fb_ioctl+0xdd/0x130
[  511.141888]  do_syscall_64+0x3b/0x90

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/video/fbdev/s3fb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/s3fb.c b/drivers/video/fbdev/s3fb.c
index 5c74253e7b2c..b93c8eb02336 100644
--- a/drivers/video/fbdev/s3fb.c
+++ b/drivers/video/fbdev/s3fb.c
@@ -549,6 +549,9 @@ static int s3fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 	int rv, mem, step;
 	u16 m, n, r;
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	/* Find appropriate format */
 	rv = svga_match_format (s3fb_formats, var, NULL);
 
-- 
2.25.1