linux-kernel - [PATCH 5.10 24/39] video: fbdev: i740fb: Error out if pixclock equals zero

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Date:   Wed, 21 Sep 2022 17:46:29 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Zheyu Ma <zheyuma97@...il.com>,
        Helge Deller <deller@....de>,
        Stefan Ghinea <stefan.ghinea@...driver.com>
Subject: [PATCH 5.10 24/39] video: fbdev: i740fb: Error out if pixclock equals zero

From: Zheyu Ma <zheyuma97@...il.com>

commit 15cf0b82271b1823fb02ab8c377badba614d95d5 upstream.

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
i740fb_check_var().

The following log reveals it:

divide error: 0000 [#1] PREEMPT SMP KASAN PTI
RIP: 0010:i740fb_decode_var drivers/video/fbdev/i740fb.c:444 [inline]
RIP: 0010:i740fb_set_par+0x272f/0x3bb0 drivers/video/fbdev/i740fb.c:739
Call Trace:
    fb_set_var+0x604/0xeb0 drivers/video/fbdev/core/fbmem.c:1036
    do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1112
    fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1191
    vfs_ioctl fs/ioctl.c:51 [inline]
    __do_sys_ioctl fs/ioctl.c:874 [inline]

Signed-off-by: Zheyu Ma <zheyuma97@...il.com>
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Stefan Ghinea <stefan.ghinea@...driver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/video/fbdev/i740fb.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/video/fbdev/i740fb.c
+++ b/drivers/video/fbdev/i740fb.c
@@ -662,6 +662,9 @@ static int i740fb_decode_var(const struc
 
 static int i740fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 {
+	if (!var->pixclock)
+		return -EINVAL;
+
 	switch (var->bits_per_pixel) {
 	case 8:
 		var->red.offset	= var->green.offset = var->blue.offset = 0;