[PATCH 1/3] video: fbdev: kyro: add a check against divide error

[Zheyu Ma]

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 because the value of 'lineclock' and
'frameclock' will be zero.

Fix this by checking whether 'pixclock' is zero in kyrofb_check_var().

The following log reveals it:

[  103.073930] divide error: 0000 [#1] PREEMPT SMP KASAN PTI
[  103.073942] CPU: 4 PID: 12483 Comm: syz-executor Not tainted 5.14.0-rc2-00478-g2734d6c1b1a0-dirty #118
[  103.073959] RIP: 0010:kyrofb_set_par+0x316/0xc80
[  103.074045] Call Trace:
[  103.074048]  ? ___might_sleep+0x1ee/0x2d0
[  103.074060]  ? kyrofb_ioctl+0x330/0x330
[  103.074069]  fb_set_var+0x5bf/0xeb0
[  103.074078]  ? fb_blank+0x1a0/0x1a0
[  103.074085]  ? lock_acquire+0x3bd/0x530
[  103.074094]  ? lock_release+0x810/0x810
[  103.074103]  ? ___might_sleep+0x1ee/0x2d0
[  103.074114]  ? __mutex_lock+0x620/0x1190
[  103.074126]  ? trace_hardirqs_on+0x6a/0x1c0
[  103.074137]  do_fb_ioctl+0x31e/0x700
[  103.074144]  ? fb_getput_cmap+0x280/0x280
[  103.074152]  ? rcu_read_lock_sched_held+0x11/0x80
[  103.074162]  ? rcu_read_lock_sched_held+0x11/0x80
[  103.074171]  ? __sanitizer_cov_trace_switch+0x67/0xf0
[  103.074181]  ? __sanitizer_cov_trace_const_cmp2+0x20/0x80
[  103.074191]  ? do_vfs_ioctl+0x14b/0x16c0
[  103.074199]  ? vfs_fileattr_set+0xb60/0xb60
[  103.074207]  ? rcu_read_lock_sched_held+0x11/0x80
[  103.074216]  ? lock_release+0x483/0x810
[  103.074224]  ? __fget_files+0x217/0x3d0
[  103.074234]  ? __fget_files+0x239/0x3d0
[  103.074243]  ? do_fb_ioctl+0x700/0x700
[  103.074250]  fb_ioctl+0xe6/0x130

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

diff --git a/drivers/video/fbdev/kyro/fbdev.c b/drivers/video/fbdev/kyro/fbdev.c
index 8fbde92ae8b9..6db7e5e83f11 100644
--- a/drivers/video/fbdev/kyro/fbdev.c
+++ b/drivers/video/fbdev/kyro/fbdev.c
@@ -394,6 +394,9 @@ static int kyrofb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 {
 	struct kyrofb_info *par = info->par;
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	if (var->bits_per_pixel != 16 && var->bits_per_pixel != 32) {
 		printk(KERN_WARNING "kyrofb: depth not supported: %u\n", var->bits_per_pixel);
 		return -EINVAL;
-- 
2.17.6