video: fbdev: asiliantfb: Error out if 'pixclock' equals zero

[ Upstream commit b36b242 ]

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 first.

The following log reveals it:

[   43.861711] divide error: 0000 [#1] PREEMPT SMP KASAN PTI
[   43.861737] CPU: 2 PID: 11764 Comm: i740 Not tainted 5.14.0-rc2-00513-gac532c9bbcfb-dirty torvalds#224
[   43.861756] RIP: 0010:asiliantfb_check_var+0x4e/0x730
[   43.861843] Call Trace:
[   43.861848]  ? asiliantfb_remove+0x190/0x190
[   43.861858]  fb_set_var+0x2e4/0xeb0
[   43.861866]  ? fb_blank+0x1a0/0x1a0
[   43.861873]  ? lock_acquire+0x1ef/0x530
[   43.861884]  ? lock_release+0x810/0x810
[   43.861892]  ? lock_is_held_type+0x100/0x140
[   43.861903]  ? ___might_sleep+0x1ee/0x2d0
[   43.861914]  ? __mutex_lock+0x620/0x1190
[   43.861921]  ? do_fb_ioctl+0x313/0x700
[   43.861929]  ? mutex_lock_io_nested+0xfa0/0xfa0
[   43.861936]  ? __this_cpu_preempt_check+0x1d/0x30
[   43.861944]  ? _raw_spin_unlock_irqrestore+0x46/0x60
[   43.861952]  ? lockdep_hardirqs_on+0x59/0x100
[   43.861959]  ? _raw_spin_unlock_irqrestore+0x46/0x60
[   43.861967]  ? trace_hardirqs_on+0x6a/0x1c0
[   43.861978]  do_fb_ioctl+0x31e/0x700

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1627293835-17441-2-git-send-email-zheyuma97@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/video/fbdev/asiliantfb.c

@@ -227,6 +227,9 @@ static int asiliantfb_check_var(struct fb_var_screeninfo *var,
 {
 	unsigned long Ftarget, ratio, remainder;
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	ratio = 1000000 / var->pixclock;
 	remainder = 1000000 % var->pixclock;
 	Ftarget = 1000000 * ratio + (1000000 * remainder) / var->pixclock;