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

[ Upstream commit b36b242d4b8ea178f7fd038965e3cac7f30c3f09 ]

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 #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>

diff --git a/drivers/video/fbdev/asiliantfb.c b/drivers/video/fbdev/asiliantfb.c
index ea31054a28ca80205c50d6b0a97f7a71fb177297..c1d6e6336225976120dda8622e59a9ff72c89049 100644 (file)
--- a/drivers/video/fbdev/asiliantfb.c
+++ b/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;