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

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.

The following log reveals it:
 divide error: 0000 [#1] PREEMPT SMP KASAN PTI
 RIP: 0010:tridentfb_check_var+0x853/0xe60
 Call Trace:
  <TASK>
  fb_set_var+0x367/0xeb0
  do_fb_ioctl+0x234/0x670
  fb_ioctl+0xdd/0x130
  do_syscall_64+0x3b/0x90

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/drivers/video/fbdev/tridentfb.c b/drivers/video/fbdev/tridentfb.c
index 4d20cb557ff0f6e3f2bf959368828818ad2804c1..319131bd72cffa11a965f69588102012942d40fd 100644 (file)
--- a/drivers/video/fbdev/tridentfb.c
+++ b/drivers/video/fbdev/tridentfb.c
@@ -996,6 +996,9 @@ static int tridentfb_check_var(struct fb_var_screeninfo *var,
        int ramdac = 230000; /* 230MHz for most 3D chips */
        debug("enter\n");
 
+       if (!var->pixclock)
+               return -EINVAL;
+
        /* check color depth */
        if (bpp == 24)
                bpp = var->bits_per_pixel = 32;