fbdev: tdfxfb: avoid divide-by-zero on FBIOPUT_VSCREENINFO

Much like commit 19f953e ("fbdev: fb_pm2fb: Avoid potential divide
by zero error"), we also need to prevent that same crash from happening
in the udlfb driver as it uses pixclock directly when dividing, which
will crash.

Cc: Helge Deller <[email protected]>
Assisted-by: gregkh_clanker_t1000
Cc: stable <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Helge Deller <[email protected]>

Author: gregkh

drivers/video/fbdev/tdfxfb.c

@@ -497,6 +497,9 @@ static int tdfxfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 		}
 	}
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	if (PICOS2KHZ(var->pixclock) > par->max_pixclock) {
 		DPRINTK("pixclock too high (%ldKHz)\n",
 			PICOS2KHZ(var->pixclock));