fbdev: sis: 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-by-zero error.

In sisfb_check_var(), var->pixclock is used as a divisor to caculate
drate before it is checked against zero. Fix this by checking it
at the beginning.

This is similar to CVE-2022-3061 in i740fb which was fixed by
commit 15cf0b8.

Signed-off-by: Fullway Wang <fullwaywang@outlook.com>
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/drivers/video/fbdev/sis/sis_main.c b/drivers/video/fbdev/sis/sis_main.c
index 803ccb6aa479703bc1cb88237b4c3adc594a75a2..009bf1d926448011292c182e7eee29c25930ed6d 100644 (file)
--- a/drivers/video/fbdev/sis/sis_main.c
+++ b/drivers/video/fbdev/sis/sis_main.c
@@ -1444,6 +1444,8 @@ sisfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 
        vtotal = var->upper_margin + var->lower_margin + var->vsync_len;
 
+       if (!var->pixclock)
+               return -EINVAL;
        pixclock = var->pixclock;
 
        if((var->vmode & FB_VMODE_MASK) == FB_VMODE_NONINTERLACED) {