CVE-2022-49978

In the Linux kernel, the following vulnerability has been resolved:

fbdev: fb_pm2fb: Avoid potential divide by zero error

In do_fb_ioctl() of fbmem.c, if cmd is FBIOPUT_VSCREENINFO, var will be copied from user, then go through fb_set_var() and info->fbops->fb_check_var() which could may be pm2fb_check_var(). Along the path, var->pixclock won't be modified. This function checks whether reciprocal of var->pixclock is too high. If var->pixclock is zero, there will be a divide by zero error. So, it is necessary to check whether denominator is zero to avoid crash. As this bug is found by Syzkaller, logs are listed below.

divide error in pm2fbcheckvar Call Trace: <TASK> fbsetvar+0x367/0xeb0 drivers/video/fbdev/core/fbmem.c:1015 dofbioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1110 fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1189