CVE-2021-47383 Information

Description

In the Linux kernel the following vulnerability has been resolved:

tty: Fix out-of-bound vmalloc access in imageblit

This issue happens when a userspace program does an ioctl FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct containing only the fields xres yres and bits_per_pixel with values.

If this struct is the same as the previous ioctl the vc_resize() detects it and doesn’t call the resize_screen() leaving the fb_var_screeninfo incomplete. And this leads to the updatescrollmode() calculates a wrong value to fbcon_display->vrows which makes the real_y() return a wrong value of y and that value eventually causes the imageblit to access an out-of-bound address value.

To solve this issue I made the resize_screen() be called even if the screen does not need any resizing so it will ix and fill\ the fb_var_screeninfo independently.

Reference

https://git.kernel.org/stable/c/7e71fcedfda6f7de18f850a6b36e78d78b04476f https://git.kernel.org/stable/c/70aed03b1d5a5df974f456cdc8eedb213c94bb8b https://git.kernel.org/stable/c/067c694d06040db6f0c65281bb358452ca6d85b9 https://git.kernel.org/stable/c/8a6a240f52e14356386030d8958ae8b1761d2325 https://git.kernel.org/stable/c/883f7897a25e3ce14a7f274ca4c73f49ac84002a https://git.kernel.org/stable/c/d570c48dd37dbe8fc6875d4461d01a9554ae2560 https://git.kernel.org/stable/c/699d926585daa6ec44be556cdc1ab89e5d54557b https://git.kernel.org/stable/c/3b0c406124719b625b1aba431659f5cdc24a982c