Subject: CVE-2021-47383: tty: Fix out-of-bound vmalloc access in imageblit

From: Greg Kroah-Hartman <[email-masked]>

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
"fix and fill" the fb_var_screeninfo independently.

The Linux kernel CVE team has assigned CVE-2021-47383 to this issue.

Affected and fixed versions
===========================

	Fixed in 4.4.286 with commit 7e71fcedfda6
	Fixed in 4.9.285 with commit 70aed03b1d5a
	Fixed in 4.14.249 with commit 067c694d0604
	Fixed in 4.19.209 with commit 8a6a240f52e1
	Fixed in 5.4.151 with commit 883f7897a25e
	Fixed in 5.10.71 with commit d570c48dd37d
	Fixed in 5.14.10 with commit 699d926585da
	Fixed in 5.15 with commit 3b0c40612471

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47383
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/tty/vt/vt.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	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