Subject: CVE-2021-47444: drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read

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

Description
===========

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

drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read

In commit e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid
corruption test") the function connector_bad_edid() started assuming
that the memory for the EDID passed to it was big enough to hold
`edid[0x7e] + 1` blocks of data (1 extra for the base block). It
completely ignored the fact that the function was passed `num_blocks`
which indicated how much memory had been allocated for the EDID.

Let's fix this by adding a bounds check.

This is important for handling the case where there's an error in the
first block of the EDID. In that case we will call
connector_bad_edid() without having re-allocated memory based on
`edid[0x7e]`.

The Linux kernel CVE team has assigned CVE-2021-47444 to this issue.

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

	Issue introduced in 5.7 with commit e11f5bd8228f and fixed in 5.10.75 with commit a7b45024f66f
	Issue introduced in 5.7 with commit e11f5bd8228f and fixed in 5.14.14 with commit 09f3946bb452
	Issue introduced in 5.7 with commit e11f5bd8228f and fixed in 5.15 with commit 97794170b696

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-2021-47444
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/gpu/drm/drm_edid.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/a7b45024f66f9ec769e8dbb1a51ae83cd05929c7
	https://git.kernel.org/stable/c/09f3946bb452918dbfb1982add56f9ffaae393dc
	https://git.kernel.org/stable/c/97794170b696856483f74b47bfb6049780d2d3a0