Subject: CVE-2021-46980: usb: typec: ucsi: Retrieve all the PDOs instead of just the first 4

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

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

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

usb: typec: ucsi: Retrieve all the PDOs instead of just the first 4

commit 4dbc6a4ef06d ("usb: typec: ucsi: save power data objects
in PD mode") introduced retrieval of the PDOs when connected to a
PD-capable source. But only the first 4 PDOs are received since
that is the maximum number that can be fetched at a time given the
MESSAGE_IN length limitation (16 bytes). However, as per the PD spec
a connected source may advertise up to a maximum of 7 PDOs.

If such a source is connected it's possible the PPM could have
negotiated a power contract with one of the PDOs at index greater
than 4, and would be reflected in the request data object's (RDO)
object position field. This would result in an out-of-bounds access
when the rdo_index() is used to index into the src_pdos array in
ucsi_psy_get_voltage_now().

With the help of the UBSAN -fsanitize=array-bounds checker enabled
this exact issue is revealed when connecting to a PD source adapter
that advertise 5 PDOs and the PPM enters a contract having selected
the 5th one.

[  151.545106][   T70] Unexpected kernel BRK exception at EL1
[  151.545112][   T70] Internal error: BRK handler: f2005512 [#1] PREEMPT SMP
...
[  151.545499][   T70] pc : ucsi_psy_get_prop+0x208/0x20c
[  151.545507][   T70] lr : power_supply_show_property+0xc0/0x328
...
[  151.545542][   T70] Call trace:
[  151.545544][   T70]  ucsi_psy_get_prop+0x208/0x20c
[  151.545546][   T70]  power_supply_uevent+0x1a4/0x2f0
[  151.545550][   T70]  dev_uevent+0x200/0x384
[  151.545555][   T70]  kobject_uevent_env+0x1d4/0x7e8
[  151.545557][   T70]  power_supply_changed_work+0x174/0x31c
[  151.545562][   T70]  process_one_work+0x244/0x6f0
[  151.545564][   T70]  worker_thread+0x3e0/0xa64

We can resolve this by instead retrieving and storing up to the
maximum of 7 PDOs in the con->src_pdos array. This would involve
two calls to the GET_PDOS command.

The Linux kernel CVE team has assigned CVE-2021-46980 to this issue.

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

	Issue introduced in 5.8 with commit 4dbc6a4ef06d and fixed in 5.10.38 with commit e5366bea0277
	Issue introduced in 5.8 with commit 4dbc6a4ef06d and fixed in 5.11.22 with commit a453bfd7ef15
	Issue introduced in 5.8 with commit 4dbc6a4ef06d and fixed in 5.12.5 with commit 5e9c6f58b01e
	Issue introduced in 5.8 with commit 4dbc6a4ef06d and fixed in 5.13 with commit 1f4642b72be7

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-2021-46980
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/usb/typec/ucsi/ucsi.c
	drivers/usb/typec/ucsi/ucsi.h

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/e5366bea0277425e1868ba20eeb27c879d5a6e2d
	https://git.kernel.org/stable/c/a453bfd7ef15fd9d524004d3ca7b05353a302911
	https://git.kernel.org/stable/c/5e9c6f58b01e6fdfbc740390c01f542a35c97e57
	https://git.kernel.org/stable/c/1f4642b72be79757f050924a9b9673b6a02034bc