CVE-2021-46980

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.