wifi: mwifiex: bound uAP association event IEs to the event buffer

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

wifi: mwifiex: bound uAP association event IEs to the event buffer

mwifiex_process_uap_event() handles EVENT_UAP_STA_ASSOC by exposing the
(re)association request IEs that the firmware copies into the event:

sinfo->assoc_req_ies = &event->data[len];
len = (u8 *)sinfo->assoc_req_ies - (u8 *)&event->frame_control;
sinfo->assoc_req_ies_len = le16_to_cpu(event->len) - (u16)len;

event->len is supplied by the device firmware and is never validated,
and the subtraction is unchecked. assoc_req_ies points into
adapter->event_body[MAX_EVENT_SIZE], a fixed-size array embedded in the
kmalloc()'d struct mwifiex_adapter.

On the ap_11n_enabled path mwifiex_set_sta_ht_cap() walks these IEs with
cfg80211_find_ie(), whose for_each_element() loop dereferences each
element header. A firmware-reported event->len larger than the bytes
actually received makes assoc_req_ies_len describe IEs that extend past
event_body, so the walk reads out of the adapter slab object, a
slab-out-of-bounds read (KASAN: slab-out-of-bounds in cfg80211_find_ie).
An event->len smaller than the header instead makes the int subtraction
negative, which wraps to a huge size_t when stored in assoc_req_ies_len.
The same length is handed to cfg80211_new_sta(), so a more modest
over-claim can also copy stale event_body bytes into the
NL80211_CMD_NEW_STATION notification.

A malicious or malfunctioning mwifiex device (USB/SDIO/PCIe) can deliver
such an event while the interface is in AP/uAP mode.

Validate event->len before use: reject a length that underflows the
header or that would place the IEs outside the event_body[] buffer the
event was copied into. event->len here is struct mwifiex_assoc_event.len,
a payload field internal to this event, not the transport frame length,
so it is validated in this handler rather than at the generic
MWIFIEX_TYPE_EVENT receive path, which only sees the event cause and the
transport frame length. The bound is against event_body[MAX_EVENT_SIZE]
rather than the actually-received length because the transports store the
event differently (USB and SDIO leave the 4-byte event header in
event_skb, PCIe strips it via skb_pull), whereas event_body is the single
fixed buffer all of them copy the event into. This is the event-path
analogue of the receive-path bounds checks added in commit 119585281617
("wifi: mwifiex: Fix OOB and integer underflow when rx packets").