[PATCH v2] wifi: mwifiex: bound uAP association event IEs to the event buffer

[HE WEI (ギカク)]

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").

Fixes: e568634ae7ac ("mwifiex: add AP event handling framework")
Signed-off-by: HE WEI (ギカク) <skyexpoc@xxxxxxxxx>
---
v2: fold le16_to_cpu(event->len) into a local evt_len as requested, which
    also shortens the bounds check.  No functional change.

 .../net/wireless/marvell/mwifiex/uap_event.c  | 24 +++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/uap_event.c b/drivers/net/wireless/marvell/mwifiex/uap_event.c
index 679fdae0f001..ba1bdbbff687 100644
--- a/drivers/net/wireless/marvell/mwifiex/uap_event.c
+++ b/drivers/net/wireless/marvell/mwifiex/uap_event.c
@@ -123,11 +123,31 @@ int mwifiex_process_uap_event(struct mwifiex_private *priv)
 				len = ETH_ALEN;
 
 			if (len != -1) {
+				u16 evt_len = le16_to_cpu(event->len);
+
 				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 reported by the device firmware
+				 * and is not otherwise validated.  Reject a
+				 * length that underflows the header, or that
+				 * would place the association request IEs
+				 * outside the fixed-size event_body[] buffer the
+				 * event was copied into; otherwise the IE walk
+				 * in mwifiex_set_sta_ht_cap() reads past
+				 * event_body and out of the adapter slab object.
+				 */
+				if (evt_len < len ||
+				    (u8 *)&event->frame_control + evt_len >
+				    adapter->event_body + MAX_EVENT_SIZE) {
+					mwifiex_dbg(adapter, ERROR,
+						    "invalid STA assoc event length\n");
+					kfree(sinfo);
+					return -1;
+				}
+				sinfo->assoc_req_ies_len = evt_len - (u16)len;
 			}
 		}
 		cfg80211_new_sta(priv->netdev->ieee80211_ptr, event->sta_addr,
-- 
2.54.0