mac80211: Allow HE operation to be longer than expected.

We observed some Cisco APs sending the following HE Operation IE in
associate response:

  ff 0a 24 f4 3f 00 01 fc ff 00 00 00

Its HE operation parameter is 0x003ff4, so the expected total length is
7 which does not match the actual length = 10. This causes association
failing with "HE AP is missing HE Capability/operation."

According to P802.11ax_D4 Table9-94, HE operation is extensible, and
according to 802.11-2016 10.27.8, STA should discard the part beyond
the maximum length and parse the truncated element.

Allow HE operation element to be longer than expected to handle this
case and future extensions.

Fixes: e4d005b80d ("mac80211: refactor extended element parsing")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Yen-lin Lai <yenlinlai@chromium.org>
Link: https://lore.kernel.org/r/20210223051926.2653301-1-yenlinlai@chromium.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mlme.c

@@ -5071,7 +5071,7 @@ static int ieee80211_prep_channel(struct ieee80211_sub_if_data *sdata,
 		he_oper_ie = cfg80211_find_ext_ie(WLAN_EID_EXT_HE_OPERATION,
 						  ies->data, ies->len);
 		if (he_oper_ie &&
-		    he_oper_ie[1] == ieee80211_he_oper_size(&he_oper_ie[3]))
+		    he_oper_ie[1] >= ieee80211_he_oper_size(&he_oper_ie[3]))
 			he_oper = (void *)(he_oper_ie + 3);
 		else
 			he_oper = NULL;

net/mac80211/util.c

@@ -968,7 +968,7 @@ static void ieee80211_parse_extension_element(u32 *crc,
 		break;
 	case WLAN_EID_EXT_HE_OPERATION:
 		if (len >= sizeof(*elems->he_operation) &&
-		    len == ieee80211_he_oper_size(data) - 1) {
+		    len >= ieee80211_he_oper_size(data) - 1) {
 			if (crc)
 				*crc = crc32_be(*crc, (void *)elem,
 						elem->datalen + 2);