wifi: mac80211: add HT and VHT basic set verification

So far we did not verify the HT and VHT basic MCS set. However, in
P802.11REVme/D7.0 (6.5.4.2.4) says that the MLME-JOIN.request shall
return an error if the VHT and HT basic set requirements are not met.

Given broken APs, apply VHT basic MCS/NSS set checks only in
strict mode.

Signed-off-by: Benjamin Berg <[e-mail]>
Reviewed-by: Johannes Berg <[e-mail]>
Signed-off-by: Miri Korenblit <[e-mail]>
Link: https://patch.msgid.link/20250205110958.e2d8d4095f6b.I66bcf6c2de3b9d3325e4ffd9f573f4cd26ce5685@changeid
Signed-off-by: Johannes Berg <[e-mail]>

net/mac80211/mlme.c

···
 }
 
 static bool
+ieee80211_verify_sta_ht_mcs_support(struct ieee80211_sub_if_data *sdata,
+				    struct ieee80211_supported_band *sband,
+				    const struct ieee80211_ht_operation *ht_op)
+{
+	struct ieee80211_sta_ht_cap sta_ht_cap;
+	int i;
+
+	if (sband->band == NL80211_BAND_6GHZ)
+		return true;
+
+	if (!ht_op)
+		return false;
+
+	memcpy(&sta_ht_cap, &sband->ht_cap, sizeof(sta_ht_cap));
+	ieee80211_apply_htcap_overrides(sdata, &sta_ht_cap);
+
+	/*
+	 * P802.11REVme/D7.0 - 6.5.4.2.4
+	 * ...
+	 * If the MLME of an HT STA receives an MLME-JOIN.request primitive
+	 * with the SelectedBSS parameter containing a Basic HT-MCS Set field
+	 * in the HT Operation parameter that contains any unsupported MCSs,
+	 * the MLME response in the resulting MLME-JOIN.confirm primitive shall
+	 * contain a ResultCode parameter that is not set to the value SUCCESS.
+	 * ...
+	 */
+
+	/* Simply check that all basic rates are in the STA RX mask */
+	for (i = 0; i < IEEE80211_HT_MCS_MASK_LEN; i++) {
+		if ((ht_op->basic_set[i] & sta_ht_cap.mcs.rx_mask[i]) !=
+		    ht_op->basic_set[i])
+			return false;
+	}
+
+	return true;
+}
+
+static bool
+ieee80211_verify_sta_vht_mcs_support(struct ieee80211_sub_if_data *sdata,
+				     int link_id,
+				     struct ieee80211_supported_band *sband,
+				     const struct ieee80211_vht_operation *vht_op)
+{
+	struct ieee80211_sta_vht_cap sta_vht_cap;
+	u16 ap_min_req_set, sta_rx_mcs_map, sta_tx_mcs_map;
+	int nss;
+
+	if (sband->band != NL80211_BAND_5GHZ)
+		return true;
+
+	if (!vht_op)
+		return false;
+
+	memcpy(&sta_vht_cap, &sband->vht_cap, sizeof(sta_vht_cap));
+	ieee80211_apply_vhtcap_overrides(sdata, &sta_vht_cap);
+
+	ap_min_req_set = le16_to_cpu(vht_op->basic_mcs_set);
+	sta_rx_mcs_map = le16_to_cpu(sta_vht_cap.vht_mcs.rx_mcs_map);
+	sta_tx_mcs_map = le16_to_cpu(sta_vht_cap.vht_mcs.tx_mcs_map);
+
+	/*
+	 * Many APs are incorrectly advertising an all-zero value here,
+	 * which really means MCS 0-7 are required for 1-8 streams, but
+	 * they don't really mean it that way.
+	 * Some other APs are incorrectly advertising 3 spatial streams
+	 * with MCS 0-7 are required, but don't really mean it that way
+	 * and we'll connect only with HT, rather than even HE.
+	 * As a result, unfortunately the VHT basic MCS/NSS set cannot
+	 * be used at all, so check it only in strict mode.
+	 */
+	if (!ieee80211_hw_check(&sdata->local->hw, STRICT))
+		return true;
+
+	/*
+	 * P802.11REVme/D7.0 - 6.5.4.2.4
+	 * ...
+	 * If the MLME of a VHT STA receives an MLME-JOIN.request primitive
+	 * with a SelectedBSS parameter containing a Basic VHT-MCS And NSS Set
+	 * field in the VHT Operation parameter that contains any unsupported
+	 * <VHT-MCS, NSS> tuple, the MLME response in the resulting
+	 * MLME-JOIN.confirm primitive shall contain a ResultCode parameter
+	 * that is not set to the value SUCCESS.
+	 * ...
+	 */
+	for (nss = 8; nss > 0; nss--) {
+		u8 ap_op_val = (ap_min_req_set >> (2 * (nss - 1))) & 3;
+		u8 sta_rx_val;
+		u8 sta_tx_val;
+
+		if (ap_op_val == IEEE80211_HE_MCS_NOT_SUPPORTED)
+			continue;
+
+		sta_rx_val = (sta_rx_mcs_map >> (2 * (nss - 1))) & 3;
+		sta_tx_val = (sta_tx_mcs_map >> (2 * (nss - 1))) & 3;
+
+		if (sta_rx_val == IEEE80211_HE_MCS_NOT_SUPPORTED ||
+		    sta_tx_val == IEEE80211_HE_MCS_NOT_SUPPORTED ||
+		    sta_rx_val < ap_op_val || sta_tx_val < ap_op_val) {
+			link_id_info(sdata, link_id,
+				     "Missing mandatory rates for %d Nss, rx %d, tx %d oper %d, disable VHT\n",
+				     nss, sta_rx_val, sta_tx_val, ap_op_val);
+			return false;
+		}
+	}
+
+	return true;
+}
+
+static bool
 ieee80211_verify_peer_he_mcs_support(struct ieee80211_sub_if_data *sdata,
 				     int link_id,
 				     const struct ieee80211_he_cap_elem *he_cap,
···
 	if (chanreq->oper.width != ap_chandef->width || ap_mode != conn->mode)
 		link_id_info(sdata, link_id,
 			     "regulatory prevented using AP config, downgraded\n");
+
+	if (conn->mode >= IEEE80211_CONN_MODE_HT &&
+	    !ieee80211_verify_sta_ht_mcs_support(sdata, sband,
+						 elems->ht_operation)) {
+		conn->mode = IEEE80211_CONN_MODE_LEGACY;
+		conn->bw_limit = IEEE80211_CONN_BW_LIMIT_20;
+		link_id_info(sdata, link_id,
+			     "required MCSes not supported, disabling HT\n");
+	}
+
+	if (conn->mode >= IEEE80211_CONN_MODE_VHT &&
+	    !ieee80211_verify_sta_vht_mcs_support(sdata, link_id, sband,
+						  elems->vht_operation)) {
+		conn->mode = IEEE80211_CONN_MODE_HT;
+		conn->bw_limit = min_t(enum ieee80211_conn_bw_limit,
+				       conn->bw_limit,
+				       IEEE80211_CONN_BW_LIMIT_40);
+		link_id_info(sdata, link_id,
+			     "required MCSes not supported, disabling VHT\n");
+	}
 
 	if (conn->mode >= IEEE80211_CONN_MODE_HE &&
 	    (!ieee80211_verify_peer_he_mcs_support(sdata, link_id,