text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * Copyright (c) 2008, 2009 open80211s Ltd.
   * Copyright (C) 2019, 2021 Intel Corporation
   * Author:     Luis Carlos Cobo <luisca@cozybit.com>
   */
  #include <linux/gfp.h>
  #include <linux/kernel.h>
  #include <linux/random.h>
  #include <linux/rculist.h>
  
  #include "ieee80211_i.h"
  #include "rate.h"
  #include "mesh.h"
  
  #define PLINK_CNF_AID(mgmt) ((mgmt)->u.action.u.self_prot.variable + 2)
  #define PLINK_GET_LLID(p) (p + 2)
  #define PLINK_GET_PLID(p) (p + 4)
  
  #define mod_plink_timer(s, t) (mod_timer(&s->mesh->plink_timer, \
  				jiffies + msecs_to_jiffies(t)))
  
  enum plink_event {
  	PLINK_UNDEFINED,
  	OPN_ACPT,
  	OPN_RJCT,
  	OPN_IGNR,
  	CNF_ACPT,
  	CNF_RJCT,
  	CNF_IGNR,
  	CLS_ACPT,
  	CLS_IGNR
  };
  
  static const char * const mplstates[] = {
  	[NL80211_PLINK_LISTEN] = "LISTEN",
  	[NL80211_PLINK_OPN_SNT] = "OPN-SNT",
  	[NL80211_PLINK_OPN_RCVD] = "OPN-RCVD",
  	[NL80211_PLINK_CNF_RCVD] = "CNF_RCVD",
  	[NL80211_PLINK_ESTAB] = "ESTAB",
  	[NL80211_PLINK_HOLDING] = "HOLDING",
  	[NL80211_PLINK_BLOCKED] = "BLOCKED"
  };
  
  static const char * const mplevents[] = {
  	[PLINK_UNDEFINED] = "NONE",
  	[OPN_ACPT] = "OPN_ACPT",
  	[OPN_RJCT] = "OPN_RJCT",
  	[OPN_IGNR] = "OPN_IGNR",
  	[CNF_ACPT] = "CNF_ACPT",
  	[CNF_RJCT] = "CNF_RJCT",
  	[CNF_IGNR] = "CNF_IGNR",
  	[CLS_ACPT] = "CLS_ACPT",
  	[CLS_IGNR] = "CLS_IGNR"
  };
  
  /* We only need a valid sta if user configured a minimum rssi_threshold. */
  static bool rssi_threshold_check(struct ieee80211_sub_if_data *sdata,
  				 struct sta_info *sta)
  {
  	s32 rssi_threshold = sdata->u.mesh.mshcfg.rssi_threshold;
  	return rssi_threshold == 0 ||
  	       (sta &&
  		(s8)-ewma_signal_read(&sta->rx_stats_avg.signal) >
  						rssi_threshold);
  }
  
  /**
   * mesh_plink_fsm_restart - restart a mesh peer link finite state machine
   *
   * @sta: mesh peer link to restart
   *
   * Locking: this function must be called holding sta->mesh->plink_lock
   */
  static inline void mesh_plink_fsm_restart(struct sta_info *sta)
  {
  	lockdep_assert_held(&sta->mesh->plink_lock);
  	sta->mesh->plink_state = NL80211_PLINK_LISTEN;
  	sta->mesh->llid = sta->mesh->plid = sta->mesh->reason = 0;
  	sta->mesh->plink_retries = 0;
  }
  
  /*
   * mesh_set_short_slot_time - enable / disable ERP short slot time.
   *
   * The standard indirectly mandates mesh STAs to turn off short slot time by
   * disallowing advertising this (802.11-2012 8.4.1.4), but that doesn't mean we
   * can't be sneaky about it. Enable short slot time if all mesh STAs in the
   * MBSS support ERP rates.
   *
   * Returns BSS_CHANGED_ERP_SLOT or 0 for no change.
   */
  static u32 mesh_set_short_slot_time(struct ieee80211_sub_if_data *sdata)
  {
  	struct ieee80211_local *local = sdata->local;
  	struct ieee80211_supported_band *sband;
  	struct sta_info *sta;
  	u32 erp_rates = 0, changed = 0;
  	int i;
  	bool short_slot = false;
  
  	sband = ieee80211_get_sband(sdata);
  	if (!sband)
  		return changed;
  
  	if (sband->band == NL80211_BAND_5GHZ) {
  		/* (IEEE 802.11-2012 19.4.5) */
  		short_slot = true;
  		goto out;
  	} else if (sband->band != NL80211_BAND_2GHZ) {
  		goto out;
  	}
  
  	for (i = 0; i < sband->n_bitrates; i++)
  		if (sband->bitrates[i].flags & IEEE80211_RATE_ERP_G)
  			erp_rates |= BIT(i);
  
  	if (!erp_rates)
  		goto out;
  
  	rcu_read_lock();
  	list_for_each_entry_rcu(sta, &local->sta_list, list) {
  		if (sdata != sta->sdata ||
  		    sta->mesh->plink_state != NL80211_PLINK_ESTAB)
  			continue;
  
  		short_slot = false;
  		if (erp_rates & sta->sta.supp_rates[sband->band])
  			short_slot = true;
  		 else
  			break;
  	}
  	rcu_read_unlock();
  
  out:
  	if (sdata->vif.bss_conf.use_short_slot != short_slot) {
  		sdata->vif.bss_conf.use_short_slot = short_slot;
  		changed = BSS_CHANGED_ERP_SLOT;
  		mpl_dbg(sdata, "mesh_plink %pM: ERP short slot time %d\n",
  			sdata->vif.addr, short_slot);
  	}
  	return changed;
  }
  
  /**
   * mesh_set_ht_prot_mode - set correct HT protection mode
   * @sdata: the (mesh) interface to handle
   *
   * Section 9.23.3.5 of IEEE 80211-2012 describes the protection rules for HT
   * mesh STA in a MBSS. Three HT protection modes are supported for now, non-HT
   * mixed mode, 20MHz-protection and no-protection mode. non-HT mixed mode is
   * selected if any non-HT peers are present in our MBSS.  20MHz-protection mode
   * is selected if all peers in our 20/40MHz MBSS support HT and at least one
   * HT20 peer is present. Otherwise no-protection mode is selected.
   */
  static u32 mesh_set_ht_prot_mode(struct ieee80211_sub_if_data *sdata)
  {
  	struct ieee80211_local *local = sdata->local;
  	struct sta_info *sta;
  	u16 ht_opmode;
  	bool non_ht_sta = false, ht20_sta = false;
  
  	switch (sdata->vif.bss_conf.chandef.width) {
  	case NL80211_CHAN_WIDTH_20_NOHT:
  	case NL80211_CHAN_WIDTH_5:
  	case NL80211_CHAN_WIDTH_10:
  		return 0;
  	default:
  		break;
  	}
  
  	rcu_read_lock();
  	list_for_each_entry_rcu(sta, &local->sta_list, list) {
  		if (sdata != sta->sdata ||
  		    sta->mesh->plink_state != NL80211_PLINK_ESTAB)
  			continue;
  
  		if (sta->sta.bandwidth > IEEE80211_STA_RX_BW_20)
  			continue;
  
  		if (!sta->sta.ht_cap.ht_supported) {
  			mpl_dbg(sdata, "nonHT sta (%pM) is present\n",
  				       sta->sta.addr);
  			non_ht_sta = true;
  			break;
  		}
  
  		mpl_dbg(sdata, "HT20 sta (%pM) is present\n", sta->sta.addr);
  		ht20_sta = true;
  	}
  	rcu_read_unlock();
  
  	if (non_ht_sta)
  		ht_opmode = IEEE80211_HT_OP_MODE_PROTECTION_NONHT_MIXED;
  	else if (ht20_sta &&
  		 sdata->vif.bss_conf.chandef.width > NL80211_CHAN_WIDTH_20)
  		ht_opmode = IEEE80211_HT_OP_MODE_PROTECTION_20MHZ;
  	else
  		ht_opmode = IEEE80211_HT_OP_MODE_PROTECTION_NONE;
  
  	if (sdata->vif.bss_conf.ht_operation_mode == ht_opmode)
  		return 0;
  
  	sdata->vif.bss_conf.ht_operation_mode = ht_opmode;
  	sdata->u.mesh.mshcfg.ht_opmode = ht_opmode;
  	mpl_dbg(sdata, "selected new HT protection mode %d\n", ht_opmode);
  	return BSS_CHANGED_HT;
  }
  
  static int mesh_plink_frame_tx(struct ieee80211_sub_if_data *sdata,
  			       struct sta_info *sta,
  			       enum ieee80211_self_protected_actioncode action,
  			       u8 *da, u16 llid, u16 plid, u16 reason)
  {
  	struct ieee80211_local *local = sdata->local;
  	struct sk_buff *skb;
  	struct ieee80211_tx_info *info;
  	struct ieee80211_mgmt *mgmt;
  	bool include_plid = false;
  	u16 peering_proto = 0;
  	u8 *pos, ie_len = 4;
  	u8 ie_len_he_cap;
  	int hdr_len = offsetofend(struct ieee80211_mgmt, u.action.u.self_prot);
  	int err = -ENOMEM;
  
  	ie_len_he_cap = ieee80211_ie_len_he_cap(sdata,
  						NL80211_IFTYPE_MESH_POINT);
  	skb = dev_alloc_skb(local->tx_headroom +
  			    hdr_len +
  			    2 + /* capability info */
  			    2 + /* AID */
  			    2 + 8 + /* supported rates */
  			    2 + (IEEE80211_MAX_SUPP_RATES - 8) +
  			    2 + sdata->u.mesh.mesh_id_len +
  			    2 + sizeof(struct ieee80211_meshconf_ie) +
  			    2 + sizeof(struct ieee80211_ht_cap) +
  			    2 + sizeof(struct ieee80211_ht_operation) +
  			    2 + sizeof(struct ieee80211_vht_cap) +
  			    2 + sizeof(struct ieee80211_vht_operation) +
  			    ie_len_he_cap +
  			    2 + 1 + sizeof(struct ieee80211_he_operation) +
  				    sizeof(struct ieee80211_he_6ghz_oper) +
  			    2 + 1 + sizeof(struct ieee80211_he_6ghz_capa) +
  			    2 + 8 + /* peering IE */
  			    sdata->u.mesh.ie_len);
  	if (!skb)
  		return err;
  	info = IEEE80211_SKB_CB(skb);
  	skb_reserve(skb, local->tx_headroom);
  	mgmt = skb_put_zero(skb, hdr_len);
  	mgmt->frame_control = cpu_to_le16(IEEE80211_FTYPE_MGMT |
  					  IEEE80211_STYPE_ACTION);
  	memcpy(mgmt->da, da, ETH_ALEN);
  	memcpy(mgmt->sa, sdata->vif.addr, ETH_ALEN);
  	memcpy(mgmt->bssid, sdata->vif.addr, ETH_ALEN);
  	mgmt->u.action.category = WLAN_CATEGORY_SELF_PROTECTED;
  	mgmt->u.action.u.self_prot.action_code = action;
  
  	if (action != WLAN_SP_MESH_PEERING_CLOSE) {
  		struct ieee80211_supported_band *sband;
  		enum nl80211_band band;
  
  		sband = ieee80211_get_sband(sdata);
  		if (!sband) {
  			err = -EINVAL;
  			goto free;
  		}
  		band = sband->band;
  
  		/* capability info */
  		pos = skb_put_zero(skb, 2);
  		if (action == WLAN_SP_MESH_PEERING_CONFIRM) {
  			/* AID */
  			pos = skb_put(skb, 2);
  			put_unaligned_le16(sta->sta.aid, pos);
  		}
  		if (ieee80211_add_srates_ie(sdata, skb, true, band) ||
  		    ieee80211_add_ext_srates_ie(sdata, skb, true, band) ||
  		    mesh_add_rsn_ie(sdata, skb) ||
  		    mesh_add_meshid_ie(sdata, skb) ||
  		    mesh_add_meshconf_ie(sdata, skb))
  			goto free;
  	} else {	/* WLAN_SP_MESH_PEERING_CLOSE */
  		info->flags |= IEEE80211_TX_CTL_NO_ACK;
  		if (mesh_add_meshid_ie(sdata, skb))
  			goto free;
  	}
  
  	/* Add Mesh Peering Management element */
  	switch (action) {
  	case WLAN_SP_MESH_PEERING_OPEN:
  		break;
  	case WLAN_SP_MESH_PEERING_CONFIRM:
  		ie_len += 2;
  		include_plid = true;
  		break;
  	case WLAN_SP_MESH_PEERING_CLOSE:
  		if (plid) {
  			ie_len += 2;
  			include_plid = true;
  		}
  		ie_len += 2;	/* reason code */
  		break;
  	default:
  		err = -EINVAL;
  		goto free;
  	}
  
  	if (WARN_ON(skb_tailroom(skb) < 2 + ie_len))
  		goto free;
  
  	pos = skb_put(skb, 2 + ie_len);
  	*pos++ = WLAN_EID_PEER_MGMT;
  	*pos++ = ie_len;
  	memcpy(pos, &peering_proto, 2);
  	pos += 2;
  	put_unaligned_le16(llid, pos);
  	pos += 2;
  	if (include_plid) {
  		put_unaligned_le16(plid, pos);
  		pos += 2;
  	}
  	if (action == WLAN_SP_MESH_PEERING_CLOSE) {
  		put_unaligned_le16(reason, pos);
  		pos += 2;
  	}
  
  	if (action != WLAN_SP_MESH_PEERING_CLOSE) {
  		if (mesh_add_ht_cap_ie(sdata, skb) ||
  		    mesh_add_ht_oper_ie(sdata, skb) ||
  		    mesh_add_vht_cap_ie(sdata, skb) ||
  		    mesh_add_vht_oper_ie(sdata, skb) ||
  		    mesh_add_he_cap_ie(sdata, skb, ie_len_he_cap) ||
  		    mesh_add_he_oper_ie(sdata, skb) ||
  		    mesh_add_he_6ghz_cap_ie(sdata, skb))
  			goto free;
  	}
  
  	if (mesh_add_vendor_ies(sdata, skb))
  		goto free;
  
  	ieee80211_tx_skb(sdata, skb);
  	return 0;
  free:
  	kfree_skb(skb);
  	return err;
  }
  
  /**
   * __mesh_plink_deactivate - deactivate mesh peer link
   *
   * @sta: mesh peer link to deactivate
   *
   * Mesh paths with this peer as next hop should be flushed
   * by the caller outside of plink_lock.
   *
   * Returns beacon changed flag if the beacon content changed.
   *
   * Locking: the caller must hold sta->mesh->plink_lock
   */
  static u32 __mesh_plink_deactivate(struct sta_info *sta)
  {
  	struct ieee80211_sub_if_data *sdata = sta->sdata;
  	u32 changed = 0;
  
  	lockdep_assert_held(&sta->mesh->plink_lock);
  
  	if (sta->mesh->plink_state == NL80211_PLINK_ESTAB)
  		changed = mesh_plink_dec_estab_count(sdata);
  	sta->mesh->plink_state = NL80211_PLINK_BLOCKED;
  
  	ieee80211_mps_sta_status_update(sta);
  	changed |= ieee80211_mps_set_sta_local_pm(sta,
  			NL80211_MESH_POWER_UNKNOWN);
  
  	return changed;
  }
  
  /**
   * mesh_plink_deactivate - deactivate mesh peer link
   *
   * @sta: mesh peer link to deactivate
   *
   * All mesh paths with this peer as next hop will be flushed
   */
  u32 mesh_plink_deactivate(struct sta_info *sta)
  {
  	struct ieee80211_sub_if_data *sdata = sta->sdata;
  	u32 changed;
  
  	spin_lock_bh(&sta->mesh->plink_lock);
  	changed = __mesh_plink_deactivate(sta);
  
  	if (!sdata->u.mesh.user_mpm) {
  		sta->mesh->reason = WLAN_REASON_MESH_PEER_CANCELED;
  		mesh_plink_frame_tx(sdata, sta, WLAN_SP_MESH_PEERING_CLOSE,
  				    sta->sta.addr, sta->mesh->llid,
  				    sta->mesh->plid, sta->mesh->reason);
  	}
  	spin_unlock_bh(&sta->mesh->plink_lock);
  	if (!sdata->u.mesh.user_mpm)
  		del_timer_sync(&sta->mesh->plink_timer);
  	mesh_path_flush_by_nexthop(sta);
  
  	/* make sure no readers can access nexthop sta from here on */
  	synchronize_net();
  
  	return changed;
  }
  
  static void mesh_sta_info_init(struct ieee80211_sub_if_data *sdata,
  			       struct sta_info *sta,
  			       struct ieee802_11_elems *elems)
  {
  	struct ieee80211_local *local = sdata->local;
  	struct ieee80211_supported_band *sband;
  	u32 rates, basic_rates = 0, changed = 0;
  	enum ieee80211_sta_rx_bandwidth bw = sta->sta.bandwidth;
  
  	sband = ieee80211_get_sband(sdata);
  	if (!sband)
  		return;
  
  	rates = ieee80211_sta_get_rates(sdata, elems, sband->band,
  					&basic_rates);
  
  	spin_lock_bh(&sta->mesh->plink_lock);
  	sta->rx_stats.last_rx = jiffies;
  
  	/* rates and capabilities don't change during peering */
  	if (sta->mesh->plink_state == NL80211_PLINK_ESTAB &&
  	    sta->mesh->processed_beacon)
  		goto out;
  	sta->mesh->processed_beacon = true;
  
  	if (sta->sta.supp_rates[sband->band] != rates)
  		changed |= IEEE80211_RC_SUPP_RATES_CHANGED;
  	sta->sta.supp_rates[sband->band] = rates;
  
  	if (ieee80211_ht_cap_ie_to_sta_ht_cap(sdata, sband,
  					      elems->ht_cap_elem, sta))
  		changed |= IEEE80211_RC_BW_CHANGED;
  
  	ieee80211_vht_cap_ie_to_sta_vht_cap(sdata, sband,
  					    elems->vht_cap_elem, sta);
  
  	ieee80211_he_cap_ie_to_sta_he_cap(sdata, sband, elems->he_cap,
  					  elems->he_cap_len,
  					  elems->he_6ghz_capa,
  					  sta);
  
  	if (bw != sta->sta.bandwidth)
  		changed |= IEEE80211_RC_BW_CHANGED;
  
  	/* HT peer is operating 20MHz-only */
  	if (elems->ht_operation &&
  	    !(elems->ht_operation->ht_param &
  	      IEEE80211_HT_PARAM_CHAN_WIDTH_ANY)) {
  		if (sta->sta.bandwidth != IEEE80211_STA_RX_BW_20)
  			changed |= IEEE80211_RC_BW_CHANGED;
  		sta->sta.bandwidth = IEEE80211_STA_RX_BW_20;
  	}
  
  	if (!test_sta_flag(sta, WLAN_STA_RATE_CONTROL))
  		rate_control_rate_init(sta);
  	else
  		rate_control_rate_update(local, sband, sta, changed);
  out:
  	spin_unlock_bh(&sta->mesh->plink_lock);
  }
  
  static int mesh_allocate_aid(struct ieee80211_sub_if_data *sdata)
  {
  	struct sta_info *sta;
  	unsigned long *aid_map;
  	int aid;
  
  	aid_map = kcalloc(BITS_TO_LONGS(IEEE80211_MAX_AID + 1),
  			  sizeof(*aid_map), GFP_KERNEL);
  	if (!aid_map)
  		return -ENOMEM;
  
  	/* reserve aid 0 for mcast indication */
  	__set_bit(0, aid_map);
  
  	rcu_read_lock();
  	list_for_each_entry_rcu(sta, &sdata->local->sta_list, list)
  		__set_bit(sta->sta.aid, aid_map);
  	rcu_read_unlock();
  
  	aid = find_first_zero_bit(aid_map, IEEE80211_MAX_AID + 1);
  	kfree(aid_map);
  
  	if (aid > IEEE80211_MAX_AID)
  		return -ENOBUFS;
  
  	return aid;
  }
  
  static struct sta_info *
  __mesh_sta_info_alloc(struct ieee80211_sub_if_data *sdata, u8 *hw_addr)
  {
  	struct sta_info *sta;
  	int aid;
  
  	if (sdata->local->num_sta >= MESH_MAX_PLINKS)
  		return NULL;
  
  	aid = mesh_allocate_aid(sdata);
  	if (aid < 0)
  		return NULL;
  
  	sta = sta_info_alloc(sdata, hw_addr, GFP_KERNEL);
  	if (!sta)
  		return NULL;
  
  	sta->mesh->plink_state = NL80211_PLINK_LISTEN;
  	sta->sta.wme = true;
  	sta->sta.aid = aid;
  
  	sta_info_pre_move_state(sta, IEEE80211_STA_AUTH);
  	sta_info_pre_move_state(sta, IEEE80211_STA_ASSOC);
  	sta_info_pre_move_state(sta, IEEE80211_STA_AUTHORIZED);
  
  	return sta;
  }
  
  static struct sta_info *
  mesh_sta_info_alloc(struct ieee80211_sub_if_data *sdata, u8 *addr,
  		    struct ieee802_11_elems *elems,
  		    struct ieee80211_rx_status *rx_status)
  {
  	struct sta_info *sta = NULL;
  
  	/* Userspace handles station allocation */
  	if (sdata->u.mesh.user_mpm ||
  	    sdata->u.mesh.security & IEEE80211_MESH_SEC_AUTHED) {
  		if (mesh_peer_accepts_plinks(elems) &&
  		    mesh_plink_availables(sdata)) {
  			int sig = 0;
  
  			if (ieee80211_hw_check(&sdata->local->hw, SIGNAL_DBM))
  				sig = rx_status->signal;
  
  			cfg80211_notify_new_peer_candidate(sdata->dev, addr,
  							   elems->ie_start,
  							   elems->total_len,
  							   sig, GFP_KERNEL);
  		}
  	} else
  		sta = __mesh_sta_info_alloc(sdata, addr);
  
  	return sta;
  }
  
  /*
   * mesh_sta_info_get - return mesh sta info entry for @addr.
   *
   * @sdata: local meshif
   * @addr: peer's address
   * @elems: IEs from beacon or mesh peering frame.
   * @rx_status: rx status for the frame for signal reporting
   *
   * Return existing or newly allocated sta_info under RCU read lock.
   * (re)initialize with given IEs.
   */
  static struct sta_info *
  mesh_sta_info_get(struct ieee80211_sub_if_data *sdata,
  		  u8 *addr, struct ieee802_11_elems *elems,
  		  struct ieee80211_rx_status *rx_status) __acquires(RCU)
  {
  	struct sta_info *sta = NULL;
  
  	rcu_read_lock();
  	sta = sta_info_get(sdata, addr);
  	if (sta) {
  		mesh_sta_info_init(sdata, sta, elems);
  	} else {
  		rcu_read_unlock();
  		/* can't run atomic */
  		sta = mesh_sta_info_alloc(sdata, addr, elems, rx_status);
  		if (!sta) {
  			rcu_read_lock();
  			return NULL;
  		}
  
  		mesh_sta_info_init(sdata, sta, elems);
  
  		if (sta_info_insert_rcu(sta))
  			return NULL;
  	}
  
  	return sta;
  }
  
  /*
   * mesh_neighbour_update - update or initialize new mesh neighbor.
   *
   * @sdata: local meshif
   * @addr: peer's address
   * @elems: IEs from beacon or mesh peering frame
   * @rx_status: rx status for the frame for signal reporting
   *
   * Initiates peering if appropriate.
   */
  void mesh_neighbour_update(struct ieee80211_sub_if_data *sdata,
  			   u8 *hw_addr,
  			   struct ieee802_11_elems *elems,
  			   struct ieee80211_rx_status *rx_status)
  {
  	struct sta_info *sta;
  	u32 changed = 0;
  
  	sta = mesh_sta_info_get(sdata, hw_addr, elems, rx_status);
  	if (!sta)
  		goto out;
  
  	sta->mesh->connected_to_gate = elems->mesh_config->meshconf_form &
  		IEEE80211_MESHCONF_FORM_CONNECTED_TO_GATE;
  
  	if (mesh_peer_accepts_plinks(elems) &&
  	    sta->mesh->plink_state == NL80211_PLINK_LISTEN &&
  	    sdata->u.mesh.accepting_plinks &&
  	    sdata->u.mesh.mshcfg.auto_open_plinks &&
  	    rssi_threshold_check(sdata, sta))
  		changed = mesh_plink_open(sta);
  
  	ieee80211_mps_frame_release(sta, elems);
  out:
  	rcu_read_unlock();
  	ieee80211_mbss_info_change_notify(sdata, changed);
  }
  
  void mesh_plink_timer(struct timer_list *t)
  {
  	struct mesh_sta *mesh = from_timer(mesh, t, plink_timer);
  	struct sta_info *sta;
  	u16 reason = 0;
  	struct ieee80211_sub_if_data *sdata;
  	struct mesh_config *mshcfg;
  	enum ieee80211_self_protected_actioncode action = 0;
  
  	/*
  	 * This STA is valid because sta_info_destroy() will
  	 * del_timer_sync() this timer after having made sure
  	 * it cannot be readded (by deleting the plink.)
  	 */
  	sta = mesh->plink_sta;
  
  	if (sta->sdata->local->quiescing)
  		return;
  
  	spin_lock_bh(&sta->mesh->plink_lock);
  
  	/* If a timer fires just before a state transition on another CPU,
  	 * we may have already extended the timeout and changed state by the
  	 * time we've acquired the lock and arrived  here.  In that case,
  	 * skip this timer and wait for the new one.
  	 */
  	if (time_before(jiffies, sta->mesh->plink_timer.expires)) {
  		mpl_dbg(sta->sdata,
  			"Ignoring timer for %pM in state %s (timer adjusted)",
  			sta->sta.addr, mplstates[sta->mesh->plink_state]);
  		spin_unlock_bh(&sta->mesh->plink_lock);
  		return;
  	}
  
  	/* del_timer() and handler may race when entering these states */
  	if (sta->mesh->plink_state == NL80211_PLINK_LISTEN ||
  	    sta->mesh->plink_state == NL80211_PLINK_ESTAB) {
  		mpl_dbg(sta->sdata,
  			"Ignoring timer for %pM in state %s (timer deleted)",
  			sta->sta.addr, mplstates[sta->mesh->plink_state]);
  		spin_unlock_bh(&sta->mesh->plink_lock);
  		return;
  	}
  
  	mpl_dbg(sta->sdata,
  		"Mesh plink timer for %pM fired on state %s\n",
  		sta->sta.addr, mplstates[sta->mesh->plink_state]);
  	sdata = sta->sdata;
  	mshcfg = &sdata->u.mesh.mshcfg;
  
  	switch (sta->mesh->plink_state) {
  	case NL80211_PLINK_OPN_RCVD:
  	case NL80211_PLINK_OPN_SNT:
  		/* retry timer */
  		if (sta->mesh->plink_retries < mshcfg->dot11MeshMaxRetries) {
  			u32 rand;
  			mpl_dbg(sta->sdata,
  				"Mesh plink for %pM (retry, timeout): %d %d\n",
  				sta->sta.addr, sta->mesh->plink_retries,
  				sta->mesh->plink_timeout);
  			get_random_bytes(&rand, sizeof(u32));
  			sta->mesh->plink_timeout = sta->mesh->plink_timeout +
  					     rand % sta->mesh->plink_timeout;
  			++sta->mesh->plink_retries;
  			mod_plink_timer(sta, sta->mesh->plink_timeout);
  			action = WLAN_SP_MESH_PEERING_OPEN;
  			break;
  		}
  		reason = WLAN_REASON_MESH_MAX_RETRIES;
  		fallthrough;
  	case NL80211_PLINK_CNF_RCVD:
  		/* confirm timer */
  		if (!reason)
  			reason = WLAN_REASON_MESH_CONFIRM_TIMEOUT;
  		sta->mesh->plink_state = NL80211_PLINK_HOLDING;
  		mod_plink_timer(sta, mshcfg->dot11MeshHoldingTimeout);
  		action = WLAN_SP_MESH_PEERING_CLOSE;
  		break;
  	case NL80211_PLINK_HOLDING:
  		/* holding timer */
  		del_timer(&sta->mesh->plink_timer);
  		mesh_plink_fsm_restart(sta);
  		break;
  	default:
  		break;
  	}
  	spin_unlock_bh(&sta->mesh->plink_lock);
  	if (action)
  		mesh_plink_frame_tx(sdata, sta, action, sta->sta.addr,
  				    sta->mesh->llid, sta->mesh->plid, reason);
  }
  
  static inline void mesh_plink_timer_set(struct sta_info *sta, u32 timeout)
  {
  	sta->mesh->plink_timeout = timeout;
  	mod_timer(&sta->mesh->plink_timer, jiffies + msecs_to_jiffies(timeout));
  }
  
  static bool llid_in_use(struct ieee80211_sub_if_data *sdata,
  			u16 llid)
  {
  	struct ieee80211_local *local = sdata->local;
  	bool in_use = false;
  	struct sta_info *sta;
  
  	rcu_read_lock();
  	list_for_each_entry_rcu(sta, &local->sta_list, list) {
  		if (sdata != sta->sdata)
  			continue;
  
  		if (!memcmp(&sta->mesh->llid, &llid, sizeof(llid))) {
  			in_use = true;
  			break;
  		}
  	}
  	rcu_read_unlock();
  
  	return in_use;
  }
  
  static u16 mesh_get_new_llid(struct ieee80211_sub_if_data *sdata)
  {
  	u16 llid;
  
  	do {
  		get_random_bytes(&llid, sizeof(llid));
  	} while (llid_in_use(sdata, llid));
  
  	return llid;
  }
  
  u32 mesh_plink_open(struct sta_info *sta)
  {
  	struct ieee80211_sub_if_data *sdata = sta->sdata;
  	u32 changed;
  
  	if (!test_sta_flag(sta, WLAN_STA_AUTH))
  		return 0;
  
  	spin_lock_bh(&sta->mesh->plink_lock);
  	sta->mesh->llid = mesh_get_new_llid(sdata);
  	if (sta->mesh->plink_state != NL80211_PLINK_LISTEN &&
  	    sta->mesh->plink_state != NL80211_PLINK_BLOCKED) {
  		spin_unlock_bh(&sta->mesh->plink_lock);
  		return 0;
  	}
  	sta->mesh->plink_state = NL80211_PLINK_OPN_SNT;
  	mesh_plink_timer_set(sta, sdata->u.mesh.mshcfg.dot11MeshRetryTimeout);
  	spin_unlock_bh(&sta->mesh->plink_lock);
  	mpl_dbg(sdata,
  		"Mesh plink: starting establishment with %pM\n",
  		sta->sta.addr);
  
  	/* set the non-peer mode to active during peering */
  	changed = ieee80211_mps_local_status_update(sdata);
  
  	mesh_plink_frame_tx(sdata, sta, WLAN_SP_MESH_PEERING_OPEN,
  			    sta->sta.addr, sta->mesh->llid, 0, 0);
  	return changed;
  }
  
  u32 mesh_plink_block(struct sta_info *sta)
  {
  	u32 changed;
  
  	spin_lock_bh(&sta->mesh->plink_lock);
  	changed = __mesh_plink_deactivate(sta);
  	sta->mesh->plink_state = NL80211_PLINK_BLOCKED;
  	spin_unlock_bh(&sta->mesh->plink_lock);
  	mesh_path_flush_by_nexthop(sta);
  
  	return changed;
  }
  
  static void mesh_plink_close(struct ieee80211_sub_if_data *sdata,
  			     struct sta_info *sta,
  			     enum plink_event event)
  {
  	struct mesh_config *mshcfg = &sdata->u.mesh.mshcfg;
  	u16 reason = (event == CLS_ACPT) ?
  		     WLAN_REASON_MESH_CLOSE : WLAN_REASON_MESH_CONFIG;
  
  	sta->mesh->reason = reason;
  	sta->mesh->plink_state = NL80211_PLINK_HOLDING;
  	mod_plink_timer(sta, mshcfg->dot11MeshHoldingTimeout);
  }
  
  static u32 mesh_plink_establish(struct ieee80211_sub_if_data *sdata,
  				struct sta_info *sta)
  {
  	struct mesh_config *mshcfg = &sdata->u.mesh.mshcfg;
  	u32 changed = 0;
  
  	del_timer(&sta->mesh->plink_timer);
  	sta->mesh->plink_state = NL80211_PLINK_ESTAB;
  	changed |= mesh_plink_inc_estab_count(sdata);
  	changed |= mesh_set_ht_prot_mode(sdata);
  	changed |= mesh_set_short_slot_time(sdata);
  	mpl_dbg(sdata, "Mesh plink with %pM ESTABLISHED\n", sta->sta.addr);
  	ieee80211_mps_sta_status_update(sta);
  	changed |= ieee80211_mps_set_sta_local_pm(sta, mshcfg->power_mode);
  	return changed;
  }
  
  /**
   * mesh_plink_fsm - step @sta MPM based on @event
   *
   * @sdata: interface
   * @sta: mesh neighbor
   * @event: peering event
   *
   * Return: changed MBSS flags
   */
  static u32 mesh_plink_fsm(struct ieee80211_sub_if_data *sdata,
  			  struct sta_info *sta, enum plink_event event)
  {
  	struct mesh_config *mshcfg = &sdata->u.mesh.mshcfg;
  	enum ieee80211_self_protected_actioncode action = 0;
  	u32 changed = 0;
  	bool flush = false;
  
  	mpl_dbg(sdata, "peer %pM in state %s got event %s\n", sta->sta.addr,
  		mplstates[sta->mesh->plink_state], mplevents[event]);
  
  	spin_lock_bh(&sta->mesh->plink_lock);
  	switch (sta->mesh->plink_state) {
  	case NL80211_PLINK_LISTEN:
  		switch (event) {
  		case CLS_ACPT:
  			mesh_plink_fsm_restart(sta);
  			break;
  		case OPN_ACPT:
  			sta->mesh->plink_state = NL80211_PLINK_OPN_RCVD;
  			sta->mesh->llid = mesh_get_new_llid(sdata);
  			mesh_plink_timer_set(sta,
  					     mshcfg->dot11MeshRetryTimeout);
  
  			/* set the non-peer mode to active during peering */
  			changed |= ieee80211_mps_local_status_update(sdata);
  			action = WLAN_SP_MESH_PEERING_OPEN;
  			break;
  		default:
  			break;
  		}
  		break;
  	case NL80211_PLINK_OPN_SNT:
  		switch (event) {
  		case OPN_RJCT:
  		case CNF_RJCT:
  		case CLS_ACPT:
  			mesh_plink_close(sdata, sta, event);
  			action = WLAN_SP_MESH_PEERING_CLOSE;
  			break;
  		case OPN_ACPT:
  			/* retry timer is left untouched */
  			sta->mesh->plink_state = NL80211_PLINK_OPN_RCVD;
  			action = WLAN_SP_MESH_PEERING_CONFIRM;
  			break;
  		case CNF_ACPT:
  			sta->mesh->plink_state = NL80211_PLINK_CNF_RCVD;
  			mod_plink_timer(sta, mshcfg->dot11MeshConfirmTimeout);
  			break;
  		default:
  			break;
  		}
  		break;
  	case NL80211_PLINK_OPN_RCVD:
  		switch (event) {
  		case OPN_RJCT:
  		case CNF_RJCT:
  		case CLS_ACPT:
  			mesh_plink_close(sdata, sta, event);
  			action = WLAN_SP_MESH_PEERING_CLOSE;
  			break;
  		case OPN_ACPT:
  			action = WLAN_SP_MESH_PEERING_CONFIRM;
  			break;
  		case CNF_ACPT:
  			changed |= mesh_plink_establish(sdata, sta);
  			break;
  		default:
  			break;
  		}
  		break;
  	case NL80211_PLINK_CNF_RCVD:
  		switch (event) {
  		case OPN_RJCT:
  		case CNF_RJCT:
  		case CLS_ACPT:
  			mesh_plink_close(sdata, sta, event);
  			action = WLAN_SP_MESH_PEERING_CLOSE;
  			break;
  		case OPN_ACPT:
  			changed |= mesh_plink_establish(sdata, sta);
  			action = WLAN_SP_MESH_PEERING_CONFIRM;
  			break;
  		default:
  			break;
  		}
  		break;
  	case NL80211_PLINK_ESTAB:
  		switch (event) {
  		case CLS_ACPT:
  			changed |= __mesh_plink_deactivate(sta);
  			changed |= mesh_set_ht_prot_mode(sdata);
  			changed |= mesh_set_short_slot_time(sdata);
  			mesh_plink_close(sdata, sta, event);
  			action = WLAN_SP_MESH_PEERING_CLOSE;
  			flush = true;
  			break;
  		case OPN_ACPT:
  			action = WLAN_SP_MESH_PEERING_CONFIRM;
  			break;
  		default:
  			break;
  		}
  		break;
  	case NL80211_PLINK_HOLDING:
  		switch (event) {
  		case CLS_ACPT:
  			del_timer(&sta->mesh->plink_timer);
  			mesh_plink_fsm_restart(sta);
  			break;
  		case OPN_ACPT:
  		case CNF_ACPT:
  		case OPN_RJCT:
  		case CNF_RJCT:
  			action = WLAN_SP_MESH_PEERING_CLOSE;
  			break;
  		default:
  			break;
  		}
  		break;
  	default:
  		/* should not get here, PLINK_BLOCKED is dealt with at the
  		 * beginning of the function
  		 */
  		break;
  	}
  	spin_unlock_bh(&sta->mesh->plink_lock);
  	if (flush)
  		mesh_path_flush_by_nexthop(sta);
  	if (action) {
  		mesh_plink_frame_tx(sdata, sta, action, sta->sta.addr,
  				    sta->mesh->llid, sta->mesh->plid,
  				    sta->mesh->reason);
  
  		/* also send confirm in open case */
  		if (action == WLAN_SP_MESH_PEERING_OPEN) {
  			mesh_plink_frame_tx(sdata, sta,
  					    WLAN_SP_MESH_PEERING_CONFIRM,
  					    sta->sta.addr, sta->mesh->llid,
  					    sta->mesh->plid, 0);
  		}
  	}
  
  	return changed;
  }
  
  /*
   * mesh_plink_get_event - get correct MPM event
   *
   * @sdata: interface
   * @sta: peer, leave NULL if processing a frame from a new suitable peer
   * @elems: peering management IEs
   * @ftype: frame type
   * @llid: peer's peer link ID
   * @plid: peer's local link ID
   *
   * Return: new peering event for @sta, but PLINK_UNDEFINED should be treated as
   * an error.
   */
  static enum plink_event
  mesh_plink_get_event(struct ieee80211_sub_if_data *sdata,
  		     struct sta_info *sta,
  		     struct ieee802_11_elems *elems,
  		     enum ieee80211_self_protected_actioncode ftype,
  		     u16 llid, u16 plid)
  {
  	enum plink_event event = PLINK_UNDEFINED;
  	u8 ie_len = elems->peering_len;
  	bool matches_local;
  
  	matches_local = (ftype == WLAN_SP_MESH_PEERING_CLOSE ||
  			 mesh_matches_local(sdata, elems));
  
  	/* deny open request from non-matching peer */
  	if (!matches_local && !sta) {
  		event = OPN_RJCT;
  		goto out;
  	}
  
  	if (!sta) {
  		if (ftype != WLAN_SP_MESH_PEERING_OPEN) {
  			mpl_dbg(sdata, "Mesh plink: cls or cnf from unknown peer\n");
  			goto out;
  		}
  		/* ftype == WLAN_SP_MESH_PEERING_OPEN */
  		if (!mesh_plink_free_count(sdata)) {
  			mpl_dbg(sdata, "Mesh plink error: no more free plinks\n");
  			goto out;
  		}
  
  		/* new matching peer */
  		event = OPN_ACPT;
  		goto out;
  	} else {
  		if (!test_sta_flag(sta, WLAN_STA_AUTH)) {
  			mpl_dbg(sdata, "Mesh plink: Action frame from non-authed peer\n");
  			goto out;
  		}
  		if (sta->mesh->plink_state == NL80211_PLINK_BLOCKED)
  			goto out;
  	}
  
  	switch (ftype) {
  	case WLAN_SP_MESH_PEERING_OPEN:
  		if (!matches_local)
  			event = OPN_RJCT;
  		if (!mesh_plink_free_count(sdata) ||
  		    (sta->mesh->plid && sta->mesh->plid != plid))
  			event = OPN_IGNR;
  		else
  			event = OPN_ACPT;
  		break;
  	case WLAN_SP_MESH_PEERING_CONFIRM:
  		if (!matches_local)
  			event = CNF_RJCT;
  		if (!mesh_plink_free_count(sdata) ||
  		    sta->mesh->llid != llid ||
  		    (sta->mesh->plid && sta->mesh->plid != plid))
  			event = CNF_IGNR;
  		else
  			event = CNF_ACPT;
  		break;
  	case WLAN_SP_MESH_PEERING_CLOSE:
  		if (sta->mesh->plink_state == NL80211_PLINK_ESTAB)
  			/* Do not check for llid or plid. This does not
  			 * follow the standard but since multiple plinks
  			 * per sta are not supported, it is necessary in
  			 * order to avoid a livelock when MP A sees an
  			 * establish peer link to MP B but MP B does not
  			 * see it. This can be caused by a timeout in
  			 * B's peer link establishment or B beign
  			 * restarted.
  			 */
  			event = CLS_ACPT;
  		else if (sta->mesh->plid != plid)
  			event = CLS_IGNR;
  		else if (ie_len == 8 && sta->mesh->llid != llid)
  			event = CLS_IGNR;
  		else
  			event = CLS_ACPT;
  		break;
  	default:
  		mpl_dbg(sdata, "Mesh plink: unknown frame subtype\n");
  		break;
  	}
  
  out:
  	return event;
  }
  
  static void
  mesh_process_plink_frame(struct ieee80211_sub_if_data *sdata,
  			 struct ieee80211_mgmt *mgmt,
  			 struct ieee802_11_elems *elems,
  			 struct ieee80211_rx_status *rx_status)
  {
  
  	struct sta_info *sta;
  	enum plink_event event;
  	enum ieee80211_self_protected_actioncode ftype;
  	u32 changed = 0;
  	u8 ie_len = elems->peering_len;
  	u16 plid, llid = 0;
  
  	if (!elems->peering) {
  		mpl_dbg(sdata,
  			"Mesh plink: missing necessary peer link ie\n");
  		return;
  	}
  
  	if (elems->rsn_len &&
  	    sdata->u.mesh.security == IEEE80211_MESH_SEC_NONE) {
  		mpl_dbg(sdata,
  			"Mesh plink: can't establish link with secure peer\n");
  		return;
  	}
  
  	ftype = mgmt->u.action.u.self_prot.action_code;
  	if ((ftype == WLAN_SP_MESH_PEERING_OPEN && ie_len != 4) ||
  	    (ftype == WLAN_SP_MESH_PEERING_CONFIRM && ie_len != 6) ||
  	    (ftype == WLAN_SP_MESH_PEERING_CLOSE && ie_len != 6
  							&& ie_len != 8)) {
  		mpl_dbg(sdata,
  			"Mesh plink: incorrect plink ie length %d %d\n",
  			ftype, ie_len);
  		return;
  	}
  
  	if (ftype != WLAN_SP_MESH_PEERING_CLOSE &&
  	    (!elems->mesh_id || !elems->mesh_config)) {
  		mpl_dbg(sdata, "Mesh plink: missing necessary ie\n");
  		return;
  	}
  	/* Note the lines below are correct, the llid in the frame is the plid
  	 * from the point of view of this host.
  	 */
  	plid = get_unaligned_le16(PLINK_GET_LLID(elems->peering));
  	if (ftype == WLAN_SP_MESH_PEERING_CONFIRM ||
  	    (ftype == WLAN_SP_MESH_PEERING_CLOSE && ie_len == 8))
  		llid = get_unaligned_le16(PLINK_GET_PLID(elems->peering));
  
  	/* WARNING: Only for sta pointer, is dropped & re-acquired */
  	rcu_read_lock();
  
  	sta = sta_info_get(sdata, mgmt->sa);
  
  	if (ftype == WLAN_SP_MESH_PEERING_OPEN &&
  	    !rssi_threshold_check(sdata, sta)) {
  		mpl_dbg(sdata, "Mesh plink: %pM does not meet rssi threshold\n",
  			mgmt->sa);
  		goto unlock_rcu;
  	}
  
  	/* Now we will figure out the appropriate event... */
  	event = mesh_plink_get_event(sdata, sta, elems, ftype, llid, plid);
  
  	if (event == OPN_ACPT) {
  		rcu_read_unlock();
  		/* allocate sta entry if necessary and update info */
  		sta = mesh_sta_info_get(sdata, mgmt->sa, elems, rx_status);
  		if (!sta) {
  			mpl_dbg(sdata, "Mesh plink: failed to init peer!\n");
  			goto unlock_rcu;
  		}
  		sta->mesh->plid = plid;
  	} else if (!sta && event == OPN_RJCT) {
  		mesh_plink_frame_tx(sdata, NULL, WLAN_SP_MESH_PEERING_CLOSE,
  				    mgmt->sa, 0, plid,
  				    WLAN_REASON_MESH_CONFIG);
  		goto unlock_rcu;
  	} else if (!sta || event == PLINK_UNDEFINED) {
  		/* something went wrong */
  		goto unlock_rcu;
  	}
  
  	if (event == CNF_ACPT) {
  		/* 802.11-2012 13.3.7.2 - update plid on CNF if not set */
  		if (!sta->mesh->plid)
  			sta->mesh->plid = plid;
  
  		sta->mesh->aid = get_unaligned_le16(PLINK_CNF_AID(mgmt));
  	}
  
  	changed |= mesh_plink_fsm(sdata, sta, event);
  
  unlock_rcu:
  	rcu_read_unlock();
  
  	if (changed)
  		ieee80211_mbss_info_change_notify(sdata, changed);
  }
  
  void mesh_rx_plink_frame(struct ieee80211_sub_if_data *sdata,
  			 struct ieee80211_mgmt *mgmt, size_t len,
  			 struct ieee80211_rx_status *rx_status)
  {
  	struct ieee802_11_elems *elems;
  	size_t baselen;
  	u8 *baseaddr;
  
  	/* need action_code, aux */
  	if (len < IEEE80211_MIN_ACTION_SIZE + 3)
  		return;
  
  	if (sdata->u.mesh.user_mpm)
  		/* userspace must register for these */
  		return;
  
  	if (is_multicast_ether_addr(mgmt->da)) {
  		mpl_dbg(sdata,
  			"Mesh plink: ignore frame from multicast address\n");
  		return;
  	}
  
  	baseaddr = mgmt->u.action.u.self_prot.variable;
  	baselen = (u8 *) mgmt->u.action.u.self_prot.variable - (u8 *) mgmt;
  	if (mgmt->u.action.u.self_prot.action_code ==
  						WLAN_SP_MESH_PEERING_CONFIRM) {
  		baseaddr += 4;
  		baselen += 4;
  
  		if (baselen > len)
  			return;
  	}
  	elems = ieee802_11_parse_elems(baseaddr, len - baselen, true,
  				       mgmt->bssid, NULL);
  	mesh_process_plink_frame(sdata, mgmt, elems, rx_status);
  	kfree(elems);
  }
  