net/mac80211/mesh_plink.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2008, 2009 open80211s Ltd.
 * Copyright (C) 2019, 2021-2026 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.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->deflink.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 u64 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;
	u64 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.deflink.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.
 *
 * Returns: BSS_CHANGED_HT or 0 for no change
 */
static u64 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.chanreq.oper.width) {
	case NL80211_CHAN_WIDTH_20_NOHT:
		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.deflink.bandwidth > IEEE80211_STA_RX_BW_20)
			continue;

		if (!sta->sta.deflink.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.chanreq.oper.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)
{
	int hdr_len = IEEE80211_MIN_ACTION_SIZE(self_prot);
	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, ie_len_eht_cap;
	int err = -ENOMEM;

	ie_len_he_cap = ieee80211_ie_len_he_cap(sdata);
	ie_len_eht_cap = ieee80211_ie_len_eht_cap(sdata);
	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) +
			    ie_len_eht_cap +
			    2 + 1 + offsetof(struct ieee80211_eht_operation, optional) +
				    offsetof(struct ieee80211_eht_operation_info, optional) +
			    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.action_code = action;

	if (action != WLAN_SP_MESH_PEERING_CLOSE) {
		struct ieee80211_supported_band *sband;
		u32 basic_rates;

		sband = ieee80211_get_sband(sdata);
		if (!sband) {
			err = -EINVAL;
			goto free;
		}

		/* 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);
		}

		basic_rates = sdata->vif.bss_conf.basic_rates;

		if (ieee80211_put_srates_elem(skb, sband, basic_rates,
					      0, WLAN_EID_SUPP_RATES) ||
		    ieee80211_put_srates_elem(skb, sband, basic_rates,
					      0, WLAN_EID_EXT_SUPP_RATES) ||
		    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) ||
		    mesh_add_eht_cap_ie(sdata, skb, ie_len_eht_cap) ||
		    mesh_add_eht_oper_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 u64 __mesh_plink_deactivate(struct sta_info *sta)
{
	struct ieee80211_sub_if_data *sdata = sta->sdata;
	u64 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
 *
 * Returns: beacon changed flag if the beacon content changed.
 */
u64 mesh_plink_deactivate(struct sta_info *sta)
{
	struct ieee80211_sub_if_data *sdata = sta->sdata;
	u64 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)
		timer_delete_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, changed = 0;
	enum ieee80211_sta_rx_bandwidth bw = sta->sta.deflink.bandwidth;

	sband = ieee80211_get_sband(sdata);
	if (!sband)
		return;

	rates = ieee80211_sta_get_rates(sdata, elems, sband->band, NULL);

	spin_lock_bh(&sta->mesh->plink_lock);
	sta->deflink.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.deflink.supp_rates[sband->band] != rates)
		changed |= IEEE80211_RC_SUPP_RATES_CHANGED;
	sta->sta.deflink.supp_rates[sband->band] = rates;

	if (ieee80211_ht_cap_ie_to_sta_ht_cap(sdata, &sband->ht_cap,
					      elems->ht_cap_elem,
					      &sta->deflink))
		changed |= IEEE80211_RC_BW_CHANGED;

	ieee80211_vht_cap_ie_to_sta_vht_cap(sdata, sband,
					    &sband->vht_cap,
					    elems->vht_cap_elem, NULL,
					    &sta->deflink);

	ieee80211_he_cap_ie_to_sta_he_cap(sdata, sband, elems->he_cap,
					  elems->he_cap_len,
					  elems->he_6ghz_capa,
					  &sta->deflink);

	ieee80211_eht_cap_ie_to_sta_eht_cap(sdata, sband, elems->he_cap,
					    elems->he_cap_len,
					    elems->eht_cap, elems->eht_cap_len,
					    &sta->deflink);

	ieee80211_sta_init_nss_bw_capa(&sta->deflink,
				       &sdata->deflink.conf->chanreq.oper);

	if (bw != sta->sta.deflink.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.deflink.bandwidth != IEEE80211_STA_RX_BW_20)
			changed |= IEEE80211_RC_BW_CHANGED;
		sta->sta.deflink.bandwidth = IEEE80211_STA_RX_BW_20;
	}

	/* FIXME: this check is wrong without SW rate control */
	if (!test_sta_flag(sta, WLAN_STA_RATE_CONTROL))
		rate_control_rate_init(&sta->deflink);
	else
		rate_control_rate_update(local, sband, &sta->deflink, 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 = bitmap_zalloc(IEEE80211_MAX_AID + 1, 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);
	bitmap_free(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;
	u64 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 = timer_container_of(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
	 * timer_delete_sync() this timer after having made sure
	 * it cannot be re-added (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;
	}

	/* timer_delete() 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);
			rand = get_random_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 */
		timer_delete(&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;
}

u64 mesh_plink_open(struct sta_info *sta)
{
	struct ieee80211_sub_if_data *sdata = sta->sdata;
	u64 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;
}

u64 mesh_plink_block(struct sta_info *sta)
{
	u64 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 u64 mesh_plink_establish(struct ieee80211_sub_if_data *sdata,
				struct sta_info *sta)
{
	struct mesh_config *mshcfg = &sdata->u.mesh.mshcfg;
	u64 changed = 0;

	timer_delete(&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 u64 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;
	u64 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:
			timer_delete(&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;
		else 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;
		else 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;
	u64 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.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 aux */
	if (len < IEEE80211_MIN_ACTION_SIZE(self_prot) + 1)
		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.self_prot.variable;
	baselen = mgmt->u.action.self_prot.variable - (u8 *)mgmt;
	if (mgmt->u.action.action_code == WLAN_SP_MESH_PEERING_CONFIRM) {
		baseaddr += 4;
		baselen += 4;

		if (baselen > len)
			return;
	}
	elems = ieee802_11_parse_elems(baseaddr, len - baselen,
				       IEEE80211_FTYPE_MGMT |
				       IEEE80211_STYPE_ACTION,
				       NULL);
	if (elems) {
		mesh_process_plink_frame(sdata, mgmt, elems, rx_status);
		kfree(elems);
	}
}