cfg80211: fix BSS struct IE access races

When a BSS struct is updated, the IEs are currently
overwritten or freed. This can lead to races if some
other CPU is accessing the BSS struct and using the
IEs concurrently.

Fix this by always allocating the IEs in a new struct
that holds the data and length and protecting access
to this new struct with RCU.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 49 insertions, 31 deletions

diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 35d8cffc973a..481d5035b397 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -1382,19 +1382,26 @@ static void ieee80211_set_associated(struct ieee80211_sub_if_data *sdata,
 	sdata->u.mgd.flags |= IEEE80211_STA_RESET_SIGNAL_AVE;
 
 	if (sdata->vif.p2p) {
-		u8 noa[2];
-		int ret;
+		const struct cfg80211_bss_ies *ies;
 
-		ret = cfg80211_get_p2p_attr(cbss->information_elements,
-					    cbss->len_information_elements,
-					    IEEE80211_P2P_ATTR_ABSENCE_NOTICE,
-					    noa, sizeof(noa));
-		if (ret >= 2) {
-			bss_conf->p2p_oppps = noa[1] & 0x80;
-			bss_conf->p2p_ctwindow = noa[1] & 0x7f;
-			bss_info_changed |= BSS_CHANGED_P2P_PS;
-			sdata->u.mgd.p2p_noa_index = noa[0];
+		rcu_read_lock();
+		ies = rcu_dereference(cbss->ies);
+		if (ies) {
+			u8 noa[2];
+			int ret;
+
+			ret = cfg80211_get_p2p_attr(
+					ies->data, ies->len,
+					IEEE80211_P2P_ATTR_ABSENCE_NOTICE,
+					noa, sizeof(noa));
+			if (ret >= 2) {
+				bss_conf->p2p_oppps = noa[1] & 0x80;
+				bss_conf->p2p_ctwindow = noa[1] & 0x7f;
+				bss_info_changed |= BSS_CHANGED_P2P_PS;
+				sdata->u.mgd.p2p_noa_index = noa[0];
+			}
 		}
+		rcu_read_unlock();
 	}
 
 	/* just to be sure */
@@ -1659,6 +1666,7 @@ static void ieee80211_mgd_probe_ap_send(struct ieee80211_sub_if_data *sdata)
 	} else {
 		int ssid_len;
 
+		rcu_read_lock();
 		ssid = ieee80211_bss_get_ie(ifmgd->associated, WLAN_EID_SSID);
 		if (WARN_ON_ONCE(ssid == NULL))
 			ssid_len = 0;
@@ -1668,6 +1676,7 @@ static void ieee80211_mgd_probe_ap_send(struct ieee80211_sub_if_data *sdata)
 		ieee80211_send_probe_req(sdata, dst, ssid + 2, ssid_len, NULL,
 					 0, (u32) -1, true, false,
 					 ifmgd->associated->channel, false);
+		rcu_read_unlock();
 	}
 
 	ifmgd->probe_timeout = jiffies + msecs_to_jiffies(probe_wait_ms);
@@ -1763,6 +1772,7 @@ struct sk_buff *ieee80211_ap_probereq_get(struct ieee80211_hw *hw,
 	else
 		return NULL;
 
+	rcu_read_lock();
 	ssid = ieee80211_bss_get_ie(cbss, WLAN_EID_SSID);
 	if (WARN_ON_ONCE(ssid == NULL))
 		ssid_len = 0;
@@ -1773,6 +1783,7 @@ struct sk_buff *ieee80211_ap_probereq_get(struct ieee80211_hw *hw,
 					(u32) -1, cbss->channel,
 					ssid + 2, ssid_len,
 					NULL, 0, true);
+	rcu_read_unlock();
 
 	return skb;
 }
@@ -2858,9 +2869,12 @@ static int ieee80211_probe_auth(struct ieee80211_sub_if_data *sdata)
 			   auth_data->bss->bssid, auth_data->tries,
 			   IEEE80211_AUTH_MAX_TRIES);
 
+		rcu_read_lock();
 		ssidie = ieee80211_bss_get_ie(auth_data->bss, WLAN_EID_SSID);
-		if (!ssidie)
+		if (!ssidie) {
+			rcu_read_unlock();
 			return -EINVAL;
+		}
 		/*
 		 * Direct probe is sent to broadcast address as some APs
 		 * will not answer to direct packet in unassociated state.
@@ -2868,6 +2882,7 @@ static int ieee80211_probe_auth(struct ieee80211_sub_if_data *sdata)
 		ieee80211_send_probe_req(sdata, NULL, ssidie + 2, ssidie[1],
 					 NULL, 0, (u32) -1, true, false,
 					 auth_data->bss->channel, false);
+		rcu_read_unlock();
 	}
 
 	auth_data->timeout = jiffies + IEEE80211_AUTH_TIMEOUT;
@@ -3404,9 +3419,7 @@ static u8 ieee80211_ht_vht_rx_chains(struct ieee80211_sub_if_data *sdata,
 	if (ifmgd->flags & IEEE80211_STA_DISABLE_HT)
 		return chains;
 
-	ht_cap_ie = cfg80211_find_ie(WLAN_EID_HT_CAPABILITY,
-				     cbss->information_elements,
-				     cbss->len_information_elements);
+	ht_cap_ie = ieee80211_bss_get_ie(cbss, WLAN_EID_HT_CAPABILITY);
 	if (ht_cap_ie && ht_cap_ie[1] >= sizeof(*ht_cap)) {
 		ht_cap = (void *)(ht_cap_ie + 2);
 		chains = ieee80211_mcs_to_chains(&ht_cap->mcs);
@@ -3419,9 +3432,7 @@ static u8 ieee80211_ht_vht_rx_chains(struct ieee80211_sub_if_data *sdata,
 	if (ifmgd->flags & IEEE80211_STA_DISABLE_VHT)
 		return chains;
 
-	vht_cap_ie = cfg80211_find_ie(WLAN_EID_VHT_CAPABILITY,
-				      cbss->information_elements,
-				      cbss->len_information_elements);
+	vht_cap_ie = ieee80211_bss_get_ie(cbss, WLAN_EID_VHT_CAPABILITY);
 	if (vht_cap_ie && vht_cap_ie[1] >= sizeof(*vht_cap)) {
 		u8 nss;
 		u16 tx_mcs_map;
@@ -3457,13 +3468,13 @@ static int ieee80211_prep_channel(struct ieee80211_sub_if_data *sdata,
 			  IEEE80211_STA_DISABLE_80P80MHZ |
 			  IEEE80211_STA_DISABLE_160MHZ);
 
+	rcu_read_lock();
+
 	if (!(ifmgd->flags & IEEE80211_STA_DISABLE_HT) &&
 	    sband->ht_cap.ht_supported) {
 		const u8 *ht_oper_ie;
 
-		ht_oper_ie = cfg80211_find_ie(WLAN_EID_HT_OPERATION,
-					      cbss->information_elements,
-					      cbss->len_information_elements);
+		ht_oper_ie = ieee80211_bss_get_ie(cbss, WLAN_EID_HT_OPERATION);
 		if (ht_oper_ie && ht_oper_ie[1] >= sizeof(*ht_oper))
 			ht_oper = (void *)(ht_oper_ie + 2);
 	}
@@ -3472,9 +3483,8 @@ static int ieee80211_prep_channel(struct ieee80211_sub_if_data *sdata,
 	    sband->vht_cap.vht_supported) {
 		const u8 *vht_oper_ie;
 
-		vht_oper_ie = cfg80211_find_ie(WLAN_EID_VHT_OPERATION,
-					       cbss->information_elements,
-					       cbss->len_information_elements);
+		vht_oper_ie = ieee80211_bss_get_ie(cbss,
+						   WLAN_EID_VHT_OPERATION);
 		if (vht_oper_ie && vht_oper_ie[1] >= sizeof(*vht_oper))
 			vht_oper = (void *)(vht_oper_ie + 2);
 		if (vht_oper && !ht_oper) {
@@ -3494,6 +3504,8 @@ static int ieee80211_prep_channel(struct ieee80211_sub_if_data *sdata,
 	sdata->needed_rx_chains = min(ieee80211_ht_vht_rx_chains(sdata, cbss),
 				      local->rx_chains);
 
+	rcu_read_unlock();
+
 	/* will change later if needed */
 	sdata->smps_mode = IEEE80211_SMPS_OFF;
 
@@ -3734,14 +3746,21 @@ int ieee80211_mgd_assoc(struct ieee80211_sub_if_data *sdata,
 	const u8 *ssidie, *ht_ie;
 	int i, err;
 
-	ssidie = ieee80211_bss_get_ie(req->bss, WLAN_EID_SSID);
-	if (!ssidie)
-		return -EINVAL;
-
 	assoc_data = kzalloc(sizeof(*assoc_data) + req->ie_len, GFP_KERNEL);
 	if (!assoc_data)
 		return -ENOMEM;
 
+	rcu_read_lock();
+	ssidie = ieee80211_bss_get_ie(req->bss, WLAN_EID_SSID);
+	if (!ssidie) {
+		rcu_read_unlock();
+		kfree(assoc_data);
+		return -EINVAL;
+	}
+	memcpy(assoc_data->ssid, ssidie + 2, ssidie[1]);
+	assoc_data->ssid_len = ssidie[1];
+	rcu_read_unlock();
+
 	mutex_lock(&ifmgd->mtx);
 
 	if (ifmgd->associated)
@@ -3836,12 +3855,14 @@ int ieee80211_mgd_assoc(struct ieee80211_sub_if_data *sdata,
 	assoc_data->supp_rates = bss->supp_rates;
 	assoc_data->supp_rates_len = bss->supp_rates_len;
 
+	rcu_read_lock();
 	ht_ie = ieee80211_bss_get_ie(req->bss, WLAN_EID_HT_OPERATION);
 	if (ht_ie && ht_ie[1] >= sizeof(struct ieee80211_ht_operation))
 		assoc_data->ap_ht_param =
 			((struct ieee80211_ht_operation *)(ht_ie + 2))->ht_param;
 	else
 		ifmgd->flags |= IEEE80211_STA_DISABLE_HT;
+	rcu_read_unlock();
 
 	if (bss->wmm_used && bss->uapsd_supported &&
 	    (sdata->local->hw.flags & IEEE80211_HW_SUPPORTS_UAPSD)) {
@@ -3852,9 +3873,6 @@ int ieee80211_mgd_assoc(struct ieee80211_sub_if_data *sdata,
 		ifmgd->flags &= ~IEEE80211_STA_UAPSD_ENABLED;
 	}
 
-	memcpy(assoc_data->ssid, ssidie + 2, ssidie[1]);
-	assoc_data->ssid_len = ssidie[1];
-
 	if (req->prev_bssid)
 		memcpy(assoc_data->prev_bssid, req->prev_bssid, ETH_ALEN);