mac80211: make ieee80211_build_preq_ies safer

Instead of assuming 200 bytes are always enough for
all the IEs we add, give the length of the buffer
to the function and warn instead of overrunning.

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

net/mac80211/ieee80211_i.h

@@ -1034,6 +1034,7 @@ struct ieee80211_local {
 	enum ieee80211_band hw_scan_band;
 	int scan_channel_idx;
 	int scan_ies_len;
+	int hw_scan_ies_bufsize;
 
 	struct work_struct sched_scan_stopped_work;
 	struct ieee80211_sub_if_data __rcu *sched_scan_sdata;
@@ -1573,7 +1574,7 @@ void ieee80211_send_deauth_disassoc(struct ieee80211_sub_if_data *sdata,
 				    const u8 *bssid, u16 stype, u16 reason,
 				    bool send_frame, u8 *frame_buf);
 int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
-			     const u8 *ie, size_t ie_len,
+			     size_t buffer_len, const u8 *ie, size_t ie_len,
 			     enum ieee80211_band band, u32 rate_mask,
 			     u8 channel);
 struct sk_buff *ieee80211_build_probe_req(struct ieee80211_sub_if_data *sdata,

net/mac80211/scan.c

@@ -247,6 +247,7 @@ static bool ieee80211_prep_hw_scan(struct ieee80211_local *local)
 	local->hw_scan_req->n_channels = n_chans;
 
 	ielen = ieee80211_build_preq_ies(local, (u8 *)local->hw_scan_req->ie,
+					 local->hw_scan_ies_bufsize,
 					 req->ie, req->ie_len, band,
 					 req->rates[band], 0);
 	local->hw_scan_req->ie_len = ielen;
@@ -445,11 +446,13 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
 	if (local->ops->hw_scan) {
 		u8 *ies;
 
+		local->hw_scan_ies_bufsize = 2 + IEEE80211_MAX_SSID_LEN +
+					     local->scan_ies_len +
+					     req->ie_len;
 		local->hw_scan_req = kmalloc(
 				sizeof(*local->hw_scan_req) +
 				req->n_channels * sizeof(req->channels[0]) +
-				2 + IEEE80211_MAX_SSID_LEN + local->scan_ies_len +
-				req->ie_len, GFP_KERNEL);
+				local->hw_scan_ies_bufsize, GFP_KERNEL);
 		if (!local->hw_scan_req)
 			return -ENOMEM;
 
@@ -928,7 +931,10 @@ int ieee80211_request_sched_scan_start(struct ieee80211_sub_if_data *sdata,
 {
 	struct ieee80211_local *local = sdata->local;
 	struct ieee80211_sched_scan_ies sched_scan_ies;
-	int ret, i;
+	int ret, i, iebufsz;
+
+	iebufsz = 2 + IEEE80211_MAX_SSID_LEN +
+		  local->scan_ies_len + req->ie_len;
 
 	mutex_lock(&local->mtx);
 
@@ -946,10 +952,7 @@ int ieee80211_request_sched_scan_start(struct ieee80211_sub_if_data *sdata,
 		if (!local->hw.wiphy->bands[i])
 			continue;
 
-		sched_scan_ies.ie[i] = kzalloc(2 + IEEE80211_MAX_SSID_LEN +
-					       local->scan_ies_len +
-					       req->ie_len,
-					       GFP_KERNEL);
+		sched_scan_ies.ie[i] = kzalloc(iebufsz, GFP_KERNEL);
 		if (!sched_scan_ies.ie[i]) {
 			ret = -ENOMEM;
 			goto out_free;
@@ -957,8 +960,8 @@ int ieee80211_request_sched_scan_start(struct ieee80211_sub_if_data *sdata,
 
 		sched_scan_ies.len[i] =
 			ieee80211_build_preq_ies(local, sched_scan_ies.ie[i],
-						 req->ie, req->ie_len, i,
-						 (u32) -1, 0);
+						 iebufsz, req->ie, req->ie_len,
+						 i, (u32) -1, 0);
 	}
 
 	ret = drv_sched_scan_start(local, sdata, req, &sched_scan_ies);

net/mac80211/util.c

@@ -1107,12 +1107,12 @@ void ieee80211_send_deauth_disassoc(struct ieee80211_sub_if_data *sdata,
 }
 
 int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
-			     const u8 *ie, size_t ie_len,
+			     size_t buffer_len, const u8 *ie, size_t ie_len,
 			     enum ieee80211_band band, u32 rate_mask,
 			     u8 channel)
 {
 	struct ieee80211_supported_band *sband;
-	u8 *pos;
+	u8 *pos = buffer, *end = buffer + buffer_len;
 	size_t offset = 0, noffset;
 	int supp_rates_len, i;
 	u8 rates[32];
@@ -1123,8 +1123,6 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
 	if (WARN_ON_ONCE(!sband))
 		return 0;
 
-	pos = buffer;
-
 	num_rates = 0;
 	for (i = 0; i < sband->n_bitrates; i++) {
 		if ((BIT(i) & rate_mask) == 0)
@@ -1134,6 +1132,8 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
 
 	supp_rates_len = min_t(int, num_rates, 8);
 
+	if (end - pos < 2 + supp_rates_len)
+		goto out_err;
 	*pos++ = WLAN_EID_SUPP_RATES;
 	*pos++ = supp_rates_len;
 	memcpy(pos, rates, supp_rates_len);
@@ -1150,6 +1150,8 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
 					     before_extrates,
 					     ARRAY_SIZE(before_extrates),
 					     offset);
+		if (end - pos < noffset - offset)
+			goto out_err;
 		memcpy(pos, ie + offset, noffset - offset);
 		pos += noffset - offset;
 		offset = noffset;
@@ -1157,6 +1159,8 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
 
 	ext_rates_len = num_rates - supp_rates_len;
 	if (ext_rates_len > 0) {
+		if (end - pos < 2 + ext_rates_len)
+			goto out_err;
 		*pos++ = WLAN_EID_EXT_SUPP_RATES;
 		*pos++ = ext_rates_len;
 		memcpy(pos, rates + supp_rates_len, ext_rates_len);
@@ -1164,6 +1168,8 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
 	}
 
 	if (channel && sband->band == IEEE80211_BAND_2GHZ) {
+		if (end - pos < 3)
+			goto out_err;
 		*pos++ = WLAN_EID_DS_PARAMS;
 		*pos++ = 1;
 		*pos++ = channel;
@@ -1182,14 +1188,19 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
 		noffset = ieee80211_ie_split(ie, ie_len,
 					     before_ht, ARRAY_SIZE(before_ht),
 					     offset);
+		if (end - pos < noffset - offset)
+			goto out_err;
 		memcpy(pos, ie + offset, noffset - offset);
 		pos += noffset - offset;
 		offset = noffset;
 	}
 
-	if (sband->ht_cap.ht_supported)
+	if (sband->ht_cap.ht_supported) {
+		if (end - pos < 2 + sizeof(struct ieee80211_ht_cap))
+			goto out_err;
 		pos = ieee80211_ie_build_ht_cap(pos, &sband->ht_cap,
 						sband->ht_cap.cap);
+	}
 
 	/*
 	 * If adding more here, adjust code in main.c
@@ -1199,14 +1210,22 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
 	/* add any remaining custom IEs */
 	if (ie && ie_len) {
 		noffset = ie_len;
+		if (end - pos < noffset - offset)
+			goto out_err;
 		memcpy(pos, ie + offset, noffset - offset);
 		pos += noffset - offset;
 	}
 
-	if (sband->vht_cap.vht_supported)
+	if (sband->vht_cap.vht_supported) {
+		if (end - pos < 2 + sizeof(struct ieee80211_vht_cap))
+			goto out_err;
 		pos = ieee80211_ie_build_vht_cap(pos, &sband->vht_cap,
 						 sband->vht_cap.cap);
+	}
 
+	return pos - buffer;
+ out_err:
+	WARN_ONCE(1, "not enough space for preq IEs\n");
 	return pos - buffer;
 }
 
@@ -1239,7 +1258,8 @@ struct sk_buff *ieee80211_build_probe_req(struct ieee80211_sub_if_data *sdata,
 	else
 		chan_no = ieee80211_frequency_to_channel(chan->center_freq);
 
-	buf_len = ieee80211_build_preq_ies(local, buf, ie, ie_len, chan->band,
+	buf_len = ieee80211_build_preq_ies(local, buf, 200 + ie_len,
+					   ie, ie_len, chan->band,
 					   ratemask, chan_no);
 
 	skb = ieee80211_probereq_get(&local->hw, &sdata->vif,