mac80211: Parse legacy and HT rate in injected frames

Drivers/devices without their own rate control algorithm can get the
information what rates they should use from either the radiotap header of
injected frames or from the rate control algorithm. But the parsing of the
legacy rate information from the radiotap header was removed in commit
e6a9854b ("mac80211/drivers: rewrite the rate control API").

The removal of this feature heavily reduced the usefulness of frame
injection when wanting to simulate specific transmission behavior. Having
rate parsing together with MCS rates and retry support allows a fine
grained selection of the tx behavior of injected frames for these kind of
tests.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Cc: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Documentation/networking/mac80211-injection.txt

@@ -28,6 +28,23 @@ radiotap headers and used to control injection:
    IEEE80211_RADIOTAP_F_TX_NOACK: frame should be sent without waiting for
 				  an ACK even if it is a unicast frame
 
+ * IEEE80211_RADIOTAP_RATE
+
+   legacy rate for the transmission (only for devices without own rate control)
+
+ * IEEE80211_RADIOTAP_MCS
+
+   HT rate for the transmission (only for devices without own rate control).
+   Also some flags are parsed
+
+   IEEE80211_TX_RC_SHORT_GI: use short guard interval
+   IEEE80211_TX_RC_40_MHZ_WIDTH: send in HT40 mode
+
+ * IEEE80211_RADIOTAP_DATA_RETRIES
+
+   number of retries when either IEEE80211_RADIOTAP_RATE or
+   IEEE80211_RADIOTAP_MCS was used
+
 The injection code can also skip all other currently defined radiotap fields
 facilitating replay of captured radiotap headers directly.
 

include/net/mac80211.h

@@ -708,12 +708,14 @@ enum mac80211_tx_info_flags {
  *	protocol frame (e.g. EAP)
  * @IEEE80211_TX_CTRL_PS_RESPONSE: This frame is a response to a poll
  *	frame (PS-Poll or uAPSD).
+ * @IEEE80211_TX_CTRL_RATE_INJECT: This frame is injected with rate information
  *
  * These flags are used in tx_info->control.flags.
  */
 enum mac80211_tx_control_flags {
 	IEEE80211_TX_CTRL_PORT_CTRL_PROTO	= BIT(0),
 	IEEE80211_TX_CTRL_PS_RESPONSE		= BIT(1),
+	IEEE80211_TX_CTRL_RATE_INJECT		= BIT(2),
 };
 
 /*

net/mac80211/tx.c

@@ -710,6 +710,10 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)
 
 	info->control.short_preamble = txrc.short_preamble;
 
+	/* don't ask rate control when rate already injected via radiotap */
+	if (info->control.flags & IEEE80211_TX_CTRL_RATE_INJECT)
+		return TX_CONTINUE;
+
 	if (tx->sta)
 		assoc = test_sta_flag(tx->sta, WLAN_STA_ASSOC);
 
@@ -1665,15 +1669,24 @@ void ieee80211_xmit(struct ieee80211_sub_if_data *sdata,
 	ieee80211_tx(sdata, sta, skb, false);
 }
 
-static bool ieee80211_parse_tx_radiotap(struct sk_buff *skb)
+static bool ieee80211_parse_tx_radiotap(struct ieee80211_local *local,
+					struct sk_buff *skb)
 {
 	struct ieee80211_radiotap_iterator iterator;
 	struct ieee80211_radiotap_header *rthdr =
 		(struct ieee80211_radiotap_header *) skb->data;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+	struct ieee80211_supported_band *sband =
+		local->hw.wiphy->bands[info->band];
 	int ret = ieee80211_radiotap_iterator_init(&iterator, rthdr, skb->len,
 						   NULL);
 	u16 txflags;
+	u16 rate = 0;
+	bool rate_found = false;
+	u8 rate_retries = 0;
+	u16 rate_flags = 0;
+	u8 mcs_known, mcs_flags;
+	int i;
 
 	info->flags |= IEEE80211_TX_INTFL_DONT_ENCRYPT |
 		       IEEE80211_TX_CTL_DONTFRAG;
@@ -1724,6 +1737,35 @@ static bool ieee80211_parse_tx_radiotap(struct sk_buff *skb)
 				info->flags |= IEEE80211_TX_CTL_NO_ACK;
 			break;
 
+		case IEEE80211_RADIOTAP_RATE:
+			rate = *iterator.this_arg;
+			rate_flags = 0;
+			rate_found = true;
+			break;
+
+		case IEEE80211_RADIOTAP_DATA_RETRIES:
+			rate_retries = *iterator.this_arg;
+			break;
+
+		case IEEE80211_RADIOTAP_MCS:
+			mcs_known = iterator.this_arg[0];
+			mcs_flags = iterator.this_arg[1];
+			if (!(mcs_known & IEEE80211_RADIOTAP_MCS_HAVE_MCS))
+				break;
+
+			rate_found = true;
+			rate = iterator.this_arg[2];
+			rate_flags = IEEE80211_TX_RC_MCS;
+
+			if (mcs_known & IEEE80211_RADIOTAP_MCS_HAVE_GI &&
+			    mcs_flags & IEEE80211_RADIOTAP_MCS_SGI)
+				rate_flags |= IEEE80211_TX_RC_SHORT_GI;
+
+			if (mcs_known & IEEE80211_RADIOTAP_MCS_HAVE_BW &&
+			    mcs_flags & IEEE80211_RADIOTAP_MCS_BW_40)
+				rate_flags |= IEEE80211_TX_RC_40_MHZ_WIDTH;
+			break;
+
 		/*
 		 * Please update the file
 		 * Documentation/networking/mac80211-injection.txt
@@ -1738,6 +1780,32 @@ static bool ieee80211_parse_tx_radiotap(struct sk_buff *skb)
 	if (ret != -ENOENT) /* ie, if we didn't simply run out of fields */
 		return false;
 
+	if (rate_found) {
+		info->control.flags |= IEEE80211_TX_CTRL_RATE_INJECT;
+
+		for (i = 0; i < IEEE80211_TX_MAX_RATES; i++) {
+			info->control.rates[i].idx = -1;
+			info->control.rates[i].flags = 0;
+			info->control.rates[i].count = 0;
+		}
+
+		if (rate_flags & IEEE80211_TX_RC_MCS) {
+			info->control.rates[0].idx = rate;
+		} else {
+			for (i = 0; i < sband->n_bitrates; i++) {
+				if (rate * 5 != sband->bitrates[i].bitrate)
+					continue;
+
+				info->control.rates[0].idx = i;
+				break;
+			}
+		}
+
+		info->control.rates[0].flags = rate_flags;
+		info->control.rates[0].count = min_t(u8, rate_retries + 1,
+						     local->hw.max_rate_tries);
+	}
+
 	/*
 	 * remove the radiotap header
 	 * iterator->_max_length was sanity-checked against
@@ -1819,7 +1887,7 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 		      IEEE80211_TX_CTL_INJECTED;
 
 	/* process and remove the injection radiotap header */
-	if (!ieee80211_parse_tx_radiotap(skb))
+	if (!ieee80211_parse_tx_radiotap(local, skb))
 		goto fail;
 
 	rcu_read_lock();