replace ieee80211_chan2mode() with ieee80211_node_abg_mode()

chan2mode() did not detect 11g APs properly. This can be fixed now that
we are setting the ERP flag in client mode, not only in hostap mode.
In 11g mode chan2mode() was wrongly selecting 11g mode for 11b-only peers.
The CHAN_ANYC case of chan2mode() was irrelevant for all callers.

Replace chan2mode() with node_abg_mode() which does not have these issues.

ok phessler@, mpi@

Author: stspdotname

sys/dev/ic/ath.c

@@ -1,4 +1,4 @@
-/*      $OpenBSD: ath.c,v 1.125 2023/11/10 15:51:20 bluhm Exp $  */
+/*      $OpenBSD: ath.c,v 1.126 2025/08/01 20:39:26 stsp Exp $  */
 /*	$NetBSD: ath.c,v 1.37 2004/08/18 21:59:39 dyoung Exp $	*/
 
 /*-
@@ -113,7 +113,7 @@ void	ath_rx_proc(void *, int);
 int	ath_tx_start(struct ath_softc *, struct ieee80211_node *,
 	    struct ath_buf *, struct mbuf *);
 void	ath_tx_proc(void *, int);
-int	ath_chan_set(struct ath_softc *, struct ieee80211_channel *);
+int	ath_chan_set(struct ath_softc *, struct ieee80211_node *);
 void	ath_draintxq(struct ath_softc *);
 void	ath_stoprecv(struct ath_softc *);
 int	ath_startrecv(struct ath_softc *);
@@ -675,7 +675,7 @@ ath_init1(struct ath_softc *sc)
 	 */
 	ni = ic->ic_bss;
 	ni->ni_chan = ic->ic_ibss_chan;
-	mode = ieee80211_chan2mode(ic, ni->ni_chan);
+	mode = ieee80211_node_abg_mode(ic, ni);
 	if (mode != sc->sc_curmode)
 		ath_setcurmode(sc, mode);
 	if (ic->ic_opmode != IEEE80211_M_MONITOR) {
@@ -2570,11 +2570,12 @@ ath_startrecv(struct ath_softc *sc)
  * ath_init.
  */
 int
-ath_chan_set(struct ath_softc *sc, struct ieee80211_channel *chan)
+ath_chan_set(struct ath_softc *sc, struct ieee80211_node *ni)
 {
 	struct ath_hal *ah = sc->sc_ah;
 	struct ieee80211com *ic = &sc->sc_ic;
 	struct ifnet *ifp = &ic->ic_if;
+	struct ieee80211_channel *chan = ni->ni_chan;
 
 	DPRINTF(ATH_DEBUG_ANY, ("%s: %u (%u MHz) -> %u (%u MHz)\n", __func__,
 	    ieee80211_chan2ieee(ic, ic->ic_ibss_chan),
@@ -2631,7 +2632,7 @@ ath_chan_set(struct ath_softc *sc, struct ieee80211_channel *chan)
 		 * if we're switching; e.g. 11a to 11b/g.
 		 */
 		ic->ic_ibss_chan = chan;
-		mode = ieee80211_chan2mode(ic, chan);
+		mode = ieee80211_node_abg_mode(ic, ni);
 		if (mode != sc->sc_curmode)
 			ath_setcurmode(sc, mode);
 
@@ -2775,7 +2776,7 @@ ath_newstate(struct ieee80211com *ic, enum ieee80211_state nstate, int arg)
 		return (*sc->sc_newstate)(ic, nstate, arg);
 	}
 	ni = ic->ic_bss;
-	error = ath_chan_set(sc, ni->ni_chan);
+	error = ath_chan_set(sc, ni);
 	if (error != 0)
 		goto bad;
 	rfilt = ath_calcrxfilter(sc);

sys/net80211/ieee80211.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ieee80211.c,v 1.90 2025/08/01 09:45:47 stsp Exp $	*/
+/*	$OpenBSD: ieee80211.c,v 1.91 2025/08/01 20:39:26 stsp Exp $	*/
 /*	$NetBSD: ieee80211.c,v 1.19 2004/06/06 05:45:29 dyoung Exp $	*/
 
 /*-
@@ -1173,55 +1173,6 @@ ieee80211_next_mode(struct ifnet *ifp)
 	return (ic->ic_curmode);
 }
 
-/*
- * Return the phy mode for with the specified channel so the
- * caller can select a rate set.  This is problematic and the
- * work here assumes how things work elsewhere in this code.
- *
- * Because the result of this function is ultimately used to select a
- * rate from the rate set of the returned mode, it must return one of the
- * legacy 11a/b/g modes; 11n and 11ac modes use MCS instead of rate sets.
- */
-enum ieee80211_phymode
-ieee80211_chan2mode(struct ieee80211com *ic,
-    const struct ieee80211_channel *chan)
-{
-	/*
-	 * Are we fixed in 11a/b/g mode?
-	 * NB: this assumes the channel would not be supplied to us
-	 *     unless it was already compatible with the current mode.
-	 */
-	if (ic->ic_curmode == IEEE80211_MODE_11A ||
-	    ic->ic_curmode == IEEE80211_MODE_11B ||
-	    ic->ic_curmode == IEEE80211_MODE_11G)
-		return ic->ic_curmode;
-
-	/* If no channel was provided, return the most suitable legacy mode. */
-	if (chan == IEEE80211_CHAN_ANYC) {
-		switch (ic->ic_curmode) {
-		case IEEE80211_MODE_AUTO:
-		case IEEE80211_MODE_11N:
-			if (ic->ic_modecaps & (1 << IEEE80211_MODE_11A))
-				return IEEE80211_MODE_11A;
-			if (ic->ic_modecaps & (1 << IEEE80211_MODE_11G))
-				return IEEE80211_MODE_11G;
-			return IEEE80211_MODE_11B;
-		case IEEE80211_MODE_11AC:
-			return IEEE80211_MODE_11A;
-		default:
-			return ic->ic_curmode;
-		}
-	}
-
-	/* Deduce a legacy mode based on the channel characteristics. */
-	if (IEEE80211_IS_CHAN_5GHZ(chan))
-		return IEEE80211_MODE_11A;
-	else if (chan->ic_flags & (IEEE80211_CHAN_OFDM|IEEE80211_CHAN_DYN))
-		return IEEE80211_MODE_11G;
-	else
-		return IEEE80211_MODE_11B;
-}
-
 /*
  * Convert IEEE80211 MCS index to ifmedia subtype.
  */

sys/net80211/ieee80211_input.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ieee80211_input.c,v 1.255 2025/03/22 07:24:08 kevlo Exp $	*/
+/*	$OpenBSD: ieee80211_input.c,v 1.256 2025/08/01 20:39:26 stsp Exp $	*/
 /*	$NetBSD: ieee80211_input.c,v 1.24 2004/05/31 11:12:24 dyoung Exp $	*/
 
 /*-
@@ -2671,7 +2671,7 @@ ieee80211_recv_assoc_resp(struct ieee80211com *ic, struct mbuf *m,
 	else if (ni->ni_flags & IEEE80211_NODE_HT)
 		ieee80211_setmode(ic, IEEE80211_MODE_11N);
 	else
-		ieee80211_setmode(ic, ieee80211_chan2mode(ic, ni->ni_chan));
+		ieee80211_setmode(ic, ieee80211_node_abg_mode(ic, ni));
 	/*
 	 * Reset the erp state (mostly the slot time) now that
 	 * our operating mode has been nailed down.

sys/net80211/ieee80211_node.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ieee80211_node.c,v 1.202 2025/08/01 09:13:11 stsp Exp $	*/
+/*	$OpenBSD: ieee80211_node.c,v 1.203 2025/08/01 20:39:26 stsp Exp $	*/
 /*	$NetBSD: ieee80211_node.c,v 1.14 2004/05/09 09:18:47 dyoung Exp $	*/
 
 /*-
@@ -931,8 +931,29 @@ ieee80211_create_ibss(struct ieee80211com* ic, struct ieee80211_channel *chan)
 		mode = IEEE80211_MODE_11AC;
 	else if (ic->ic_flags & IEEE80211_F_HTON)
 		mode = IEEE80211_MODE_11N;
-	else
-		mode = ieee80211_chan2mode(ic, ni->ni_chan);
+	else {
+		/* Was a specific 11a/b/g phy mode set by ifconfig? */
+		switch (IFM_MODE(ic->ic_media.ifm_cur->ifm_media)) {
+		case IFM_IEEE80211_11A:
+			mode = IEEE80211_MODE_11A;
+			break;
+		case IFM_IEEE80211_11G:
+			mode = IEEE80211_MODE_11G;
+			break;
+		case IFM_IEEE80211_11B:
+			mode = IEEE80211_MODE_11B;
+			break;
+		default: /* If we get here, our phy mode is MODE_AUTO. */
+			if (IEEE80211_IS_CHAN_5GHZ(ni->ni_chan))
+				mode = IEEE80211_MODE_11A;
+			else if ((ni->ni_chan->ic_flags &
+			    (IEEE80211_CHAN_OFDM | IEEE80211_CHAN_DYN)) != 0)
+				mode = IEEE80211_MODE_11G;
+			else
+				mode = IEEE80211_MODE_11B;
+			break;
+		}
+	}
 	ieee80211_setmode(ic, mode);
 	/* Pick an appropriate mode for supported legacy rates. */
 	if (ic->ic_curmode == IEEE80211_MODE_11AC) {
@@ -1303,7 +1324,7 @@ ieee80211_node_join_bss(struct ieee80211com *ic, struct ieee80211_node *selbs)
 	uint32_t assoc_fail = 0;
 
 	/* Reinitialize media mode and channels if needed. */
-	mode = ieee80211_chan2mode(ic, selbs->ni_chan);
+	mode = ieee80211_node_abg_mode(ic, selbs);
 	if (mode != ic->ic_curmode)
 		ieee80211_setmode(ic, mode);
 
@@ -1317,8 +1338,6 @@ ieee80211_node_join_bss(struct ieee80211com *ic, struct ieee80211_node *selbs)
 	ni = ic->ic_bss;
 	ni->ni_assoc_fail |= assoc_fail;
 
-	ic->ic_curmode = ieee80211_chan2mode(ic, ni->ni_chan);
-
 	/* Make sure we send valid rates in an association request. */
 	if (ic->ic_opmode == IEEE80211_M_STA)
 		ieee80211_fix_rate(ic, ni,
@@ -1561,7 +1580,7 @@ ieee80211_end_scan(struct ifnet *ifp)
 				ieee80211_setmode(ic, IEEE80211_MODE_11N);
 			else
 				ieee80211_setmode(ic,
-				    ieee80211_chan2mode(ic, ni->ni_chan));
+				    ieee80211_node_abg_mode(ic, ni));
 			return;
 		}
 
@@ -2641,6 +2660,40 @@ ieee80211_setup_rates(struct ieee80211com *ic, struct ieee80211_node *ni,
 	return ieee80211_fix_rate(ic, ni, flags);
 }
 
+/* 
+ * Return the 11a/b/g mode mutually supported for the given node.
+ * ni->ni_chan must be set before calling this, and ieee80211_setup_rates()
+ * should be called beforehand to properly differentiate 11b and 11g.
+ */
+enum ieee80211_phymode
+ieee80211_node_abg_mode(struct ieee80211com *ic, struct ieee80211_node *ni)
+{
+	/* Handle the case where our own phy mode was fixed by ifconfig. */
+	switch (IFM_MODE(ic->ic_media.ifm_cur->ifm_media)) {
+	case IFM_IEEE80211_11A:
+		return IEEE80211_MODE_11A; /* Peer uses 11a. */
+	case IFM_IEEE80211_11B:
+		return IEEE80211_MODE_11B; /* Peer uses 11b. */
+	case IFM_IEEE80211_11G:
+		/* Peer could be using either 11g or 11b, check below. */
+		break;
+	default:
+		break;
+	}
+
+	/* Our own phy mode is either 11G or AUTO. */
+
+	if (IEEE80211_IS_CHAN_5GHZ(ni->ni_chan))
+		return IEEE80211_MODE_11A;
+
+	if ((ni->ni_flags & IEEE80211_NODE_ERP) &&
+	    (ni->ni_chan->ic_flags &
+	    (IEEE80211_CHAN_OFDM | IEEE80211_CHAN_DYN)) != 0)
+		return IEEE80211_MODE_11G;
+
+	return IEEE80211_MODE_11B;
+}
+
 void
 ieee80211_node_trigger_addba_req(struct ieee80211_node *ni, int tid)
 {

sys/net80211/ieee80211_node.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ieee80211_node.h,v 1.96 2025/08/01 09:13:11 stsp Exp $	*/
+/*	$OpenBSD: ieee80211_node.h,v 1.97 2025/08/01 20:39:26 stsp Exp $	*/
 /*	$NetBSD: ieee80211_node.h,v 1.9 2004/04/30 22:57:32 dyoung Exp $	*/
 
 /*-
@@ -644,6 +644,8 @@ int ieee80211_setup_vhtop(struct ieee80211_node *, const uint8_t *,
     uint8_t, int);
 int ieee80211_setup_rates(struct ieee80211com *,
 	    struct ieee80211_node *, const u_int8_t *, const u_int8_t *, int);
+enum ieee80211_phymode ieee80211_node_abg_mode(struct ieee80211com *,
+	    struct ieee80211_node *);
 void ieee80211_node_trigger_addba_req(struct ieee80211_node *, int);
 void ieee80211_count_longslotsta(void *, struct ieee80211_node *);
 void ieee80211_count_nonerpsta(void *, struct ieee80211_node *);

sys/net80211/ieee80211_output.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ieee80211_output.c,v 1.141 2025/06/14 08:46:34 jsg Exp $	*/
+/*	$OpenBSD: ieee80211_output.c,v 1.142 2025/08/01 20:39:26 stsp Exp $	*/
 /*	$NetBSD: ieee80211_output.c,v 1.13 2004/05/31 11:02:55 dyoung Exp $	*/
 
 /*-
@@ -1258,7 +1258,7 @@ struct mbuf *
 ieee80211_get_probe_req(struct ieee80211com *ic, struct ieee80211_node *ni)
 {
 	const struct ieee80211_rateset *rs =
-	    &ic->ic_sup_rates[ieee80211_chan2mode(ic, ni->ni_chan)];
+	    &ic->ic_sup_rates[ieee80211_node_abg_mode(ic, ni)];
 	struct mbuf *m;
 	u_int8_t *frm;
 

sys/net80211/ieee80211_proto.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ieee80211_proto.c,v 1.109 2024/02/08 00:05:46 jsg Exp $	*/
+/*	$OpenBSD: ieee80211_proto.c,v 1.110 2025/08/01 20:39:26 stsp Exp $	*/
 /*	$NetBSD: ieee80211_proto.c,v 1.8 2004/04/30 23:58:20 dyoung Exp $	*/
 
 /*-
@@ -221,7 +221,7 @@ ieee80211_fix_rate(struct ieee80211com *ic, struct ieee80211_node *ni,
 
 	error = 0;
 	okrate = badrate = fixedrate = 0;
-	srs = &ic->ic_sup_rates[ieee80211_chan2mode(ic, ni->ni_chan)];
+	srs = &ic->ic_sup_rates[ieee80211_node_abg_mode(ic, ni)];
 	nrs = &ni->ni_rates;
 	for (i = 0; i < nrs->rs_nrates; ) {
 		ignore = 0;
@@ -1154,7 +1154,7 @@ ieee80211_newstate(struct ieee80211com *ic, enum ieee80211_state nstate,
 		IEEE80211_ADDR_COPY(ni->ni_macaddr, etherbroadcastaddr);
 		IEEE80211_ADDR_COPY(ni->ni_bssid, etherbroadcastaddr);
 		ni->ni_rates = ic->ic_sup_rates[
-			ieee80211_chan2mode(ic, ni->ni_chan)];
+		    ieee80211_node_abg_mode(ic, ni)];
 		ni->ni_associd = 0;
 		ni->ni_rstamp = 0;
 		ni->ni_rsn_supp_state = RSNA_SUPP_INITIALIZE;

sys/net80211/ieee80211_var.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ieee80211_var.h,v 1.111 2022/03/14 15:07:24 stsp Exp $	*/
+/*	$OpenBSD: ieee80211_var.h,v 1.112 2025/08/01 20:39:26 stsp Exp $	*/
 /*	$NetBSD: ieee80211_var.h,v 1.7 2004/05/06 03:07:10 dyoung Exp $	*/
 
 /*-
@@ -496,8 +496,6 @@ int	ieee80211_min_basic_rate(struct ieee80211com *);
 int	ieee80211_max_basic_rate(struct ieee80211com *);
 int	ieee80211_setmode(struct ieee80211com *, enum ieee80211_phymode);
 enum ieee80211_phymode ieee80211_next_mode(struct ifnet *);
-enum ieee80211_phymode ieee80211_chan2mode(struct ieee80211com *,
-		const struct ieee80211_channel *);
 void	ieee80211_disable_wep(struct ieee80211com *); 
 void	ieee80211_disable_rsn(struct ieee80211com *); 
 int	ieee80211_add_ess(struct ieee80211com *, struct ieee80211_join *);