From: Peter Hessler <phessler@theapt.org>
Subject: Re: fix 802.11 mode selection in ieee80211_node_join_bss()
To: tech@openbsd.org
Date: Fri, 25 Jul 2025 12:24:40 +0200

On 2025 Jul 25 (Fri) at 11:34:42 +0200 (+0200), Stefan Sperling wrote:
:On Fri, Jul 25, 2025 at 11:19:16AM +0200, Stefan Sperling wrote:
:> When we are joining a new BSS (i.e. a new access point) while roaming,
:> we might have to switch bands from 2 GHz to 5 GHz or vice-versa.
:> @@ -1303,7 +1303,13 @@ ieee80211_node_join_bss(struct ieee80211com *ic, struc
:>  	uint32_t assoc_fail = 0;
:>  
:>  	/* Reinitialize media mode and channels if needed. */
:> -	mode = ieee80211_chan2mode(ic, selbs->ni_chan);
:> +	if (IEEE80211_IS_CHAN_5GHZ(selbs->ni_chan))
:> +		mode = IEEE80211_MODE_11A;
:> +	else if (ieee80211_iserp_sta(selbs))
:> +		mode = IEEE80211_MODE_11G;
:> +	else
:> +		mode = IEEE80211_MODE_11B;
:> +
:
:Ooops, this layer needs to take into account whether the driver supports 11g.
:
:Drivers announce what they support by setting appropriate channel flags.
:Check those as well to avoid breaking 11b-only devices such as atw(4). 
:

OK


:M  sys/net80211/ieee80211_node.c  |  9+  3-
:
:1 file changed, 9 insertions(+), 3 deletions(-)
:
:commit - d64e5fcced832f2a47ed1896e35987cba9887e42
:commit + bccdbcb2d328be6d1547cc7b82972e40e32611a7
:blob - c6ca10f5df7c13a01d8cddd8f552e3abf2b41184
:blob + 491e5ef044a00ce6912c53914f5f114e1473e2c6
:--- sys/net80211/ieee80211_node.c
:+++ sys/net80211/ieee80211_node.c
:@@ -1303,7 +1303,15 @@ ieee80211_node_join_bss(struct ieee80211com *ic, struc
: 	uint32_t assoc_fail = 0;
: 
: 	/* Reinitialize media mode and channels if needed. */
:-	mode = ieee80211_chan2mode(ic, selbs->ni_chan);
:+	if (IEEE80211_IS_CHAN_5GHZ(selbs->ni_chan))
:+		mode = IEEE80211_MODE_11A;
:+	else if (ieee80211_iserp_sta(selbs) &&
:+	    ((selbs->ni_chan->ic_flags &
:+	    (IEEE80211_CHAN_OFDM | IEEE80211_CHAN_DYN)) != 0))
:+		mode = IEEE80211_MODE_11G;
:+	else
:+		mode = IEEE80211_MODE_11B;
:+
: 	if (mode != ic->ic_curmode)
: 		ieee80211_setmode(ic, mode);
: 
:@@ -1317,8 +1325,6 @@ ieee80211_node_join_bss(struct ieee80211com *ic, struc
: 	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,
:

-- 
Radioactive cats have 18 half-lives.