From: Stuart Henderson <stu@spacehopper.org>
Subject: Re: fix association to 11g-only APs
To: tech@openbsd.org
Date: Wed, 8 Oct 2025 13:05:40 +0100

ok sthen@ (7.8 retag candidate)

On 2025/10/08 11:49, Stefan Sperling wrote:
> When I replaced ieee80211_iserp_sta() with a check for the extended
> rates information element I wrongly assumed that this information
> element would always be present if 11g is supported. However, the
> xrates IE only appears in 11b/g mixed mode. APs which have 802.11b
> rates completely disabled can announce all rates via the regular
> rates IE and never send the xrates IE.
> 
> Ensure that we recognize such APs as 11g-capable regardless of the
> missing xrates IE. Otherwise assocation can fail due to a mismatch
> of basic rates.
> 
> Problem reported by landry@
> 
> 
> M  sys/net80211/ieee80211_node.c  |  27+  3-
> 
> 1 file changed, 27 insertions(+), 3 deletions(-)
> 
> commit - b8b7e987f417088024ed43ff3a6ae432124e0952
> commit + 6c9aaa207a9b063d2d0aeab7053af3632a5034a6
> blob - 8251692acf39a015ec12afa4f342e5518f9e42de
> blob + 7c6f51ab9831d139571c9ae2eb35c6fcfc300243
> --- sys/net80211/ieee80211_node.c
> +++ sys/net80211/ieee80211_node.c
> @@ -2625,6 +2625,28 @@ ieee80211_clear_vhtcaps(struct ieee80211_node *ni)
>  }
>  #endif
>  
> +int
> +ieee80211_node_is_11g(struct ieee80211_node *ni)
> +{
> +	struct ieee80211_rateset *rs = &ni->ni_rates;
> +	const struct ieee80211_rateset *rs_ofdm = &ieee80211_std_rateset_11a;
> +	int i, j;
> +
> +	if (!IEEE80211_IS_CHAN_2GHZ(ni->ni_chan))
> +		return 0;
> +
> +	/* 2GHz station which supports 11a OFDM rates implies 11g. */
> +	for (i = 0; i < rs->rs_nrates; i++) {
> +		for (j = 0; j < rs_ofdm->rs_nrates; j++) {
> +			if ((rs->rs_rates[i] & IEEE80211_RATE_VAL) ==
> +			    (rs_ofdm->rs_rates[j] & IEEE80211_RATE_VAL))
> +			    	return 1;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * Install received rate set information in the node's state block.
>   */
> @@ -2653,10 +2675,12 @@ ieee80211_setup_rates(struct ieee80211com *ic, struct 
>  		memcpy(rs->rs_rates + rs->rs_nrates, xrates+2, nxrates);
>  		rs->rs_nrates += nxrates;
>  
> -		/* 11g support implies ERP support */
> -		if (nxrates > 0 && IEEE80211_IS_CHAN_2GHZ(ni->ni_chan))
> -			ni->ni_flags |= IEEE80211_NODE_ERP;
>  	}
> +
> +	/* 11g support implies ERP support */
> +	if (ieee80211_node_is_11g(ni))
> +		ni->ni_flags |= IEEE80211_NODE_ERP;
> +
>  	return ieee80211_fix_rate(ic, ni, flags);
>  }
>  
>