Re: [PATCH RFC] mac80211: Filter scan results

[Dan Williams <dcbw@redhat.com>]

On Wed, 2009-02-04 at 16:08 +0100, Samuel Ortiz wrote:
> From: Samuel Ortiz <samuel.ortiz@intel.com>
> 
> In very dense environment, the scan result buffer can get really large, mostly
> due to the addition of proprietary IEs. iwlist fails, typically warning about:
> "print_scanning_info: Allocation failed". wpa_supplicant fails as well, after
> reallocating the scan result buffer several times, up to 132 Kbytes:
> 	[snip]
> 	Scan results did not fit - trying larger buffer (131072 bytes)
> 	ioctl[SIOCGIWSCAN]: Argument list too long
> 
> By adding a mac80211 module parameter, we can filter the scan results and keep
> only the ones userspace currently worries about, i.e. WPA1, WPA2, WMM and WPS.
> 
> To activate this feature, 1 has to be written to
> /sys/module/mac80211/parameters/ieee80211_scan_ie_filter

NAK.  Use cfg80211.  Module parameters are the wrong way to work around
API limitations; the API gets fixed or replaced instead.  Furthermore,
the stack/drivers should *NOT* be filtering scan results at all.  That's
the job of the userspace program requesting the results; otherwise
passive listeners will get only filtered results, and not the complete
scan list.

Dan

> Signed-off-by: Samuel Ortiz <samuel.ortiz@intel.com>
> ---
>  net/mac80211/ieee80211_i.h |    1 
>  net/mac80211/scan.c        |   65 ++++++++++++++++++++++++++++++---------------
>  net/mac80211/util.c        |   40 +++++++++++++++++++++++++++
>  3 files changed, 85 insertions(+), 21 deletions(-)
> 
> Index: wireless-testing/net/mac80211/scan.c
> ===================================================================
> --- wireless-testing.orig/net/mac80211/scan.c	2009-01-28 11:37:55.000000000 +0100
> +++ wireless-testing/net/mac80211/scan.c	2009-01-28 17:32:48.000000000 +0100
> @@ -31,6 +31,11 @@
>  #define IEEE80211_CHANNEL_TIME (HZ / 33)
>  #define IEEE80211_PASSIVE_CHANNEL_TIME (HZ / 5)
>  
> +static int ieee80211_scan_ie_filter;
> +module_param(ieee80211_scan_ie_filter, bool, 0644);
> +MODULE_PARM_DESC(ieee80211_scan_ie_filter,
> +		 "Filter IEs from scan results");
> +
>  void ieee80211_rx_bss_list_init(struct ieee80211_local *local)
>  {
>  	spin_lock_init(&local->bss_lock);
> @@ -725,33 +730,51 @@ static void ieee80211_scan_add_ies(struc
>  	if (bss == NULL || bss->ies == NULL)
>  		return;
>  
> -	/*
> -	 * If needed, fragment the IEs buffer (at IE boundaries) into short
> -	 * enough fragments to fit into IW_GENERIC_IE_MAX octet messages.
> -	 */
>  	pos = bss->ies;
>  	end = pos + bss->ies_len;
>  
> -	while (end - pos > IW_GENERIC_IE_MAX) {
> -		next = pos + 2 + pos[1];
> -		while (next + 2 + next[1] - pos < IW_GENERIC_IE_MAX)
> -			next = next + 2 + next[1];
> +	if (ieee80211_scan_ie_filter) {
> +		while (pos - end) {
> +			next = pos + 2 + pos[1];
> +			if (ieee80211_filter_ie(pos)) {
> +				memset(&iwe, 0, sizeof(iwe));
> +				iwe.cmd = IWEVGENIE;
> +				iwe.u.data.length = next - pos;
> +				*current_ev =
> +					iwe_stream_add_point(info, *current_ev,
> +							     end_buf, &iwe,
> +							     pos);
> +			}
> +			pos = next;
> +		}
> +	} else {
> +		/*
> +		 * If needed, fragment the IEs buffer (at IE boundaries) into
> +		 * short enough fragments to fit into IW_GENERIC_IE_MAX octet
> +		 * messages.
> +		 */
> +
> +		while (end - pos > IW_GENERIC_IE_MAX) {
> +			next = pos + 2 + pos[1];
> +			while (next + 2 + next[1] - pos < IW_GENERIC_IE_MAX)
> +				next = next + 2 + next[1];
>  
> -		memset(&iwe, 0, sizeof(iwe));
> -		iwe.cmd = IWEVGENIE;
> -		iwe.u.data.length = next - pos;
> -		*current_ev = iwe_stream_add_point(info, *current_ev,
> -						   end_buf, &iwe, pos);
> +			memset(&iwe, 0, sizeof(iwe));
> +			iwe.cmd = IWEVGENIE;
> +			iwe.u.data.length = next - pos;
> +			*current_ev = iwe_stream_add_point(info, *current_ev,
> +							   end_buf, &iwe, pos);
>  
> -		pos = next;
> -	}
> +			pos = next;
> +		}
>  
> -	if (end > pos) {
> -		memset(&iwe, 0, sizeof(iwe));
> -		iwe.cmd = IWEVGENIE;
> -		iwe.u.data.length = end - pos;
> -		*current_ev = iwe_stream_add_point(info, *current_ev,
> -						   end_buf, &iwe, pos);
> +		if (end > pos) {
> +			memset(&iwe, 0, sizeof(iwe));
> +			iwe.cmd = IWEVGENIE;
> +			iwe.u.data.length = end - pos;
> +			*current_ev = iwe_stream_add_point(info, *current_ev,
> +							   end_buf, &iwe, pos);
> +		}
>  	}
>  }
>  
> Index: wireless-testing/net/mac80211/util.c
> ===================================================================
> --- wireless-testing.orig/net/mac80211/util.c	2009-01-28 11:37:41.000000000 +0100
> +++ wireless-testing/net/mac80211/util.c	2009-01-28 15:57:03.000000000 +0100
> @@ -675,6 +675,46 @@ void ieee802_11_parse_elems(u8 *start, s
>  	}
>  }
>  
> +/*
> + * ieee80211_filter_ie() tries to keep only the relevant IEs for
> + * userspace (mostly hostap code).
> + */
> +int ieee80211_filter_ie(u8 *ie)
> +{
> +	u8 id, ie_len, *pos;
> +	u8 microsoft_oui[4] = {0x00, 0x50, 0xf2};
> +	u8 wpa2_oui[3] = {0x00, 0x0f, 0xac};
> +
> +	pos = ie;
> +	id = *pos++;
> +	ie_len = *pos++;
> +
> +	switch (id) {
> +	case WLAN_EID_RSN:
> +		/* WPA2 */
> +		if (ie_len >= 3 &&
> +		    !memcmp(pos, wpa2_oui, 3))
> +			return 1;
> +
> +		return 0;
> +
> +	case WLAN_EID_VENDOR_SPECIFIC:
> +		/* We're trying to catch WPA1, WMM and WPS IEs. */
> +		if (ie_len >= 3 &&
> +		    !memcmp(pos, microsoft_oui, 3)) {
> +			if ((pos[3] == 1) || /* WPA1 */
> +			    (pos[3] == 2) || /* WMM */
> +			    (pos[3] == 4))   /* WPS */
> +				return 1;
> +		}
> +
> +		return 0;
> +
> +	default:
> +		return 0;
> +	}
> +}
> +
>  void ieee80211_set_wmm_default(struct ieee80211_sub_if_data *sdata)
>  {
>  	struct ieee80211_local *local = sdata->local;
> Index: wireless-testing/net/mac80211/ieee80211_i.h
> ===================================================================
> --- wireless-testing.orig/net/mac80211/ieee80211_i.h	2009-01-28 11:37:41.000000000 +0100
> +++ wireless-testing/net/mac80211/ieee80211_i.h	2009-01-28 13:49:17.000000000 +0100
> @@ -1028,6 +1028,7 @@ void ieee80211_tx_skb(struct ieee80211_s
>  		      int encrypt);
>  void ieee802_11_parse_elems(u8 *start, size_t len,
>  			    struct ieee802_11_elems *elems);
> +int ieee80211_filter_ie(u8 *ie);
>  int ieee80211_set_freq(struct ieee80211_sub_if_data *sdata, int freq);
>  u32 ieee80211_mandatory_rates(struct ieee80211_local *local,
>  			      enum ieee80211_band band);