nl80211: fix scheduled scan RSSI matchset attribute confusion

The scheduled scan matchsets were intended to be a list of filters,
with the found BSS having to pass at least one of them to be passed
to the host. When the RSSI attribute was added, however, this was
broken and currently wpa_supplicant adds that attribute in its own
matchset; however, it doesn't intend that to mean that anything
that passes the RSSI filter should be passed to the host, instead
it wants it to mean that everything needs to also have higher RSSI.

This is semantically problematic because we have a list of filters
like [ SSID1, SSID2, SSID3, RSSI ] with no real indication which
one should be OR'ed and which one AND'ed.

To fix this, move the RSSI filter attribute into each matchset. As
we need to stay backward compatible, treat a matchset with only the
RSSI attribute as a "default RSSI filter" for all other matchsets,
but only if there are other matchsets (an RSSI-only matchset by
itself is still desirable.)

To make driver implementation easier, keep a global min_rssi_thold
for the entire request as well. The only affected driver is ath6kl.

I found this when I looked into the code after Raja Mani submitted
a patch fixing the n_match_sets calculation to disregard the RSSI,
but that patch didn't address the semantic issue.

Reported-by: Raja Mani <rmani@qti.qualcomm.com>
Acked-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 61 insertions, 9 deletions

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 043bfbd..20be186 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -5467,6 +5467,7 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
 	enum ieee80211_band band;
 	size_t ie_len;
 	struct nlattr *tb[NL80211_SCHED_SCAN_MATCH_ATTR_MAX + 1];
+	s32 default_match_rssi = NL80211_SCAN_RSSI_THOLD_OFF;
 
 	if (!(rdev->wiphy.flags & WIPHY_FLAG_SUPPORTS_SCHED_SCAN) ||
 	    !rdev->ops->sched_scan_start)
@@ -5501,11 +5502,40 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
 	if (n_ssids > wiphy->max_sched_scan_ssids)
 		return -EINVAL;
 
-	if (info->attrs[NL80211_ATTR_SCHED_SCAN_MATCH])
+	/*
+	 * First, count the number of 'real' matchsets. Due to an issue with
+	 * the old implementation, matchsets containing only the RSSI attribute
+	 * (NL80211_SCHED_SCAN_MATCH_ATTR_RSSI) are considered as the 'default'
+	 * RSSI for all matchsets, rather than their own matchset for reporting
+	 * all APs with a strong RSSI. This is needed to be compatible with
+	 * older userspace that treated a matchset with only the RSSI as the
+	 * global RSSI for all other matchsets - if there are other matchsets.
+	 */
+	if (info->attrs[NL80211_ATTR_SCHED_SCAN_MATCH]) {
 		nla_for_each_nested(attr,
 				    info->attrs[NL80211_ATTR_SCHED_SCAN_MATCH],
-				    tmp)
-			n_match_sets++;
+				    tmp) {
+			struct nlattr *rssi;
+
+			err = nla_parse(tb, NL80211_SCHED_SCAN_MATCH_ATTR_MAX,
+					nla_data(attr), nla_len(attr),
+					nl80211_match_policy);
+			if (err)
+				return err;
+			/* add other standalone attributes here */
+			if (tb[NL80211_SCHED_SCAN_MATCH_ATTR_SSID]) {
+				n_match_sets++;
+				continue;
+			}
+			rssi = tb[NL80211_SCHED_SCAN_MATCH_ATTR_RSSI];
+			if (rssi)
+				default_match_rssi = nla_get_s32(rssi);
+		}
+	}
+
+	/* However, if there's no other matchset, add the RSSI one */
+	if (!n_match_sets && default_match_rssi != NL80211_SCAN_RSSI_THOLD_OFF)
+		n_match_sets = 1;
 
 	if (n_match_sets > wiphy->max_match_sets)
 		return -EINVAL;
@@ -5633,6 +5663,15 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
 				goto out_free;
 			ssid = tb[NL80211_SCHED_SCAN_MATCH_ATTR_SSID];
 			if (ssid) {
+				if (WARN_ON(i >= n_match_sets)) {
+					/* this indicates a programming error,
+					 * the loop above should have verified
+					 * things properly
+					 */
+					err = -EINVAL;
+					goto out_free;
+				}
+
 				if (nla_len(ssid) > IEEE80211_MAX_SSID_LEN) {
 					err = -EINVAL;
 					goto out_free;
@@ -5641,15 +5680,28 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
 				       nla_data(ssid), nla_len(ssid));
 				request->match_sets[i].ssid.ssid_len =
 					nla_len(ssid);
+				/* special attribute - old implemenation w/a */
+				request->match_sets[i].rssi_thold =
+					default_match_rssi;
+				rssi = tb[NL80211_SCHED_SCAN_MATCH_ATTR_RSSI];
+				if (rssi)
+					request->match_sets[i].rssi_thold =
+						nla_get_s32(rssi);
 			}
-			rssi = tb[NL80211_SCHED_SCAN_MATCH_ATTR_RSSI];
-			if (rssi)
-				request->rssi_thold = nla_get_u32(rssi);
-			else
-				request->rssi_thold =
-						   NL80211_SCAN_RSSI_THOLD_OFF;
 			i++;
 		}
+
+		/* there was no other matchset, so the RSSI one is alone */
+		if (i == 0)
+			request->match_sets[0].rssi_thold = default_match_rssi;
+
+		request->min_rssi_thold = INT_MAX;
+		for (i = 0; i < n_match_sets; i++)
+			request->min_rssi_thold =
+				min(request->match_sets[i].rssi_thold,
+				    request->min_rssi_thold);
+	} else {
+		request->min_rssi_thold = NL80211_SCAN_RSSI_THOLD_OFF;
 	}
 
 	if (info->attrs[NL80211_ATTR_IE]) {