wpa_supplicant: Add wpa_blacklist_update()

This change adds the function wpa_blacklist_update(), which goes through
all blacklist entries and deletes them if their blacklist expired over
an hour ago. The purpose of this is to remove stale entries from the
blacklist which likely do not reflect the current condition of device's
network surroundings. This function is called whenever the blacklist is
polled, meaning that the caller always gets an up-to-date reflection of
the blacklist.

Another solution to clearing the blacklist that was considered was
to slowly reduce the counts of blacklist entries over time, and delete
them if the counts dropped below 0. We decided to go with the current
solution instead because an AP's "problematic" status is really a binary
thing: either the AP is no longer problematic, or it's still causing us
problems. So if we see any more problems within a reasonable amount of
time, it makes sense to just keep the blacklist where it was since the
AP is likely still undergoing the same issue. If we go a significant
amount of time (semi-arbitrarily chosen as 1 hour) without any issues
with an AP, it's reasonable to behave as if the AP is no longer
undergoing the same issue. If we see more problems at a later time, we
can start the blacklisting process fresh again, treating this as a brand
new issue.

Signed-off-by: Kevin Lund <kglund@google.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>

wpa_supplicant/blacklist.c

@@ -26,6 +26,8 @@ struct wpa_blacklist * wpa_blacklist_get(struct wpa_supplicant *wpa_s,
 	if (wpa_s == NULL || bssid == NULL)
 		return NULL;
 
+	wpa_blacklist_update(wpa_s);
+
 	e = wpa_s->blacklist;
 	while (e) {
 		if (os_memcmp(e->bssid, bssid, ETH_ALEN) == 0)
@@ -171,3 +173,42 @@ void wpa_blacklist_clear(struct wpa_supplicant *wpa_s)
 		os_free(prev);
 	}
 }
+
+
+/**
+ * wpa_blacklist_update - Update the entries in the blacklist,
+ * deleting entries that have been expired for over an hour.
+ * @wpa_s: Pointer to wpa_supplicant data
+ */
+void wpa_blacklist_update(struct wpa_supplicant *wpa_s)
+{
+	struct wpa_blacklist *e, *prev = NULL;
+	struct os_reltime now;
+
+	if (!wpa_s)
+		return;
+
+	e = wpa_s->blacklist;
+	os_get_reltime(&now);
+	while (e) {
+		if (os_reltime_expired(&now, &e->blacklist_start,
+				       e->timeout_secs + 3600)) {
+			struct wpa_blacklist *to_delete = e;
+
+			if (prev) {
+				prev->next = e->next;
+				e = prev->next;
+			} else {
+				wpa_s->blacklist = e->next;
+				e = wpa_s->blacklist;
+			}
+			wpa_printf(MSG_INFO, "Removed BSSID " MACSTR
+				   " from blacklist (expired)",
+				   MAC2STR(to_delete->bssid));
+			os_free(to_delete);
+		} else {
+			prev = e;
+			e = e->next;
+		}
+	}
+}

wpa_supplicant/blacklist.h

@@ -28,5 +28,6 @@ int wpa_blacklist_add(struct wpa_supplicant *wpa_s, const u8 *bssid);
 int wpa_blacklist_del(struct wpa_supplicant *wpa_s, const u8 *bssid);
 int wpa_blacklist_is_blacklisted(struct wpa_supplicant *wpa_s, const u8 *bssid);
 void wpa_blacklist_clear(struct wpa_supplicant *wpa_s);
+void wpa_blacklist_update(struct wpa_supplicant *wpa_s);
 
 #endif /* BLACKLIST_H */