wpa_supplicant: Implement time-based blacklisting
wpa_supplicant keeps a blacklist of BSSs in order to prevent repeated associations to problematic APs*. Currently, this blacklist is completely cleared whenever we successfully connect to any AP. This causes problematic behavior when in the presence of both a bad AP and a good AP. The device can repeatedly attempt to roam to the bad AP because it is clearing the blacklist every time it connects to the good AP. This results in the connection constantly ping-ponging between the APs, leaving the user stuck without connection. Instead of clearing the blacklist, implement timeout functionality which allows association attempts to blacklisted APs after some time has passed. Each time a BSS would be added to the blacklist, increase the duration of this timeout exponentially, up to a cap of 1800 seconds. This means that the device will no longer be able to immediately attempt to roam back to a bad AP whenever it successfully connects to any other AP. Other details: The algorithm for building up the blacklist count and timeout duration on a given AP has been designed to be minimally obtrusive. Starting with a fresh blacklist, the device may attempt to connect to a problematic AP no more than 6 times in any ~45 minute period. Once an AP has reached a blacklist count >= 6, the device may attempt to connect to it no more than once every 30 minutes. The goal of these limits is to find an ideal balance between minimizing connection attempts to bad APs while still trying them out occasionally to see if the problems have stopped. The only exception to the above limits is that the blacklist is still completely cleared whenever there are no APs available in a scan. This means that if all nearby APs have been blacklisted, all APs will be completely exonerated regardless of their blacklist counts or how close their blacklist entries are to expiring. When all nearby APs have been blacklisted we know that every nearby AP is in some way problematic. Once we know that every AP is causing problems, it doesn't really make sense to sort them beyond that because the blacklist count and timeout duration don't necessarily reflect the degree to which an AP is problematic (i.e. they can be manipulated by external factors such as the user physically moving around). Instead, its best to restart the blacklist and let the normal roaming algorithm take over to maximize our chance of getting the best possible connection quality. As stated above, the time-based blacklisting algorithm is designed to be minimally obtrusive to user experience, so occasionally restarting the process is not too impactful on the user. *problematic AP: rejects new clients, frequently de-auths clients, very poor connection quality, etc. Signed-off-by: Kevin Lund <kglund@google.com> Signed-off-by: Brian Norris <briannorris@chromium.org>master
Kevin Lund
4 years ago
committed by
Jouni Malinen
parent
2fd35d9857
commit
d530110028
Loading…
Reference in New Issue