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bcbc9b1e89
In 2009 OpenWrt's hostapd config added an "auth_cache" boolean to be used to address a reported issue #12129 [0] on a forum [1]. The reported issue on the ticket is different that the one described on the forum. The commit was r33359. This change broke proper RSN preauthentication [2] [3] [4] expectations on hostapd's configuration for WPA2 and this in turn disabled PMKSA caching and Opportunistic Key Caching. This change: * Leaves the "auth_cache" to be used only for WPA networks for those looking to use this as a workaround to a reported issue but annotates a warning over its usage. * Separate "auth_cache" from WPA2 RSN preauthentication, leaving WPA2 RSN preauthentication to enabled only with "rsn_preauth" with the expected and recommended settings. * Adds a new WPA2 RSN preauthentication "rsn_preauth_testing" to be used when evaluating funcionality for WPA2 RSN preauthentication with the expected and recommended settings with the only difference so far with what should be enabled by default to disable Opportunistic Key Caching. Disabling the PMKSA cache should mean the STA could not roam off and back onto the AP that had PMKSA caching disabled and would require a full authentication cycle. This fixes this for WPA2 networks with RSN preauthentication enabled. This change should be applied to AA as well as trunk. TL DR; The issue described on the forum has to do with failure of a STA being able to try to authenticate again with the AP if it failed its first try. This may have been an issue with hostapd in 2009 but as per some tests I cannot reproduce this today on a WPA2 network. The issue described on the ticket alludes to a security issue with the design of using a Radius server to authenticate to an AP. The issue vaguely alludes to the circumstances of zapping a user, deleting their authentication credentials to log in to the network, and that if RSN preauthentication is enabled with PMKSA caching that the user that was zapped would still be able to authenticate. Lets treat these as separate issues. I cannot reproduce the first issue reported on the forums of not being able to authenticate anymore on a WPA2 network. The issue reported on the ticket modified WPA2 RSN preauthentication by adding two fields to the hostapd configuration if auth_cache was enabled: * disable_pmksa_caching=1 * okc=0 The first one disables PMKSA authentication cache. The second one disables Opportunistic Key Caching. The issue reported on the ticket was fixed by implementing a workaround in hostapd's configuration. Disabling PMKSA caching breaks proper use of WPA2 RSN pre authentication. The usage of disable_pmksa_caching=1 prevents hostapd from adding PMKSA entries into its cache when a successful 802.1x authentication occurs. In practice RSN preauthentication would trigger a STA to perform authentication with other APs on the same SSID, it would then have its own supplicant PMKSA cache held. If a STA roams between one AP to another no new authenitcation would need to be performed as the new AP would already have authenticated the STA. The purpose of the PMKSA cache on the AP side would be for the AP to use the same PMKID for a STA when the STA roams off onto another BSSID and later comes back to it. Disabling Opportunistic Key Caching could help the reported issue as well but its not the correct place to address this. Opportunistic Key Caching enables an AP with different interfaces to share the PMKSA cache. Its a technical enhancement and disabling it would be useful to let a testing suite properly test for RSN preauthentication given that otherwise Opportunistic Key Caching would enable an interface being tested to derive its own derive the PMKSA entry. In production though okc=1 should be enabled to help with RSN preauthentication. The real fix for this particular issue outside of the scope of hostapd's configuration and it should not be dealt with as a workaround to its configuration and breaking expected RSN preauthentication and technical optimizations. Revert this change and enable users to pick and choose to enable or disable disable_pmksa_caching and okc expecting them to instead have read clearly more what these do. As for the core issure ported, the correct place to fix this is to enable a sort of messaging between the RADIUS server and its peers so that if caching for authentication is enabled that cache can be cleared upon user credential updates. Updating a user password (not just zapping a user) is another possible issue that would need to be resolved here. Another part of the solution might be to reduce the cache timing to account for any systematic limitations (RADIUS server not able to ask peers to clear cache might be one). [0] https://dev.openwrt.org/changeset/33359 [1] https://forum.openwrt.org/viewtopic.php?id=19596 [2] http://wireless.kernel.org/en/users/Documentation/hostapd#IEEE_802.11i.2FRSN.2FWPA2_pre-authentication [3] http://wireless.kernel.org/en/users/Documentation/wpa_supplicant#RSN_preauthentication [4] http://wiki.openwrt.org/doc/recipes/rsn_preauthentication Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com> SVN-Revision: 38336 |
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