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authorAlexander Wetzel <alexander@wetzel-home.de>2018-08-31 15:00:38 +0200
committerJohannes Berg <johannes.berg@intel.com>2018-09-05 10:03:17 +0200
commit62872a9b9a106f00360193f428451c321ec2e823 (patch)
treef5cf08ae8bc2f91e03e01365c6bad51c4bb32fe0 /net/mac80211/tx.c
parent2b815b04dfe45d1278fd4137675fe1398f656b0a (diff)
downloadlinux-62872a9b9a106f00360193f428451c321ec2e823.tar.bz2
mac80211: Fix PTK rekey freezes and clear text leak
Rekeying PTK keys without "Extended Key ID for Individually Addressed Frames" did use a procedure not suitable to replace in-use keys and could caused the following issues: 1) Freeze caused by incoming frames: If the local STA installed the key prior to the remote STA we still had the old key active in the hardware when mac80211 switched over to the new key. Therefore there was a window where the card could hand over frames decoded with the old key to mac80211 and bump the new PN (IV) value to an incorrect high number. When it happened the local replay detection silently started to drop all frames sent with the new key. 2) Freeze caused by outgoing frames: If mac80211 was providing the PN (IV) and handed over a clear text frame for encryption to the hardware prior to a key change the driver/card could have processed the queued frame after switching to the new key. This bumped the PN value on the remote STA to an incorrect high number, tricking the remote STA to discard all frames we sent later. 3) Freeze caused by RX aggregation reorder buffer: An aggregation session started with the old key and ending after the switch to the new key also bumped the PN to an incorrect high number, freezing the connection quite similar to 1). 4) Freeze caused by repeating lost frames in an aggregation session: A driver could repeat a lost frame and encrypt it with the new key while in a TX aggregation session without updating the PN for the new key. This also could freeze connections similar to 2). 5) Clear text leak: Removing encryption offload from the card cleared the encryption offload flag only after the card had deleted the key and we did not stop TX during the rekey. The driver/card could therefore get unencrypted frames from mac80211 while no longer be instructed to encrypt them. To prevent those issues the key install logic has been changed: - Mac80211 divers known to be able to rekey PTK0 keys have to set @NL80211_EXT_FEATURE_CAN_REPLACE_PTK0, - mac80211 stops queuing frames depending on the key during the replace - the key is first replaced in the hardware and after that in mac80211 - and mac80211 stops/blocks new aggregation sessions during the rekey. For drivers not setting @NL80211_EXT_FEATURE_CAN_REPLACE_PTK0 the user space must avoid PTK rekeys if "Extended Key ID for Individually Addressed Frames" is not being used. Rekeys for mac80211 drivers without this flag will generate a warning and use an extra call to ieee80211_flush_queues() to both highlight and try to prevent the issues with not updated drivers. The core of the fix changes the key install procedure from: - atomic switch over to the new key in mac80211 - remove the old key in the hardware (stops encryption offloading, fall back to software encryption with a potential clear text packet leak in between) - delete the inactive old key in mac80211 - enable hardware encryption offloading for the new key to: - if it's a PTK mark the old key as tainted to drop TX frames with the outgoing key - replace the key in hardware with the new one - atomic switch over to the new (not marked as tainted) key in mac80211 (which also resumes TX) - delete the inactive old key in mac80211 With the new sequence the hardware will be unable to decrypt frames encrypted with the old key prior to switching to the new key in mac80211 and thus prevent PNs from packets decrypted with the old key to be accounted against the new key. For that to work the drivers have to provide a clear boundary. Mac80211 drivers setting @NL80211_EXT_FEATURE_CAN_REPLACE_PTK0 confirm to provide it and mac80211 will then be able to correctly rekey in-use PTK keys with those drivers. The mac80211 requirements for drivers to set the flag have been added to the "Hardware crypto acceleration" documentation section. It drills down to: The drivers must not hand over frames decrypted with the old key to mac80211 once the call to set_key() with %DISABLE_KEY has been completed. It's allowed to either drop or continue to use the old key for any outgoing frames which are already in the queues, but it must not send out any of them unencrypted or encrypted with the new key. Even with the new boundary in place aggregation sessions with the reorder buffer are problematic: RX aggregation session started prior and completed after the rekey could still dump frames received with the old key at mac80211 after it switched over to the new key. This is side stepped by stopping all (RX and TX) aggregation sessions when replacing a PTK key and hardware key offloading. Stopping TX aggregation sessions avoids the need to get the PNs (IVs) updated in frames prepared for the old key and (re)transmitted after the switch to the new key. As a bonus it improves the compatibility when the remote STA is not handling rekeys as it should. When using software crypto aggregation sessions are not stopped. Mac80211 won't be able to decode the dangerous frames and discard them without special handling. Signed-off-by: Alexander Wetzel <alexander@wetzel-home.de> [trim overly long rekey warning] Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Diffstat (limited to 'net/mac80211/tx.c')
-rw-r--r--net/mac80211/tx.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 7d34222337c0..e88547842239 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2968,6 +2968,10 @@ void ieee80211_check_fast_xmit(struct sta_info *sta)
if (!(build.key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE))
goto out;
+ /* Key is being removed */
+ if (build.key->flags & KEY_FLAG_TAINTED)
+ goto out;
+
switch (build.key->conf.cipher) {
case WLAN_CIPHER_SUITE_CCMP:
case WLAN_CIPHER_SUITE_CCMP_256: