From patchwork Sun Aug 5 18:31:21 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexander Wetzel X-Patchwork-Id: 10556205 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E4DA3157D for ; Sun, 5 Aug 2018 18:32:14 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id DF7A529471 for ; Sun, 5 Aug 2018 18:32:14 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D347D29484; Sun, 5 Aug 2018 18:32:14 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C721D29471 for ; Sun, 5 Aug 2018 18:32:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726647AbeHEUhi (ORCPT ); Sun, 5 Aug 2018 16:37:38 -0400 Received: from 7.mo177.mail-out.ovh.net ([46.105.61.149]:53714 "EHLO 7.mo177.mail-out.ovh.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726484AbeHEUhi (ORCPT ); Sun, 5 Aug 2018 16:37:38 -0400 Received: from player771.ha.ovh.net (unknown [10.109.159.154]) by mo177.mail-out.ovh.net (Postfix) with ESMTP id 57AF4BB11E for ; Sun, 5 Aug 2018 20:32:08 +0200 (CEST) Received: from awhome.eu (p57B7EB85.dip0.t-ipconnect.de [87.183.235.133]) (Authenticated sender: postmaster@awhome.eu) by player771.ha.ovh.net (Postfix) with ESMTPSA id 1DF76840093; Sun, 5 Aug 2018 20:32:07 +0200 (CEST) From: Alexander Wetzel DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=wetzel-home.de; s=wetzel-home; t=1533493918; bh=aO2Bamh2+Ofpjv5p4owFFlRdk7cvUPuScifUqsdOarM=; h=From:To:Cc:Subject:Date; b=Xz88AZOrdLRxgoadtqCqdu4KyiY9txHsunQpYXtGX7YjWH8DkbeBy6dw8HJ1V2dAo JuoSGKNcWhgPKzMq9mOfD+1UCCICxIC1j5f6TCqOaVNUBNJYwdVOqdGHLUmK24w8Xg GgKyWzWHvab8W2n4tKQr8/L1Cgg99O9KGNxuhiIM= To: johannes@sipsolutions.net Cc: linux-wireless@vger.kernel.org, Alexander Wetzel Subject: [PATCH v5 0/3] Fix PTK rekey freezes and cleartext leaks Date: Sun, 5 Aug 2018 20:31:21 +0200 Message-Id: <20180805183124.29921-1-alexander@wetzel-home.de> X-Mailer: git-send-email 2.18.0 X-Ovh-Tracer-Id: 4803089002708933831 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: 0 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedtiedruddttddgudeftdcutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfqggfjpdevjffgvefmvefgnecuuegrihhlohhuthemuceftddtnecu Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP This patch series addresses a long standing issue how mac80211 handles PTK rekeys. The current implementation can only work with SW crypto or by chance, e.g. if there are no frames transmitted while the STAs are rekeying or you hit just the right combination of cards/drivers. Any ongoing transmission while rekeying will very likely freeze the connection till the connection is rekeyed again or the user manually reconnects. Without any indication why, even in a kernel trace. The multiple ways how this can go wrong are outlined in the commit message from the last patch in this series, but here a short overview: The main culprit for that is encryption offloading to the card while handling the PN (IV) in mac80211 without any synchronization in between. This allows the replay detection code to account packets intended for the old key against the new one, which sets the PN to a value which was correct for the old key but will drop all packets send with a PN belonging to the new key. The solution is of course to make sure packets prepared for the old key are never checked against the PN (IV) of the new key, thus preventing the invalid carry over of the old PN value to the new key. The issue is complicated by the fact that at last some drivers do not expect to be asked to replace a key which may be actively in use for transmitting packets. Ath9k is e.g. simply removing the key and then sends out the queued packets in clear till the new key is installed. As a conclusion we therefore have to assume that all drivers which do not actively tell us that they can handle replacing an in-use key must not be asked to do so. Unfortunately the rekey decision is solely the responsibility of the userspace and when the kernel refuses to replace a key those programs are suddenly exposed to an new error condition. At least wpa_supplicant currently reacts badly to that and assumes the PSK is wrong instead of simply reconnecting when trying that. We also do not have an established way to inform the userspace that the rekey operation is not supported and it must not use it. As a way forward this patch series makes the needed changes to correctly rekey connections and allowing the userspace to check if PTK rekeys can be used at all. While enforcing this restriction would probably be ok there are some constellations where it can work. So instead of reporting an error back to the userspace we now only print out a warning and fall back to a best-we-can-do approach to maintain backward compatibility. Downside here is, that till the userspace catches up - or all drivers are supporting the new API for in-use key replaces - users may still suffer connection freezes and leak cleartext frames. But only a fraction of what it would be without this patch. It's also worth mentioning that most of the pitfalls reking a PTK key has could have been avoided if the first IEEE 802.11 standards would already have had the option introduced in the 2012 version, named "Extended Key ID for Individually Addressed Frames". This basically drills down to using key ID 0 and 1 for PTK keys (and shift GTKs to 2 and 3), allowing to rollover PTK keys the same way it has been established for GTK keys. Supporting this addition will be the ultimate solution for the issues, but since it only can be used if both sides are supporting it we still have to handle PTK keys only using the key ID 0. Here a quick overview of the patches in the series: 1) nl80211: Add ATOMIC_KEY_REPLACE API This adds support for NL80211_EXT_FEATURE_ATOMIC_KEY_REPLACE to nl80211. We expect the userspace (hostap, wpa_supplicant, iwd ...) to check this flag and only rekey a connection when this flag is present. When the flag is not set a rekey has to be "emulated" by a full de-association and a reconnect if it can't be avoided by the userspace. 2) mac80211: Define new driver callback replace_key This is just adding the new driver callback replace_key in mac80211 the last patch of the set can then use when needed. It's needed to provide a clear demarcation line between old packets which absolutely must not be send out with new key and new ones which should use the new key. By giving the driver the option to directly replace a running key with a updated one many drivers should be able to implement an atomic switch which is either using the old or the new key, avoiding the headach how to prevent some packets to be send out unencrypted. 3) mac80211: Fix PTK rekey freezes and cleartext leaks This finally changes how mac80211 handles the rekey and starts using the replace_key and sets NL80211_EXT_FEATURE_ATOMIC_KEY_REPLACE for drivers using mac80211 for it. GTK rekey is basically unchanged and only PTK rekey fixed to allow replacing the key with it while receiving and sending packets with HW encryption offloading and the races this causes to be factored in. When the driver is not supporting replace_key the code still fix the cleartext packet leak in mac80211 and stops RX and TX aggregation to prevent those to freeze the connection but besides that falls back to the old - know to be broken - sequence for backward compatibility. In that case mac80211 will print our a error message, alerting users that they still could leak clear text packets and may experience connection freezes till they either disable rekey or upgrade the userspace. (There is currently no updated userspace available.) Version history: V5 Fix PTK rekey freezes and cleartext leaks - rewritten most of the cover letter to give a better overview - Make "HW installs key prior to mac80211" the default for all key installs. (Cleaner, better understandable code.) - best-we-can-do approach for drivers not implementing replace_key which should work for many drivers. V4 Fix PTK rekey freezes and cleartext leaks - Switched over to a small patch series. - Allows insecure rekeys again for compatibility - Allows the userspace to check if rekeys are safe by extending nl80211. V3 mac80211: Fix PTK rekey freezes and cleartext leaks Updates the mac80211 API. When the driver is implementing the new callback replace_key mac80211 allows PTK rekeys. If not it returns an error on key install to the requester. V2 mac80211: Fix wlan freezes under load at rekey This fixes the issue in mac80211 only without API changes on a best-can-do approach. Drivers still can freeze the connection and if so have to be fixed. V1 mac80211: Fix wlan freezes under load at rekey Very simple approach, only fixing the freezes and using a not guaranteed to be working fallback to SW encryption. Alexander Wetzel (3): nl80211: Add ATOMIC_KEY_REPLACE API mac80211: Define new driver callback replace_key mac80211: Fix PTK rekey freezes and cleartext leaks include/net/mac80211.h | 15 ++++ include/uapi/linux/nl80211.h | 6 ++ net/mac80211/driver-ops.h | 20 ++++++ net/mac80211/key.c | 131 +++++++++++++++++++++++++++++------ net/mac80211/main.c | 5 ++ net/mac80211/trace.h | 39 +++++++++++ net/mac80211/tx.c | 4 ++ 7 files changed, 200 insertions(+), 20 deletions(-)