[PATCH 3.2 080/147] mac80211: accept key reinstall without changing anything

[Ben Hutchings]

3.2.95-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Johannes Berg <johannes.berg@xxxxxxxxx>

commit fdf7cb4185b60c68e1a75e61691c4afdc15dea0e upstream.

When a key is reinstalled we can reset the replay counters
etc. which can lead to nonce reuse and/or replay detection
being impossible, breaking security properties, as described
in the "KRACK attacks".

In particular, CVE-2017-13080 applies to GTK rekeying that
happened in firmware while the host is in D3, with the second
part of the attack being done after the host wakes up. In
this case, the wpa_supplicant mitigation isn't sufficient
since wpa_supplicant doesn't know the GTK material.

In case this happens, simply silently accept the new key
coming from userspace but don't take any action on it since
it's the same key; this keeps the PN replay counters intact.

Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
[bwh: Backported to 3.2:
 - Use __ieee80211_key_free() instead of ieee80211_key_free_unused()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/mac80211/key.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

--- a/net/mac80211/key.c
+++ b/net/mac80211/key.c
@@ -3,6 +3,7 @@
  * Copyright 2005-2006, Devicescape Software, Inc.
  * Copyright 2006-2007	Jiri Benc <jbenc@xxxxxxx>
  * Copyright 2007-2008	Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
+ * Copyright 2017	Intel Deutschland GmbH
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -456,9 +457,6 @@ int ieee80211_key_link(struct ieee80211_
 
 	pairwise = key->conf.flags & IEEE80211_KEY_FLAG_PAIRWISE;
 	idx = key->conf.keyidx;
-	key->local = sdata->local;
-	key->sdata = sdata;
-	key->sta = sta;
 
 	if (sta) {
 		/*
@@ -495,6 +493,21 @@ int ieee80211_key_link(struct ieee80211_
 	else
 		old_key = key_mtx_dereference(sdata->local, sdata->keys[idx]);
 
+	/*
+	 * Silently accept key re-installation without really installing the
+	 * new version of the key to avoid nonce reuse or replay issues.
+	 */
+	if (old_key && key->conf.keylen == old_key->conf.keylen &&
+	    !memcmp(key->conf.key, old_key->conf.key, key->conf.keylen)) {
+		__ieee80211_key_free(key);
+		ret = 0;
+		goto out;
+	}
+
+	key->local = sdata->local;
+	key->sdata = sdata;
+	key->sta = sta;
+
 	increment_tailroom_need_count(sdata);
 
 	__ieee80211_key_replace(sdata, sta, pairwise, old_key, key);
@@ -504,6 +517,7 @@ int ieee80211_key_link(struct ieee80211_
 
 	ret = ieee80211_key_enable_hw_accel(key);
 
+ out:
 	mutex_unlock(&sdata->local->key_mtx);
 
 	return ret;