linux-kernel - [PATCH 3.16 128/133] mac80211: don't compare TKIP TX MIC key in reinstall prevention

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Message-ID: <lsq.1511315893.335020416@decadent.org.uk>
Date:   Wed, 22 Nov 2017 01:58:13 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Johannes Berg" <johannes.berg@...el.com>
Subject: [PATCH 3.16 128/133] mac80211: don't compare TKIP TX MIC key in
 reinstall prevention

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

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

From: Johannes Berg <johannes.berg@...el.com>

commit cfbb0d90a7abb289edc91833d0905931f8805f12 upstream.

For the reinstall prevention, the code I had added compares the
whole key. It turns out though that iwlwifi firmware doesn't
provide the TKIP TX MIC key as it's not needed in client mode,
and thus the comparison will always return false.

For client mode, thus always zero out the TX MIC key part before
doing the comparison in order to avoid accepting the reinstall
of the key with identical encryption and RX MIC key, but not the
same TX MIC key (since the supplicant provides the real one.)

Fixes: fdf7cb4185b6 ("mac80211: accept key reinstall without changing anything")
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/mac80211/key.c | 36 ++++++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

--- a/net/mac80211/key.c
+++ b/net/mac80211/key.c
@@ -475,6 +475,39 @@ void ieee80211_key_free_unused(struct ie
 	ieee80211_key_free_common(key);
 }
 
+static bool ieee80211_key_identical(struct ieee80211_sub_if_data *sdata,
+				    struct ieee80211_key *old,
+				    struct ieee80211_key *new)
+{
+	u8 tkip_old[WLAN_KEY_LEN_TKIP], tkip_new[WLAN_KEY_LEN_TKIP];
+	u8 *tk_old, *tk_new;
+
+	if (!old || new->conf.keylen != old->conf.keylen)
+		return false;
+
+	tk_old = old->conf.key;
+	tk_new = new->conf.key;
+
+	/*
+	 * In station mode, don't compare the TX MIC key, as it's never used
+	 * and offloaded rekeying may not care to send it to the host. This
+	 * is the case in iwlwifi, for example.
+	 */
+	if (sdata->vif.type == NL80211_IFTYPE_STATION &&
+	    new->conf.cipher == WLAN_CIPHER_SUITE_TKIP &&
+	    new->conf.keylen == WLAN_KEY_LEN_TKIP &&
+	    !(new->conf.flags & IEEE80211_KEY_FLAG_PAIRWISE)) {
+		memcpy(tkip_old, tk_old, WLAN_KEY_LEN_TKIP);
+		memcpy(tkip_new, tk_new, WLAN_KEY_LEN_TKIP);
+		memset(tkip_old + NL80211_TKIP_DATA_OFFSET_TX_MIC_KEY, 0, 8);
+		memset(tkip_new + NL80211_TKIP_DATA_OFFSET_TX_MIC_KEY, 0, 8);
+		tk_old = tkip_old;
+		tk_new = tkip_new;
+	}
+
+	return !crypto_memneq(tk_old, tk_new, new->conf.keylen);
+}
+
 int ieee80211_key_link(struct ieee80211_key *key,
 		       struct ieee80211_sub_if_data *sdata,
 		       struct sta_info *sta)
@@ -503,8 +536,7 @@ int ieee80211_key_link(struct ieee80211_
 	 * 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 &&
-	    !crypto_memneq(key->conf.key, old_key->conf.key, key->conf.keylen)) {
+	if (ieee80211_key_identical(sdata, old_key, key)) {
 		ieee80211_key_free_unused(key);
 		ret = 0;
 		goto out;