[PATCH] mac80211: check PN correctly for GCMP-encrypted fragmented MPDUs

[PATCH] mac80211: check PN correctly for GCMP-encrypted fragmented MPDUs

[Johannes Berg]

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

Just like for CCMP we need to check that for GCMP the fragments
have PNs that increment by one; the spec was updated to fix this
security issue and now has the following text:

	The receiver shall discard MSDUs and MMPDUs whose constituent
	MPDU PN values are not incrementing in steps of 1.

Adapt the code for CCMP to work for GCMP as well, luckily the
relevant fields already alias each other so no code duplication
is needed (just check the aliasing with BUILD_BUG_ON.)

Cc: stable@vger.kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 net/mac80211/ieee80211_i.h |  2 +-
 net/mac80211/rx.c          | 36 +++++++++++++++++++++++++++---------
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 1630975c89f1..804575ff7af5 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -92,7 +92,7 @@ struct ieee80211_fragment_entry {
 	u16 extra_len;
 	u16 last_frag;
 	u8 rx_queue;
-	bool ccmp; /* Whether fragments were encrypted with CCMP */
+	bool check_sequential_pn; /* needed for CCMP/GCMP */
 	u8 last_pn[6]; /* PN of the last fragment if CCMP was used */
 };
 
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 91279576f4a7..853c71766241 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1777,7 +1777,7 @@ ieee80211_reassemble_add(struct ieee80211_sub_if_data *sdata,
 	entry->seq = seq;
 	entry->rx_queue = rx_queue;
 	entry->last_frag = frag;
-	entry->ccmp = 0;
+	entry->check_sequential_pn = false;
 	entry->extra_len = 0;
 
 	return entry;
@@ -1873,15 +1873,27 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
 						 rx->seqno_idx, &(rx->skb));
 		if (rx->key &&
 		    (rx->key->conf.cipher == WLAN_CIPHER_SUITE_CCMP ||
-		     rx->key->conf.cipher == WLAN_CIPHER_SUITE_CCMP_256) &&
+		     rx->key->conf.cipher == WLAN_CIPHER_SUITE_CCMP_256 ||
+		     rx->key->conf.cipher == WLAN_CIPHER_SUITE_GCMP ||
+		     rx->key->conf.cipher == WLAN_CIPHER_SUITE_GCMP_256) &&
 		    ieee80211_has_protected(fc)) {
 			int queue = rx->security_idx;
-			/* Store CCMP PN so that we can verify that the next
-			 * fragment has a sequential PN value. */
-			entry->ccmp = 1;
+
+			/* Store CCMP/GCMP PN so that we can verify that the
+			 * next fragment has a sequential PN value.
+			 */
+			entry->check_sequential_pn = true;
 			memcpy(entry->last_pn,
 			       rx->key->u.ccmp.rx_pn[queue],
 			       IEEE80211_CCMP_PN_LEN);
+			BUILD_BUG_ON(offsetof(struct ieee80211_key,
+					      u.ccmp.rx_pn) !=
+				     offsetof(struct ieee80211_key,
+					      u.gcmp.rx_pn));
+			BUILD_BUG_ON(sizeof(rx->key->u.ccmp.rx_pn[queue]) !=
+				     sizeof(rx->key->u.gcmp.rx_pn[queue]));
+			BUILD_BUG_ON(IEEE80211_CCMP_PN_LEN !=
+				     IEEE80211_GCMP_PN_LEN);
 		}
 		return RX_QUEUED;
 	}
@@ -1896,15 +1908,21 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
 		return RX_DROP_MONITOR;
 	}
 
-	/* Verify that MPDUs within one MSDU have sequential PN values.
-	 * (IEEE 802.11i, 8.3.3.4.5) */
-	if (entry->ccmp) {
+	/* "The receiver shall discard MSDUs and MMPDUs whose constituent
+	 *  MPDU PN values are not incrementing in steps of 1."
+	 * see IEEE P802.11-REVmc/D5.0, 12.5.3.4.4, item d (for CCMP)
+	 * and IEEE P802.11-REVmc/D5.0, 12.5.5.4.4, item d (for GCMP)
+	 */
+	if (entry->check_sequential_pn) {
 		int i;
 		u8 pn[IEEE80211_CCMP_PN_LEN], *rpn;
 		int queue;
+
 		if (!rx->key ||
 		    (rx->key->conf.cipher != WLAN_CIPHER_SUITE_CCMP &&
-		     rx->key->conf.cipher != WLAN_CIPHER_SUITE_CCMP_256))
+		     rx->key->conf.cipher != WLAN_CIPHER_SUITE_CCMP_256 &&
+		     rx->key->conf.cipher != WLAN_CIPHER_SUITE_GCMP &&
+		     rx->key->conf.cipher != WLAN_CIPHER_SUITE_GCMP_256))
 			return RX_DROP_UNUSABLE;
 		memcpy(pn, entry->last_pn, IEEE80211_CCMP_PN_LEN);
 		for (i = IEEE80211_CCMP_PN_LEN - 1; i >= 0; i--) {
-- 
2.7.0

Re: [PATCH] mac80211: check PN correctly for GCMP-encrypted fragmented MPDUs

[Johannes Berg]

On Fri, 2016-02-26 at 22:16 +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
> 
> Just like for CCMP we need to check that for GCMP the fragments
> have PNs that increment by one; the spec was updated to fix this
> security issue and now has the following text:
> 
> 	The receiver shall discard MSDUs and MMPDUs whose constituent
> 	MPDU PN values are not incrementing in steps of 1.
> 
> Adapt the code for CCMP to work for GCMP as well, luckily the
> relevant fields already alias each other so no code duplication
> is needed (just check the aliasing with BUILD_BUG_ON.)
> 
Applied.

johannes