[PATCH 3.16.y-ckt 166/254] mac80211: fix use-after-free in defragmentation

[Luis Henriques]

3.16.7-ckt2 -stable review patch.  If anyone has any objections, please let me know.

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

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

commit b8fff407a180286aa683d543d878d98d9fc57b13 upstream.

Upon receiving the last fragment, all but the first fragment
are freed, but the multicast check for statistics at the end
of the function refers to the current skb (the last fragment)
causing a use-after-free bug.

Since multicast frames cannot be fragmented and we check for
this early in the function, just modify that check to also
do the accounting to fix the issue.

Reported-by: Yosef Khyal <yosefx.khyal at intel.com>
Signed-off-by: Johannes Berg <johannes.berg at intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/mac80211/rx.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 394e201cde6d..e3f758a14387 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1646,11 +1646,14 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
 	sc = le16_to_cpu(hdr->seq_ctrl);
 	frag = sc & IEEE80211_SCTL_FRAG;
 
-	if (likely((!ieee80211_has_morefrags(fc) && frag == 0) ||
-		   is_multicast_ether_addr(hdr->addr1))) {
-		/* not fragmented */
+	if (likely(!ieee80211_has_morefrags(fc) && frag == 0))
+		goto out;
+
+	if (is_multicast_ether_addr(hdr->addr1)) {
+		rx->local->dot11MulticastReceivedFrameCount++;
 		goto out;
 	}
+
 	I802_DEBUG_INC(rx->local->rx_handlers_fragments);
 
 	if (skb_linearize(rx->skb))
@@ -1743,10 +1746,7 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
  out:
 	if (rx->sta)
 		rx->sta->rx_packets++;
-	if (is_multicast_ether_addr(hdr->addr1))
-		rx->local->dot11MulticastReceivedFrameCount++;
-	else
-		ieee80211_led_rx(rx->local);
+	ieee80211_led_rx(rx->local);
 	return RX_CONTINUE;
 }
 
-- 
2.1.0