From: Johannes Berg <johannes.berg@intel.com>
Date: Mon, 3 Nov 2014 14:29:09 +0100
Subject: [PATCH] mac80211: fix use-after-free in defragmentation

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.

Cc: stable@vger.kernel.org
Reported-by: Yosef Khyal <yosefx.khyal@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---

--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1678,11 +1678,14 @@ ieee80211_rx_h_defragment(struct ieee802
 	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))
@@ -1775,10 +1778,7 @@ ieee80211_rx_h_defragment(struct ieee802
  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;
 }