linux-kernel - [PATCH 3.2 108/164] mac80211: fix use-after-free in defragmentation

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Date:	Fri, 12 Dec 2014 06:14:25 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Yosef Khyal" <yosefx.khyal@...el.com>,
	"Johannes Berg" <johannes.berg@...el.com>
Subject: [PATCH 3.2 108/164] mac80211: fix use-after-free in defragmentation

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

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

From: Johannes Berg <johannes.berg@...el.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@...el.com>
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/mac80211/rx.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1470,11 +1470,14 @@ 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))
@@ -1567,10 +1570,7 @@ 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;
 }
 

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