mac80211: fix use-after-free

commit 8c0c709eea5cbab97fb464cd68b06f24acc58ee1
Author: Johannes Berg <johannes@sipsolutions.net>
Date:   Wed Nov 25 17:46:15 2009 +0100

    mac80211: move cmntr flag out of rx flags

moved the CMTR flag into the skb's status, and
in doing so introduced a use-after-free -- when
the skb has been handed to cooked monitors the
status setting will touch now invalid memory.

Additionally, moving it there has effectively
discarded the optimisation -- since the bit is
only ever set on freed SKBs, and those were a
copy, it could never be checked.

For the current release, fixing this properly
is a bit too involved, so let's just remove the
problematic code and leave userspace with one
copy of each frame for each virtual interface.

Cc: stable@kernel.org [2.6.33+]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index fa0f37e4afe4901226b0ccd668ae6a88c136eeb2..28624282c5f36ad5bed8f74c0e8bf7df42ee2d6c 100644 (file)
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -2199,9 +2199,6 @@ static void ieee80211_rx_cooked_monitor(struct ieee80211_rx_data *rx,
        struct net_device *prev_dev = NULL;
        struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 
-       if (status->flag & RX_FLAG_INTERNAL_CMTR)
-               goto out_free_skb;
-
        if (skb_headroom(skb) < sizeof(*rthdr) &&
            pskb_expand_head(skb, sizeof(*rthdr), 0, GFP_ATOMIC))
                goto out_free_skb;
@@ -2260,7 +2257,6 @@ static void ieee80211_rx_cooked_monitor(struct ieee80211_rx_data *rx,
        } else
                goto out_free_skb;
 
-       status->flag |= RX_FLAG_INTERNAL_CMTR;
        return;
 
  out_free_skb: