mac80211: initialize fast-xmit 'info' later

commit 35f432a03e41d3bf08c51ede917f94e2288fbe8c upstream.

In ieee80211_xmit_fast(), 'info' is initialized to point to the skb
that's passed in, but that skb may later be replaced by a clone (if
it was shared), leading to an invalid pointer.

This can lead to use-after-free and also later crashes since the
real SKB's info->hw_queue doesn't get initialized properly.

Fix this by assigning info only later, when it's needed, after the
skb replacement (may have) happened.

Reported-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index e1225b395415efb457269d8a11740be273efbfd3..ea5dfefd765ad55c88ee1f42d8e58fad2920ae8a 100644 (file)
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2699,7 +2699,7 @@ static bool ieee80211_xmit_fast(struct ieee80211_sub_if_data *sdata,
        int extra_head = fast_tx->hdr_len - (ETH_HLEN - 2);
        int hw_headroom = sdata->local->hw.extra_tx_headroom;
        struct ethhdr eth;
-       struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+       struct ieee80211_tx_info *info;
        struct ieee80211_hdr *hdr = (void *)fast_tx->hdr;
        struct ieee80211_tx_data tx;
        ieee80211_tx_result r;
@@ -2761,6 +2761,7 @@ static bool ieee80211_xmit_fast(struct ieee80211_sub_if_data *sdata,
        memcpy(skb->data + fast_tx->da_offs, eth.h_dest, ETH_ALEN);
        memcpy(skb->data + fast_tx->sa_offs, eth.h_source, ETH_ALEN);
 
+       info = IEEE80211_SKB_CB(skb);
        memset(info, 0, sizeof(*info));
        info->band = fast_tx->band;
        info->control.vif = &sdata->vif;