mac80211: initialize fast-xmit 'info' later

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.

Cc: stable@vger.kernel.org
Reported-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 2c21b7039136..0d8b716e509e 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3287,7 +3287,7 @@ 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;
@@ -3351,6 +3351,7 @@ 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;