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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>
This commit is contained in:
Johannes Berg 2017-01-02 11:19:29 +01:00
parent eb7903bb83
commit 35f432a03e
1 changed files with 2 additions and 1 deletions
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3
net/mac80211/tx.c
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@ -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;