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From 35f432a03e41d3bf08c51ede917f94e2288fbe8c Mon Sep 17 00:00:00 2001
From: Johannes Berg <johannes.berg@intel.com>
Date: Mon, 2 Jan 2017 11:19:29 +0100
Subject: [PATCH] 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>
---
net/mac80211/tx.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3297,7 +3297,7 @@ static bool ieee80211_xmit_fast(struct i
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;
@@ -3361,6 +3361,7 @@ static bool ieee80211_xmit_fast(struct i
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;
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