From a220858d30604902f650074bfac5a7598bc97ea4 Mon Sep 17 00:00:00 2001
From: Johannes Berg <johannes@sipsolutions.net>
Date: Mon, 23 Mar 2009 17:28:40 +0100
Subject: mac80211: add skb length sanity checking

We just found a bug in zd1211rw where it would reject
packets in the ->tx() method but leave them modified,
which would cause retransmit attempts with completely
bogus skbs, eventually leading to a panic due to not
having enough headroom in those.

This patch adds a sanity check to mac80211 to catch
such driver mistakes; in this case we warn and drop
the skb.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index b909e40..a0e00c6 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1089,7 +1089,7 @@ static int __ieee80211_tx(struct ieee80211_local *local,
 {
 	struct sk_buff *skb = *skbp, *next;
 	struct ieee80211_tx_info *info;
-	int ret;
+	int ret, len;
 	bool fragm = false;
 
 	local->mdev->trans_start = jiffies;
@@ -1125,7 +1125,12 @@ static int __ieee80211_tx(struct ieee80211_local *local,
 		}
 
 		next = skb->next;
+		len = skb->len;
 		ret = local->ops->tx(local_to_hw(local), skb);
+		if (WARN_ON(ret != NETDEV_TX_OK && skb->len != len)) {
+			dev_kfree_skb(skb);
+			ret = NETDEV_TX_OK;
+		}
 		if (ret != NETDEV_TX_OK)
 			return IEEE80211_TX_AGAIN;
 		*skbp = skb = next;
-- 
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