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>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index b909e4090e93..a0e00c6339ca 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;