[43/43] iwlwifi: fix skb usage after free

[Greg KH]

2.6.33-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>

commit b25026981aecde3685dd0e45ad980fff9f528daa upstream.

Since

commit a120e912eb51e347f36c71b60a1d13af74d30e83
Author: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Date:   Fri Feb 19 15:47:33 2010 -0800

    iwlwifi: sanity check before counting number of tfds can be free

we use skb->data after calling ieee80211_tx_status_irqsafe(), which
could free skb instantly.

On current kernels I do not observe practical problems related with
bug, but on 2.6.35.y it cause random system hangs when stressing
wireless link.

Signed-off-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Acked-by: Wey-Yi Guy <wey-yi.w.guy@xxxxxxxxx>
Signed-off-by: John W. Linville <linville@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 drivers/net/wireless/iwlwifi/iwl-tx.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/net/wireless/iwlwifi/iwl-tx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-tx.c
@@ -1162,11 +1162,15 @@ int iwl_tx_queue_reclaim(struct iwl_priv
 	     q->read_ptr = iwl_queue_inc_wrap(q->read_ptr, q->n_bd)) {
 
 		tx_info = &txq->txb[txq->q.read_ptr];
-		iwl_tx_status(priv, tx_info->skb[0]);
+
+		if (WARN_ON_ONCE(tx_info->skb == NULL))
+			continue;
 
 		hdr = (struct ieee80211_hdr *)tx_info->skb[0]->data;
-		if (hdr && ieee80211_is_data_qos(hdr->frame_control))
+		if (ieee80211_is_data_qos(hdr->frame_control))
 			nfreed++;
+
+		iwl_tx_status(priv, tx_info->skb[0]);
 		tx_info->skb[0] = NULL;
 
 		if (priv->cfg->ops->lib->txq_inval_byte_cnt_tbl)


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