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Date:	Thu, 05 May 2011 17:10:42 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Wey-Yi Guy <wey-yi.w.guy@...el.com>,
	"John W. Linville" <linville@...driver.com>
Subject: [patch 10/38] iwlwifi: fix skb usage after free

2.6.38-stable review patch.  If anyone has any objections, please let us know.

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

From: Stanislaw Gruszka <sgruszka@...hat.com>

commit b25026981aecde3685dd0e45ad980fff9f528daa upstream.

Since

commit a120e912eb51e347f36c71b60a1d13af74d30e83
Author: Stanislaw Gruszka <sgruszka@...hat.com>
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@...hat.com>
Acked-by: Wey-Yi Guy <wey-yi.w.guy@...el.com>
Signed-off-by: John W. Linville <linville@...driver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/net/wireless/iwlwifi/iwl-agn-tx.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
@@ -1207,12 +1207,16 @@ int iwlagn_tx_queue_reclaim(struct iwl_p
 	     q->read_ptr = iwl_queue_inc_wrap(q->read_ptr, q->n_bd)) {
 
 		tx_info = &txq->txb[txq->q.read_ptr];
-		iwlagn_tx_status(priv, tx_info,
-				 txq_id >= IWLAGN_FIRST_AMPDU_QUEUE);
+
+		if (WARN_ON_ONCE(tx_info->skb == NULL))
+			continue;
 
 		hdr = (struct ieee80211_hdr *)tx_info->skb->data;
-		if (hdr && ieee80211_is_data_qos(hdr->frame_control))
+		if (ieee80211_is_data_qos(hdr->frame_control))
 			nfreed++;
+
+		iwlagn_tx_status(priv, tx_info,
+				 txq_id >= IWLAGN_FIRST_AMPDU_QUEUE);
 		tx_info->skb = NULL;
 
 		if (priv->cfg->ops->lib->txq_inval_byte_cnt_tbl)


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