iwlwifi: fix skb usage after free

BugLink: http://bugs.launchpad.net/bugs/780546

commit b25026981aecde3685dd0e45ad980fff9f528daa upstream.

Since

commit a120e912eb51e347f36c71b60a1d13af74d30e83
Author: Stanislaw Gruszka <sgruszka@redhat.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@redhat.com>
Acked-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/drivers/net/wireless/iwlwifi/iwl-agn-tx.c b/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
index 24a11b8..f5aaf31 100644 (file)
--- 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_priv *priv, int txq_id, int index)
             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)