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    Subject[PATCH] [101/106] From: iwlwifi: fix skb usage after free
    Date
    2.6.35-longterm review patch.  If anyone has any objections, please let me know.

    ------------------
    Date: Wed, 20 Apr 2011 15:57:14 +0200
    Subject: iwlwifi: fix skb usage after free

    [AK: Did some changes for the backport to .35. Stanislaw, please verify
    them]

    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.

    Cc: stable@kernel.org # 2.6.32+
    Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
    Signed-off-by: Andi Kleen <ak@linux.intel.com>

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

    Index: linux-2.6.35.y/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
    ===================================================================
    --- linux-2.6.35.y.orig/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
    +++ linux-2.6.35.y/drivers/net/wireless/iwlwifi/iwl-agn-tx.c
    @@ -1141,11 +1141,14 @@ 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->skb[0]);
    +
    + if (WARN_ON_ONCE(tx_info->skb[0] == 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++;
    + iwlagn_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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