iwlwifi: fix use after free bug for paged rx

In the paged rx patch (4854fde2), I introduced a bug that could possibly
touch an already freed page. It is fixed by avoiding the access in this
patch. I've also added some comments so that other people touching the
code won't make the same mistake. In the future, if we cannot avoid
access the page after being handled to the upper layer, we can use
get_page/put_page to handle it. For now, it's just not necessary.

It also fixed a debug message print bug reported by Stanislaw Gruszka
<sgruszka@redhat.com>.

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 14 insertions, 7 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-rx.c b/drivers/net/wireless/iwlwifi/iwl-rx.c
index cfc31ae4712b..e5339c9ad13e 100644
--- a/drivers/net/wireless/iwlwifi/iwl-rx.c
+++ b/drivers/net/wireless/iwlwifi/iwl-rx.c
@@ -241,6 +241,7 @@ void iwl_rx_allocate(struct iwl_priv *priv, gfp_t priority)
         struct iwl_rx_mem_buffer *rxb;
         struct page *page;
         unsigned long flags;
+        gfp_t gfp_mask = priority;
 
         while (1) {
                 spin_lock_irqsave(&rxq->lock, flags);
@@ -251,13 +252,13 @@ void iwl_rx_allocate(struct iwl_priv *priv, gfp_t priority)
                 spin_unlock_irqrestore(&rxq->lock, flags);
 
                 if (rxq->free_count > RX_LOW_WATERMARK)
-                        priority |= __GFP_NOWARN;
+                        gfp_mask |= __GFP_NOWARN;
 
                 if (priv->hw_params.rx_page_order > 0)
-                        priority |= __GFP_COMP;
+                        gfp_mask |= __GFP_COMP;
 
                 /* Alloc a new receive buffer */
-                page = alloc_pages(priority, priv->hw_params.rx_page_order);
+                page = alloc_pages(gfp_mask, priv->hw_params.rx_page_order);
                 if (!page) {
                         if (net_ratelimit())
                                 IWL_DEBUG_INFO(priv, "alloc_pages failed, "
@@ -922,6 +923,7 @@ static void iwl_pass_packet_to_mac80211(struct iwl_priv *priv,
 {
         struct sk_buff *skb;
         int ret = 0;
+        __le16 fc = hdr->frame_control;
 
         /* We only process data packets if the interface is open */
         if (unlikely(!priv->is_open)) {
@@ -946,9 +948,9 @@ static void iwl_pass_packet_to_mac80211(struct iwl_priv *priv,
         /* mac80211 currently doesn't support paged SKB. Convert it to
          * linear SKB for management frame and data frame requires
          * software decryption or software defragementation. */
-        if (ieee80211_is_mgmt(hdr->frame_control) ||
-            ieee80211_has_protected(hdr->frame_control) ||
-            ieee80211_has_morefrags(hdr->frame_control) ||
+        if (ieee80211_is_mgmt(fc) ||
+            ieee80211_has_protected(fc) ||
+            ieee80211_has_morefrags(fc) ||
             le16_to_cpu(hdr->seq_ctrl) & IEEE80211_SCTL_FRAG)
                 ret = skb_linearize(skb);
         else
@@ -960,7 +962,12 @@ static void iwl_pass_packet_to_mac80211(struct iwl_priv *priv,
                 goto out;
         }
 
-        iwl_update_stats(priv, false, hdr->frame_control, len);
+        /*
+         * XXX: We cannot touch the page and its virtual memory (hdr) after
+         * here. It might have already been freed by the above skb change.
+         */
+
+        iwl_update_stats(priv, false, fc, len);
         memcpy(IEEE80211_SKB_RXCB(skb), stats, sizeof(*stats));
 
         ieee80211_rx(priv->hw, skb);