ath5k: fix 802.11 header padding on RX, unpadding on TX

Padding the 802.11 header to a multiple of 4 bytes needs to be done only for
frames with a body. This fixes a bug where 2 bytes were missing in monitor
mode for ACK frames. Inspired by a patch from Jouni Malinen on ath9k.

Ref: http://bugzilla.kernel.org/show_bug.cgi?id=12101 :
Signed-off-by: Benoit Papillault <benoit.papillault@free.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 21 insertions, 17 deletions

diff --git a/drivers/net/wireless/ath5k/base.c b/drivers/net/wireless/ath5k/base.c
index 0e4317010ed0..9b5f31aab574 100644
--- a/drivers/net/wireless/ath5k/base.c
+++ b/drivers/net/wireless/ath5k/base.c
@@ -1668,7 +1668,7 @@ ath5k_tasklet_rx(unsigned long data)
         struct ath5k_desc *ds;
         int ret;
         int hdrlen;
-        int pad;
+        int padsize;
 
         spin_lock(&sc->rxbuflock);
         if (list_empty(&sc->rxbuf)) {
@@ -1753,16 +1753,19 @@ accept:
 
                 skb_put(skb, rs.rs_datalen);
 
-                /*
-                 * the hardware adds a padding to 4 byte boundaries between
-                 * the header and the payload data if the header length is
-                 * not multiples of 4 - remove it
-                 */
+                /* The MAC header is padded to have 32-bit boundary if the
+                 * packet payload is non-zero. The general calculation for
+                 * padsize would take into account odd header lengths:
+                 * padsize = (4 - hdrlen % 4) % 4; However, since only
+                 * even-length headers are used, padding can only be 0 or 2
+                 * bytes and we can optimize this a bit. In addition, we must
+                 * not try to remove padding from short control frames that do
+                 * not have payload. */
                 hdrlen = ieee80211_get_hdrlen_from_skb(skb);
-                if (hdrlen & 3) {
-                        pad = hdrlen % 4;
-                        memmove(skb->data + pad, skb->data, hdrlen);
-                        skb_pull(skb, pad);
+                padsize = hdrlen & 3;
+                if (padsize && hdrlen >= 24) {
+                        memmove(skb->data + padsize, skb->data, hdrlen);
+                        skb_pull(skb, padsize);
                 }
 
                 /*
@@ -2623,7 +2626,7 @@ ath5k_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
         struct ath5k_buf *bf;
         unsigned long flags;
         int hdrlen;
-        int pad;
+        int padsize;
 
         ath5k_debug_dump_skb(sc, skb, "TX  ", 1);
 
@@ -2635,15 +2638,16 @@ ath5k_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
          * if this is not the case we add the padding after the header
          */
         hdrlen = ieee80211_get_hdrlen_from_skb(skb);
-        if (hdrlen & 3) {
-                pad = hdrlen % 4;
-                if (skb_headroom(skb) < pad) {
+        padsize = hdrlen & 3;
+        if (padsize && hdrlen >= 24) {
+
+                if (skb_headroom(skb) < padsize) {
                         ATH5K_ERR(sc, "tx hdrlen not %%4: %d not enough"
-                                " headroom to pad %d\n", hdrlen, pad);
+                                  " headroom to pad %d\n", hdrlen, padsize);
                         return -1;
                 }
-                skb_push(skb, pad);
-                memmove(skb->data, skb->data+pad, hdrlen);
+                skb_push(skb, padsize);
+                memmove(skb->data, skb->data+padsize, hdrlen);
         }
 
         spin_lock_irqsave(&sc->txbuflock, flags);