ath9k: Do not remove header padding on RX from short frames

The 802.11 header is only padded to 32-bit boundary when the frame has
a non-zero length payload. In other words, control frames (e.g., ACK)
do not have a padding and we should not try to remove it. This fixes
monitor mode for short control frames. In addition, the hdrlen&3 use
is described in more detail to make it easier to understand how the
padding length is calculated.

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/net/wireless/ath9k/recv.c b/drivers/net/wireless/ath9k/recv.c
index cb449f0b4171..f2327d8e9c28 100644
--- a/drivers/net/wireless/ath9k/recv.c
+++ b/drivers/net/wireless/ath9k/recv.c
@@ -571,8 +571,16 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush)
                 hdr = (struct ieee80211_hdr *)skb->data;
                 hdrlen = ieee80211_get_hdrlen_from_skb(skb);
 
-                if (hdrlen & 3) {
-                        padsize = hdrlen % 4;
+                /* 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. */
+                padsize = hdrlen & 3;
+                if (padsize && hdrlen >= 24) {
                         memmove(skb->data + padsize, skb->data, hdrlen);
                         skb_pull(skb, padsize);
                 }