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

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

[Jouni Malinen]

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>

---
 drivers/net/wireless/ath9k/recv.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- wireless-testing.orig/drivers/net/wireless/ath9k/recv.c	2008-12-11 11:35:56.000000000 +0200
+++ wireless-testing/drivers/net/wireless/ath9k/recv.c	2008-12-11 12:18:02.000000000 +0200
@@ -571,8 +571,16 @@ int ath_rx_tasklet(struct ath_softc *sc,
 		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);
 		}

-- 
Jouni Malinen                                            PGP id EFC895FA

Re: [PATCH] ath9k: Do not remove header padding on RX from short frames

[Bob Copeland]

On Thu, Dec 11, 2008 at 11:22 AM, Jouni Malinen
<jouni.malinen@atheros.com> wrote:
> 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.

Thanks Jouni, that clears up the question of the same code in ath5k
(http://marc.info/?l=linux-wireless&m=122888546315200&w=2).

-- 
Bob Copeland %% www.bobcopeland.com

Re: [PATCH] ath9k: Do not remove header padding on RX from short frames

[Jouni Malinen]

On Thu, 2008-12-11 at 11:49 -0800, Bob Copeland wrote:
> On Thu, Dec 11, 2008 at 11:22 AM, Jouni Malinen
> <jouni.malinen@atheros.com> wrote:
> > The 802.11 header is only padded to 32-bit boundary when the frame has
> > a non-zero length payload.

> Thanks Jouni, that clears up the question of the same code in ath5k
> (http://marc.info/?l=linux-wireless&m=122888546315200&w=2).

Yes, the same rules on 802.11 header padding applies to ath5k.

- Jouni

Re: [PATCH] ath9k: Do not remove header padding on RX from short frames

[Senthil Balasubramanian]

On Thu, Dec 11, 2008 at 09:52:13PM +0530, Jouni Malinen wrote:
> 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>
> 
> ---
>  drivers/net/wireless/ath9k/recv.c |   12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> --- wireless-testing.orig/drivers/net/wireless/ath9k/recv.c     2008-12-11 11:35:56.000000000 +0200
> +++ wireless-testing/drivers/net/wireless/ath9k/recv.c  2008-12-11 12:18:02.000000000 +0200
> @@ -571,8 +571,16 @@ int ath_rx_tasklet(struct ath_softc *sc,
>                 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) {
I think "if(padsize && hdrlen > 24)" should be sufficient here as padsize is
anyway zero for hdlen==24.
>                         memmove(skb->data + padsize, skb->data, hdrlen);
>                         skb_pull(skb, padsize);
>                 }
> 
> --
> Jouni Malinen                                            PGP id EFC895FA
> --
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