Re: [B.A.T.M.A.N.] [PATCH] batctl: add raw wifi packet decapsulation support

Sven Eckelmann
2011-01-26T15:02:32Z

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On Wednesday 26 January 2011 15:30:08 Marek Lindner wrote:
> Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
> ---
> + buff_len -= PRISM_HEADER_LEN;
> + packet_buff += PRISM_HEADER_LEN;
> +
> + /* we assume a minimum size of 38 bytes
> + * (802.11 data frame + LLC)
> + * before we calculate the real size */
> + if (buff_len <= 38)
> + return;
> +
> + wifi_hdr = (struct ieee80211_hdr *)packet_buff;
> + fc = wifi_hdr->frame_control;
> +
> + /* not carrying payload */
> + if ((fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA)
> + return;

Didn't we say yesterday that we must either use ntohs or only read the first
byte of the framecontrol? The last option which comes to my mind is to define
IEEE80211_FCTL_FTYPE and IEEE80211_FTYPE_DATA for big and little endian
independently.

The same for
IEEE80211_FCTL_TODS 0x0100
IEEE80211_FCTL_FROMDS 0x0200
IEEE80211_FCTL_PROTECTED 0x4000
IEEE80211_STYPE_QOS_DATA 0x0080

Your current version should only work on little endian systems. I would
suggest following version:

#define IEEE80211_FCTL_FTYPE 0x0c00
#define IEEE80211_FTYPE_DATA 0x0800
#define IEEE80211_FCTL_TODS 0x0001
#define IEEE80211_FCTL_FROMDS 0x0002
#define IEEE80211_FCTL_PROTECTED 0x0040
#define IEEE80211_STYPE_QOS_DATA 0x8000

fc = ntohs(wifi_hdr->frame_control);

> + if (fc & IEEE80211_STYPE_QOS_DATA)
> + hdr_len += 2;

Here are you testing only on bit. Are you sure that the other 3 bits aren't
interesting? At least one combination isn't well defined by the 802.11
standard from 2007 and some others are null data types.

Best regards,
Sven

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