Receiver code: Some questions

Jouni Malinen j at w1.fi
Sun Mar 18 13:38:38 EDT 2007


On Mon, Mar 12, 2007 at 04:16:30PM +0100, ahuguet at cttc.es wrote:

> I was particularly interested keeping track of what was done to control
> type packets, and I've found out that it seems said function does not deal
> with them.
> 
> Specifically, surely that when:
> "if (skb->len > IEEE80211_DATA_HDR3_LEN) goto rx_dropped;"
> The control packets are dropped, for none of them has a header greater
> than 24 Bytes (==IEEE80211_DATA_HDR3_LEN)

Prism2/2.5/3 firmware does not deliver Control frames to the host, so
the driver does not receive them.

> I've tried to see where the CRC check is done, in the code, for those
> incoming packets. I've been unable to find it inside the aforementioned
> function

Firmware takes care of verifying FCS. No code is needed for this in the
driver.

> Wouldn't be any way to make HostAP "see" those incorrect datagrams, with
> wrong checksum?

If I remember correctly, station firmware can be configured to allow
frames with invalid FCS to be delivered to the host, but this may
require use of monitor mode (which does not work for normal AP/client
functionality).

-- 
Jouni Malinen                                            PGP id EFC895FA



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