---- On Wed, 04 Apr 2018 21:14:56 +0100 Peter J. Philipp <tcpd...@centroid.eu>
wrote ----
> Hi,
>
> I get a totally bogus output with -e and -X flags set on a wlan0
> interface in monitor mode. I have spent a lot of time looking into this
> and I have finally figured out what I needed to do here. Last I'll
> paste my patch, it's easy. I know it isn't via github but I don't have
> a github login and can't even write an issue wihtout having logged in,
> so I resorted to this sane historical way.
Hello Peter.
Thank you for sending the proposed bug fix. If it requires a specific 802.11
frame to reproduce, could you post a sample .pcap file?
> I want to show you the outputs of tcpdump with the -e flag (which is now
> correct):
>
> root@epsilon:/home/pi/tcpdump/tcpdump-4.9.2# ./tcpdump -X -e -c 1 -n
> -s 100 -i
> wlan0 -l 'ether[10] == 0x18 and ether[2] == 0x0 and ether[3] ==
> 0x0'
> tcpdump: verbose output suppressed, use -v or -vv for full protocol
> decode
> listening on wlan0, link-type IEEE802_11_RADIO (802.11 plus radiotap
> header), ca
> pture size 100
> bytes
> 21:57:51.598450 1.0 Mb/s 2472 MHz 11b -58dBm signal antenna 0
> BSSID:18:d6:c7:51:
> 55:86 DA:ff:ff:ff:ff:ff:ff SA:18:d6:c7:51:55:86 Beacon () [1.0* 2.0 5.5
> 11.0 6.0
> 9.0 12.0 18.0 Mbit] IBSS CH:
> 13[|802.11]
> 0x0000: 8000 0000 ffff ffff ffff 18d6 c751 5586
> .............QU.
> 0x0010: 18d6 c751 5586 c0fa 8061 bb4b 0200 0000
> ...QU....a.K....
> 0x0020: 6400 0000 0000 0108 8204 0b16 0c12 1824 d..............$
> 0x0030: 0301 0d05 0401 0200 0032 0430 4860 6c2d .........2.0H`l-
> 0x0040: 1aee 111b ffff ff00 0000 ..........
> 1 packet captured
> 1 packet received by filter
> 0 packets dropped by kernel
I understand you are saying the above is now correct.
> and without the -e flag (which is probably everythign after the wlan
> header):
>
> root@epsilon:/home/pi/tcpdump/tcpdump-4.9.2# ./tcpdump -X -c 1 -n -s
> 100 -i wl
> an0 -l 'ether[10] == 0x18 and ether[2] == 0x0 and ether[3] ==
> 0x0'
> tcpdump: verbose output suppressed, use -v or -vv for full protocol
> decode
> listening on wlan0, link-type IEEE802_11_RADIO (802.11 plus radiotap
> header), ca
> pture size 100
> bytes
> 21:58:05.627380 1.0 Mb/s 2472 MHz 11b -58dBm signal antenna 0 Beacon ()
> [1.0* 2.
> 0 5.5 11.0 6.0 9.0 12.0 18.0 Mbit] IBSS CH:
> 13[|802.11]
> 0x0000: 8071 914c 0200 0000 6400 0000 0000 0108
> .q.L....d.......
> 0x0010: 8204 0b16 0c12 1824 0301 0d05 0400 0200
> .......$........
> 0x0020: 0032 0430 4860 6c2d 1aee 111b ffff ff00 .2.0H`l-........
> 0x0030: 0000 ..
> 1 packet captured
> 2 packets received by filter
> 0 packets dropped by kernel
I understand the above is now correct as well, right? What is the incorrect
version? Is it incorrect for both "-X -e" and "-e" or just for one of those
cases?
> Lastly as indicated here is my small patch:
>
> --- print-802_11.c.old 2018-04-04 19:40:56.458530097
> +0200
> +++ print-802_11.c 2018-04-04 21:44:15.494773874
> +0200
> @@ -3349,7 +3360,18 @@
> ieee802_11_radio_if_print(netdissect_options
> *ndo,
> const struct pcap_pkthdr *h, const u_char
> *p)
> {
> - return ieee802_11_radio_print(ndo, p, h->len,
> h->caplen);
> + const struct ieee80211_radiotap_header
> *hdr;
> + u_int hdrlen, len;
> +
> + hdr = (const struct ieee80211_radiotap_header
> *)p;
> + len =
> EXTRACT_LE_16BITS(&hdr->it_len);
> +
> + hdrlen = ieee802_11_radio_print(ndo, p, h->len,
> h->caplen);
> + if (ndo->ndo_eflag && hdrlen > len)
> {
> + return len;
> + }
> +
> + return hdrlen;
> }
>
> /*
--
Denis Ovsienko
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