Practicum Status Update Week 8

  • Over the weekend, I’ve talked at the ChaosBBQ in Dortmund, Germany. A nice and small conferency gathering.
  • This week I had only a few bugs (that I reported):
  • The filter stuff is actually more complex than I initially thought: I do indeed have to handle async USB URBs which makes the code look more ugly and taste more like spaghetti. Anyway, the filter stuff should fully work now *yay*.

    I hope the video works. If it doesn’t, please download first. So we can replace packets on the fly, in and out. And of course, you could design a more complex scenario: Let the first read pass by unmodified but after that modify the packets.

  • Read a bit in “Essential Linux Device Drivers” which is an interesting to read book. I like the relaxed writing style. I haven’t gotten to the nitty gritty USB details yet though.
  • Wireshark can sniff USB communication, too. And it can save as a pcap file. And it dissects bits of the protocols. At least it shows the SCSI request for an USB Massstorage. I have to test whether it knows, say, webcams. First investigations show that it only supports USB Massstorage though. And it’d be interesting whether it can sniff the communication I’m filtering with QEmu.
  • Apparently, USB network magic for pcap is 0xdc:
    typedef struct pcap_hdr_s {
            guint32 magic_number;   /* magic number */
            guint16 version_major;  /* major version number */
            guint16 version_minor;  /* minor version number */
            gint32  thiszone;       /* GMT to local correction */
            guint32 sigfigs;        /* accuracy of timestamps */
            guint32 snaplen;        /* max length of captured packets, in octets */
            guint32 network;        /* data link type */
    } pcap_hdr_t;

    Wirehsark dumps the following:

    0000000: d4 c3 b2 a1 02 00 04 00 00 00 00 00 00 00 00 00  ................
    0000010: ff ff 00 00 dc 00 00 00 43 8e 44 4c d7 96 05 00  ........C.DL....

    So I might be able to implement saving to PCap at some stage.

  • Next week will be GUADEC! *yay* But that will also mean that I can’t work that much.
  • So my emulation seems to work now, too. I now need to speak the right protocol. So if you know a good resource that describes how a, say, USB Webcam behaves on the bus, drop me a line. Or anything that can dissect USB packets would be fine.

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