The Tcpdump Group git mirrors - libpcap/blob - pcap-usb-linux-common.c

   1 /*
   2  * Copyright (c) 1993, 1994, 1995, 1996, 1997
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that: (1) source code distributions
   7  * retain the above copyright notice and this paragraph in its entirety, (2)
   8  * distributions including binary code include the above copyright notice and
   9  * this paragraph in its entirety in the documentation or other materials
  10  * provided with the distribution, and (3) all advertising materials mentioning
  11  * features or use of this software display the following acknowledgement:
  12  * ``This product includes software developed by the University of California,
  13  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
  14  * the University nor the names of its contributors may be used to endorse
  15  * or promote products derived from this software without specific prior
  16  * written permission.
  17  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
  18  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
  19  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  20  *
  21  * pcap-usb-linux-common.c - common code for everything that needs to
  22  * deal with Linux USB captures.
  23  */
  24
  25 #include "pcap/pcap.h"
  26 #include "pcap/usb.h"
  27
  28 #include "pcap-usb-linux-common.h"
  29
  30 /*
  31  * Compute, from the data provided by the Linux USB memory-mapped capture
  32  * mechanism, the amount of packet data that would have been provided
  33  * had the capture mechanism not chopped off any data at the end, if, in
  34  * fact, it did so.
  35  *
  36  * Set the "unsliced length" field of the packet header to that value.
  37  */
  38 void
  39 fix_linux_usb_mmapped_length(struct pcap_pkthdr *pkth, const u_char *bp)
  40 {
  41         const pcap_usb_header_mmapped *hdr;
  42         u_int bytes_left;
  43
  44         /*
  45          * All callers of this routine must ensure that pkth->caplen is
  46          * >= sizeof (pcap_usb_header_mmapped).
  47          */
  48         bytes_left = pkth->caplen;
  49         bytes_left -= sizeof (pcap_usb_header_mmapped);
  50
  51         hdr = (const pcap_usb_header_mmapped *) bp;
  52         if (!hdr->data_flag && hdr->transfer_type == URB_ISOCHRONOUS &&
  53             hdr->event_type == URB_COMPLETE &&
  54             (hdr->endpoint_number & URB_TRANSFER_IN) &&
  55             pkth->len == sizeof(pcap_usb_header_mmapped) +
  56                          (hdr->ndesc * sizeof (usb_isodesc)) + hdr->urb_len) {
  57                 usb_isodesc *descs;
  58                 u_int pre_truncation_data_len, pre_truncation_len;
  59
  60                 descs = (usb_isodesc *) (bp + sizeof(pcap_usb_header_mmapped));
  61
  62                 /*
  63                  * We have data (yes, data_flag is 0 if we *do* have data),
  64                  * and this is a "this is complete" incoming isochronous
  65                  * transfer event, and the length was calculated based
  66                  * on the URB length.
  67                  *
  68                  * That's not correct, because the data isn't contiguous,
  69                  * and the isochronous descriptos show how it's scattered.
  70                  *
  71                  * Find the end of the last chunk of data in the buffer
  72                  * referred to by the isochronous descriptors; that indicates
  73                  * how far into the buffer the data would have gone.
  74                  *
  75                  * Make sure we don't run past the end of the captured data
  76                  * while processing the isochronous descriptors.
  77                  */
  78                 pre_truncation_data_len = 0;
  79                 for (uint32_t desc = 0;
  80                     desc < hdr->ndesc && bytes_left >= sizeof (usb_isodesc);
  81                     desc++, bytes_left -= sizeof (usb_isodesc)) {
  82                         u_int desc_end;
  83
  84                         if (descs[desc].len != 0) {
  85                                 desc_end = descs[desc].offset + descs[desc].len;
  86                                 if (desc_end > pre_truncation_data_len)
  87                                         pre_truncation_data_len = desc_end;
  88                         }
  89                 }
  90
  91                 /*
  92                  * Now calculate the total length based on that data
  93                  * length.
  94                  */
  95                 pre_truncation_len = sizeof(pcap_usb_header_mmapped) +
  96                     (hdr->ndesc * sizeof (usb_isodesc)) +
  97                     pre_truncation_data_len;
  98
  99                 /*
 100                  * If that's greater than or equal to the captured length,
 101                  * use that as the length.
 102                  */
 103                 if (pre_truncation_len >= pkth->caplen)
 104                         pkth->len = pre_truncation_len;
 105
 106                 /*
 107                  * If the captured length is greater than the length,
 108                  * use the captured length.
 109                  *
 110                  * For completion events for incoming isochronous transfers,
 111                  * it's based on data_len, which is calculated the same way
 112                  * we calculated pre_truncation_data_len above, except that
 113                  * it has access to all the isochronous descriptors, not
 114                  * just the ones that the kernel were able to provide us or,
 115                  * for a capture file, that weren't sliced off by a snapshot
 116                  * length.
 117                  *
 118                  * However, it might have been reduced by the USB capture
 119                  * mechanism arbitrarily limiting the amount of data it
 120                  * provides to userland, or by the libpcap capture code
 121                  * limiting it to being no more than the snapshot, so
 122                  * we don't want to just use it all the time; we only
 123                  * do so to try to get a better estimate of the actual
 124                  * length - and to make sure the on-the-network length
 125                  * is always >= the captured length.
 126                  */
 127                 if (pkth->caplen > pkth->len)
 128                         pkth->len = pkth->caplen;
 129         }
 130 }