Linux USB: fix incorrect values for the packet length.

Correctly compute the "real" length for isochronous transfers.

When reading memory-mapped Linux capture files, fix up the "real" length
field, in case the file was written by a program doing a capture with
the bug.

1 files changed, 108 insertions, 0 deletions

diff --git a/pcap-usb-linux-common.c b/pcap-usb-linux-common.c
new file mode 100644
index 00000000..ef0bb462
--- /dev/null
+++ b/pcap-usb-linux-common.c
@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 1993, 1994, 1995, 1996, 1997
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that: (1) source code distributions
+ * retain the above copyright notice and this paragraph in its entirety, (2)
+ * distributions including binary code include the above copyright notice and
+ * this paragraph in its entirety in the documentation or other materials
+ * provided with the distribution, and (3) all advertising materials mentioning
+ * features or use of this software display the following acknowledgement:
+ * ``This product includes software developed by the University of California,
+ * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
+ * the University nor the names of its contributors may be used to endorse
+ * or promote products derived from this software without specific prior
+ * written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * pcap-usb-linux-common.c - common code for everything that needs to
+ * deal with Linux USB captures.
+ */
+
+#include "pcap/pcap.h"
+#include "pcap/usb.h"
+
+#include "pcap-usb-linux-common.h"
+
+/*
+ * Compute, from the data provided by the Linux USB memory-mapped capture
+ * mechanism, the amount of packet data that would have been provided
+ * had the capture mechanism not chopped off any data at the end, if, in
+ * fact, it did so.
+ *
+ * Set the "unsliced length" field of the packet header to that value.
+ */
+void
+set_linux_usb_mmapped_length(struct pcap_pkthdr *pkth, const u_char *bp)
+{
+	const pcap_usb_header_mmapped *hdr;
+	u_int bytes_left;
+	
+	bytes_left = pkth->caplen;
+	if (bytes_left < sizeof (pcap_usb_header_mmapped)) {
+		/*
+		 * We don't have the full metadata header, so give up.
+		 */
+		return;
+	}
+	bytes_left -= sizeof (pcap_usb_header_mmapped);
+
+	hdr = (const pcap_usb_header_mmapped *) bp;
+	if (hdr->data_flag) {
+		/*
+		 * No data; just base the on-the-bus length on hdr->data_len
+		 * (so that it's >= the captured length).
+		 */
+		pkth->len = sizeof(pcap_usb_header_mmapped) + hdr->data_len;
+	} else {
+		/*
+		 * We got data; calculate the on-the-bus length based on
+		 * the data length prior to the USB monitor device discarding
+		 * data due to its buffer being too small.
+		 */
+		usb_isodesc *descs;
+		u_int pre_truncation_data_len;
+
+		descs = (usb_isodesc *) (bp + sizeof(pcap_usb_header_mmapped));
+
+		/*
+		 * For most transfers, urb_len is that amount.
+		 */
+		pre_truncation_data_len = hdr->urb_len;
+		if (hdr->transfer_type == URB_ISOCHRONOUS &&
+		    hdr->event_type == URB_COMPLETE &&
+		    (hdr->endpoint_number & URB_TRANSFER_IN)) {
+			/*
+			 * For "this is complete" incoming isochronous
+			 * transfer events, however, the data isn't
+			 * contiguous, and the isochronous descriptos
+			 * show how it's scattered.
+			 *
+			 * Find the end of the last chunk of data in
+			 * the buffer referred to by the isochronous
+			 * descriptors; that indicates how far into
+			 * the buffer the data would have gone.
+			 *
+			 * Make sure we don't run past the end of the
+			 * captured data while processing the isochronous
+			 * descriptors.
+			 */
+			pre_truncation_data_len = 0;
+			for (uint32_t desc = 0;
+			    desc < hdr->ndesc && bytes_left >= sizeof (usb_isodesc);
+			    desc++, bytes_left -= sizeof (usb_isodesc)) {
+				u_int desc_end;
+
+				desc_end = descs[desc].offset + descs[desc].len;
+				if (desc_end > pre_truncation_data_len)
+					pre_truncation_data_len = desc_end;
+			}
+		}
+		pkth->len = sizeof(pcap_usb_header_mmapped) +
+		    (hdr->ndesc * sizeof (usb_isodesc)) +
+		    pre_truncation_data_len;
+	}
+}