1 files changed, 104 insertions, 3 deletions

diff --git a/pcap-usb-linux-common.h b/pcap-usb-linux-common.h
index 8cff7ba1cf6b..333c6b6e0c62 100644
--- a/pcap-usb-linux-common.h
+++ b/pcap-usb-linux-common.h
@@ -19,8 +19,109 @@
  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  *
  * pcap-usb-linux-common.h - common code for everything that needs to
- * deal with Linux USB captures.
+ * deal with Linux USB captures, whether live or in a capture file;
+ * the later means that this is *not* Linux-only.
  */
 
-extern void fix_linux_usb_mmapped_length(struct pcap_pkthdr *pkth,
-    const u_char *bp);
+#include <limits.h>
+
+/*
+ * Return the sum of the two u_int arguments if that sum fits in a u_int,
+ * and return UINT_MAX otherwise.
+ */
+static inline u_int
+u_int_sum(u_int a, u_int b)
+{
+	return (((b) <= UINT_MAX - (a)) ? (a) + (b) : UINT_MAX);
+}
+
+/*
+ * Is this a completion event for an isochronous transfer?
+ */
+static inline int
+is_isochronous_transfer_completion(const pcap_usb_header_mmapped *hdr)
+{
+	return (hdr->transfer_type == URB_ISOCHRONOUS &&
+	    hdr->event_type == URB_COMPLETE &&
+	    (hdr->endpoint_number & URB_TRANSFER_IN));
+}
+
+/*
+ * Total length of the pseudo-header, including the isochronous
+ * descriptors.
+ */
+static inline uint32_t
+iso_pseudo_header_len(const pcap_usb_header_mmapped *usb_hdr)
+{
+	return (sizeof(pcap_usb_header_mmapped) +
+	    usb_hdr->ndesc * sizeof (usb_isodesc));
+}
+
+/*
+ * Calculate the packet length for a "this is complete" incoming
+ * isochronous transfer event.
+ *
+ * Calculating that from hdr->urb_len is not correct, because the
+ * data is not contiguous, and the isochroous descriptors show how
+ * it's scattered.
+ */
+static inline u_int
+incoming_isochronous_transfer_completed_len(struct pcap_pkthdr *phdr,
+    const u_char *bp)
+{
+	const pcap_usb_header_mmapped *hdr;
+	u_int bytes_left;
+	const usb_isodesc *descs;
+	u_int pre_truncation_data_len;
+
+	/*
+	 * All callers of this routine must ensure that pkth->caplen is
+	 * >= sizeof (pcap_usb_header_mmapped).
+	 */
+	bytes_left = phdr->caplen;
+	bytes_left -= sizeof (pcap_usb_header_mmapped);
+
+	hdr = (const pcap_usb_header_mmapped *) bp;
+	descs = (const usb_isodesc *) (bp + sizeof(pcap_usb_header_mmapped));
+
+	/*
+	 * 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;
+
+		if (descs[desc].len != 0) {
+			/*
+			 * Compute the end offset of the data
+			 * for this descriptor, i.e. the offset
+			 * of the byte after the data.  Clamp
+			 * the sum at UINT_MAX, so that it fits
+			 * in a u_int.
+			 */
+			desc_end = u_int_sum(descs[desc].offset,
+			    descs[desc].len);
+			if (desc_end > pre_truncation_data_len)
+				pre_truncation_data_len = desc_end;
+		}
+	}
+
+	/*
+	 * Return the sum of the total header length (memory-mapped
+	 * header and ISO descriptors) and the data length, clamped
+	 * to UINT_MAX.
+	 *
+	 * We've made sure that the number of descriptors is
+	 * <= USB_MAXDESC, so we know that the total size,
+	 * in bytes, of the descriptors fits in a 32-bit
+	 * integer.
+	 */
+	return (u_int_sum(iso_pseudo_header_len(hdr), pre_truncation_data_len));
+}