xref: /freebsd/contrib/libpcap/sf-pcapng.c (revision 2e3f49888ec8851bafb22011533217487764fdb0)

/*
 * 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.
 *
 * sf-pcapng.c - pcapng-file-format-specific code from savefile.c
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <pcap/pcap-inttypes.h>

#include <errno.h>
#include <memory.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "pcap-int.h"
#include "pcap-util.h"

#include "pcap-common.h"

#ifdef HAVE_OS_PROTO_H
#include "os-proto.h"
#endif

#include "sf-pcapng.h"

/*
 * Block types.
 */

/*
 * Common part at the beginning of all blocks.
 */
struct block_header {
	bpf_u_int32	block_type;
	bpf_u_int32	total_length;
};

/*
 * Common trailer at the end of all blocks.
 */
struct block_trailer {
	bpf_u_int32	total_length;
};

/*
 * Common options.
 */
#define OPT_ENDOFOPT	0	/* end of options */
#define OPT_COMMENT	1	/* comment string */

/*
 * Option header.
 */
struct option_header {
	u_short		option_code;
	u_short		option_length;
};

/*
 * Structures for the part of each block type following the common
 * part.
 */

/*
 * Section Header Block.
 */
#define BT_SHB			0x0A0D0D0A
#define BT_SHB_INSANE_MAX       1024U*1024U*1U  /* 1MB should be enough */
struct section_header_block {
	bpf_u_int32	byte_order_magic;
	u_short		major_version;
	u_short		minor_version;
	uint64_t	section_length;
	/* followed by options and trailer */
};

/*
 * Byte-order magic value.
 */
#define BYTE_ORDER_MAGIC	0x1A2B3C4D

/*
 * Current version number.  If major_version isn't PCAP_NG_VERSION_MAJOR,
 * or if minor_version isn't PCAP_NG_VERSION_MINOR or 2, that means that
 * this code can't read the file.
 */
#define PCAP_NG_VERSION_MAJOR	1
#define PCAP_NG_VERSION_MINOR	0

/*
 * Interface Description Block.
 */
#define BT_IDB			0x00000001

struct interface_description_block {
	u_short		linktype;
	u_short		reserved;
	bpf_u_int32	snaplen;
	/* followed by options and trailer */
};

/*
 * Options in the IDB.
 */
#define IF_NAME		2	/* interface name string */
#define IF_DESCRIPTION	3	/* interface description string */
#define IF_IPV4ADDR	4	/* interface's IPv4 address and netmask */
#define IF_IPV6ADDR	5	/* interface's IPv6 address and prefix length */
#define IF_MACADDR	6	/* interface's MAC address */
#define IF_EUIADDR	7	/* interface's EUI address */
#define IF_SPEED	8	/* interface's speed, in bits/s */
#define IF_TSRESOL	9	/* interface's time stamp resolution */
#define IF_TZONE	10	/* interface's time zone */
#define IF_FILTER	11	/* filter used when capturing on interface */
#define IF_OS		12	/* string OS on which capture on this interface was done */
#define IF_FCSLEN	13	/* FCS length for this interface */
#define IF_TSOFFSET	14	/* time stamp offset for this interface */

/*
 * Enhanced Packet Block.
 */
#define BT_EPB			0x00000006

struct enhanced_packet_block {
	bpf_u_int32	interface_id;
	bpf_u_int32	timestamp_high;
	bpf_u_int32	timestamp_low;
	bpf_u_int32	caplen;
	bpf_u_int32	len;
	/* followed by packet data, options, and trailer */
};

/*
 * Simple Packet Block.
 */
#define BT_SPB			0x00000003

struct simple_packet_block {
	bpf_u_int32	len;
	/* followed by packet data and trailer */
};

/*
 * Packet Block.
 */
#define BT_PB			0x00000002

struct packet_block {
	u_short		interface_id;
	u_short		drops_count;
	bpf_u_int32	timestamp_high;
	bpf_u_int32	timestamp_low;
	bpf_u_int32	caplen;
	bpf_u_int32	len;
	/* followed by packet data, options, and trailer */
};

/*
 * Block cursor - used when processing the contents of a block.
 * Contains a pointer into the data being processed and a count
 * of bytes remaining in the block.
 */
struct block_cursor {
	u_char		*data;
	size_t		data_remaining;
	bpf_u_int32	block_type;
};

typedef enum {
	PASS_THROUGH,
	SCALE_UP_DEC,
	SCALE_DOWN_DEC,
	SCALE_UP_BIN,
	SCALE_DOWN_BIN
} tstamp_scale_type_t;

/*
 * Per-interface information.
 */
struct pcap_ng_if {
	uint32_t snaplen;		/* snapshot length */
	uint64_t tsresol;		/* time stamp resolution */
	tstamp_scale_type_t scale_type;	/* how to scale */
	uint64_t scale_factor;		/* time stamp scale factor for power-of-10 tsresol */
	uint64_t tsoffset;		/* time stamp offset */
};

/*
 * Per-pcap_t private data.
 *
 * max_blocksize is the maximum size of a block that we'll accept.  We
 * reject blocks bigger than this, so we don't consume too much memory
 * with a truly huge block.  It can change as we see IDBs with different
 * link-layer header types.  (Currently, we don't support IDBs with
 * different link-layer header types, but we will support it in the
 * future, when we offer file-reading APIs that support it.)
 *
 * XXX - that's an issue on ILP32 platforms, where the maximum block
 * size of 2^31-1 would eat all but one byte of the entire address space.
 * It's less of an issue on ILP64/LLP64 platforms, but the actual size
 * of the address space may be limited by 1) the number of *significant*
 * address bits (currently, x86-64 only supports 48 bits of address), 2)
 * any limitations imposed by the operating system; 3) any limitations
 * imposed by the amount of available backing store for anonymous pages,
 * so we impose a limit regardless of the size of a pointer.
 */
struct pcap_ng_sf {
	uint64_t user_tsresol;		/* time stamp resolution requested by the user */
	u_int max_blocksize;		/* don't grow buffer size past this */
	bpf_u_int32 ifcount;		/* number of interfaces seen in this capture */
	bpf_u_int32 ifaces_size;	/* size of array below */
	struct pcap_ng_if *ifaces;	/* array of interface information */
};

/*
 * The maximum block size we start with; we use an arbitrary value of
 * 16 MiB.
 */
#define INITIAL_MAX_BLOCKSIZE	(16*1024*1024)

/*
 * Maximum block size for a given maximum snapshot length; we define it
 * as the size of an EPB with a max_snaplen-sized packet and 128KB of
 * options.
 */
#define MAX_BLOCKSIZE_FOR_SNAPLEN(max_snaplen) \
	(sizeof (struct block_header) + \
	 sizeof (struct enhanced_packet_block) + \
	 (max_snaplen) + 131072 + \
	 sizeof (struct block_trailer))

static void pcap_ng_cleanup(pcap_t *p);
static int pcap_ng_next_packet(pcap_t *p, struct pcap_pkthdr *hdr,
    u_char **data);

static int
read_bytes(FILE *fp, void *buf, size_t bytes_to_read, int fail_on_eof,
    char *errbuf)
{
	size_t amt_read;

	amt_read = fread(buf, 1, bytes_to_read, fp);
	if (amt_read != bytes_to_read) {
		if (ferror(fp)) {
			pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
			    errno, "error reading dump file");
		} else {
			if (amt_read == 0 && !fail_on_eof)
				return (0);	/* EOF */
			snprintf(errbuf, PCAP_ERRBUF_SIZE,
			    "truncated pcapng dump file; tried to read %zu bytes, only got %zu",
			    bytes_to_read, amt_read);
		}
		return (-1);
	}
	return (1);
}

static int
read_block(FILE *fp, pcap_t *p, struct block_cursor *cursor, char *errbuf)
{
	struct pcap_ng_sf *ps;
	int status;
	struct block_header bhdr;
	struct block_trailer *btrlr;
	u_char *bdata;
	size_t data_remaining;

	ps = p->priv;

	status = read_bytes(fp, &bhdr, sizeof(bhdr), 0, errbuf);
	if (status <= 0)
		return (status);	/* error or EOF */

	if (p->swapped) {
		bhdr.block_type = SWAPLONG(bhdr.block_type);
		bhdr.total_length = SWAPLONG(bhdr.total_length);
	}

	/*
	 * Is this block "too small" - i.e., is it shorter than a block
	 * header plus a block trailer?
	 */
	if (bhdr.total_length < sizeof(struct block_header) +
	    sizeof(struct block_trailer)) {
		snprintf(errbuf, PCAP_ERRBUF_SIZE,
		    "block in pcapng dump file has a length of %u < %zu",
		    bhdr.total_length,
		    sizeof(struct block_header) + sizeof(struct block_trailer));
		return (-1);
	}

	/*
	 * Is the block total length a multiple of 4?
	 */
	if ((bhdr.total_length % 4) != 0) {
		/*
		 * No.  Report that as an error.
		 */
		snprintf(errbuf, PCAP_ERRBUF_SIZE,
		    "block in pcapng dump file has a length of %u that is not a multiple of 4",
		    bhdr.total_length);
		return (-1);
	}

	/*
	 * Is the buffer big enough?
	 */
	if (p->bufsize < bhdr.total_length) {
		/*
		 * No - make it big enough, unless it's too big, in
		 * which case we fail.
		 */
		void *bigger_buffer;

		if (bhdr.total_length > ps->max_blocksize) {
			snprintf(errbuf, PCAP_ERRBUF_SIZE, "pcapng block size %u > maximum %u", bhdr.total_length,
			    ps->max_blocksize);
			return (-1);
		}
		bigger_buffer = realloc(p->buffer, bhdr.total_length);
		if (bigger_buffer == NULL) {
			snprintf(errbuf, PCAP_ERRBUF_SIZE, "out of memory");
			return (-1);
		}
		p->buffer = bigger_buffer;
	}

	/*
	 * Copy the stuff we've read to the buffer, and read the rest
	 * of the block.
	 */
	memcpy(p->buffer, &bhdr, sizeof(bhdr));
	bdata = (u_char *)p->buffer + sizeof(bhdr);
	data_remaining = bhdr.total_length - sizeof(bhdr);
	if (read_bytes(fp, bdata, data_remaining, 1, errbuf) == -1)
		return (-1);

	/*
	 * Get the block size from the trailer.
	 */
	btrlr = (struct block_trailer *)(bdata + data_remaining - sizeof (struct block_trailer));
	if (p->swapped)
		btrlr->total_length = SWAPLONG(btrlr->total_length);

	/*
	 * Is the total length from the trailer the same as the total
	 * length from the header?
	 */
	if (bhdr.total_length != btrlr->total_length) {
		/*
		 * No.
		 */
		snprintf(errbuf, PCAP_ERRBUF_SIZE,
		    "block total length in header and trailer don't match");
		return (-1);
	}

	/*
	 * Initialize the cursor.
	 */
	cursor->data = bdata;
	cursor->data_remaining = data_remaining - sizeof(struct block_trailer);
	cursor->block_type = bhdr.block_type;
	return (1);
}

static void *
get_from_block_data(struct block_cursor *cursor, size_t chunk_size,
    char *errbuf)
{
	void *data;

	/*
	 * Make sure we have the specified amount of data remaining in
	 * the block data.
	 */
	if (cursor->data_remaining < chunk_size) {
		snprintf(errbuf, PCAP_ERRBUF_SIZE,
		    "block of type %u in pcapng dump file is too short",
		    cursor->block_type);
		return (NULL);
	}

	/*
	 * Return the current pointer, and skip past the chunk.
	 */
	data = cursor->data;
	cursor->data += chunk_size;
	cursor->data_remaining -= chunk_size;
	return (data);
}

static struct option_header *
get_opthdr_from_block_data(pcap_t *p, struct block_cursor *cursor, char *errbuf)
{
	struct option_header *opthdr;

	opthdr = get_from_block_data(cursor, sizeof(*opthdr), errbuf);
	if (opthdr == NULL) {
		/*
		 * Option header is cut short.
		 */
		return (NULL);
	}

	/*
	 * Byte-swap it if necessary.
	 */
	if (p->swapped) {
		opthdr->option_code = SWAPSHORT(opthdr->option_code);
		opthdr->option_length = SWAPSHORT(opthdr->option_length);
	}

	return (opthdr);
}

static void *
get_optvalue_from_block_data(struct block_cursor *cursor,
    struct option_header *opthdr, char *errbuf)
{
	size_t padded_option_len;
	void *optvalue;

	/* Pad option length to 4-byte boundary */
	padded_option_len = opthdr->option_length;
	padded_option_len = ((padded_option_len + 3)/4)*4;

	optvalue = get_from_block_data(cursor, padded_option_len, errbuf);
	if (optvalue == NULL) {
		/*
		 * Option value is cut short.
		 */
		return (NULL);
	}

	return (optvalue);
}

static int
process_idb_options(pcap_t *p, struct block_cursor *cursor, uint64_t *tsresol,
    uint64_t *tsoffset, int *is_binary, char *errbuf)
{
	struct option_header *opthdr;
	void *optvalue;
	int saw_tsresol, saw_tsoffset;
	uint8_t tsresol_opt;
	u_int i;

	saw_tsresol = 0;
	saw_tsoffset = 0;
	while (cursor->data_remaining != 0) {
		/*
		 * Get the option header.
		 */
		opthdr = get_opthdr_from_block_data(p, cursor, errbuf);
		if (opthdr == NULL) {
			/*
			 * Option header is cut short.
			 */
			return (-1);
		}

		/*
		 * Get option value.
		 */
		optvalue = get_optvalue_from_block_data(cursor, opthdr,
		    errbuf);
		if (optvalue == NULL) {
			/*
			 * Option value is cut short.
			 */
			return (-1);
		}

		switch (opthdr->option_code) {

		case OPT_ENDOFOPT:
			if (opthdr->option_length != 0) {
				snprintf(errbuf, PCAP_ERRBUF_SIZE,
				    "Interface Description Block has opt_endofopt option with length %u != 0",
				    opthdr->option_length);
				return (-1);
			}
			goto done;

		case IF_TSRESOL:
			if (opthdr->option_length != 1) {
				snprintf(errbuf, PCAP_ERRBUF_SIZE,
				    "Interface Description Block has if_tsresol option with length %u != 1",
				    opthdr->option_length);
				return (-1);
			}
			if (saw_tsresol) {
				snprintf(errbuf, PCAP_ERRBUF_SIZE,
				    "Interface Description Block has more than one if_tsresol option");
				return (-1);
			}
			saw_tsresol = 1;
			memcpy(&tsresol_opt, optvalue, sizeof(tsresol_opt));
			if (tsresol_opt & 0x80) {
				/*
				 * Resolution is negative power of 2.
				 */
				uint8_t tsresol_shift = (tsresol_opt & 0x7F);

				if (tsresol_shift > 63) {
					/*
					 * Resolution is too high; 2^-{res}
					 * won't fit in a 64-bit value.
					 */
					snprintf(errbuf, PCAP_ERRBUF_SIZE,
					    "Interface Description Block if_tsresol option resolution 2^-%u is too high",
					    tsresol_shift);
					return (-1);
				}
				*is_binary = 1;
				*tsresol = ((uint64_t)1) << tsresol_shift;
			} else {
				/*
				 * Resolution is negative power of 10.
				 */
				if (tsresol_opt > 19) {
					/*
					 * Resolution is too high; 2^-{res}
					 * won't fit in a 64-bit value (the
					 * largest power of 10 that fits
					 * in a 64-bit value is 10^19, as
					 * the largest 64-bit unsigned
					 * value is ~1.8*10^19).
					 */
					snprintf(errbuf, PCAP_ERRBUF_SIZE,
					    "Interface Description Block if_tsresol option resolution 10^-%u is too high",
					    tsresol_opt);
					return (-1);
				}
				*is_binary = 0;
				*tsresol = 1;
				for (i = 0; i < tsresol_opt; i++)
					*tsresol *= 10;
			}
			break;

		case IF_TSOFFSET:
			if (opthdr->option_length != 8) {
				snprintf(errbuf, PCAP_ERRBUF_SIZE,
				    "Interface Description Block has if_tsoffset option with length %u != 8",
				    opthdr->option_length);
				return (-1);
			}
			if (saw_tsoffset) {
				snprintf(errbuf, PCAP_ERRBUF_SIZE,
				    "Interface Description Block has more than one if_tsoffset option");
				return (-1);
			}
			saw_tsoffset = 1;
			memcpy(tsoffset, optvalue, sizeof(*tsoffset));
			if (p->swapped)
				*tsoffset = SWAPLL(*tsoffset);
			break;

		default:
			break;
		}
	}

done:
	return (0);
}

static int
add_interface(pcap_t *p, struct interface_description_block *idbp,
    struct block_cursor *cursor, char *errbuf)
{
	struct pcap_ng_sf *ps;
	uint64_t tsresol;
	uint64_t tsoffset;
	int is_binary;

	ps = p->priv;

	/*
	 * Count this interface.
	 */
	ps->ifcount++;

	/*
	 * Grow the array of per-interface information as necessary.
	 */
	if (ps->ifcount > ps->ifaces_size) {
		/*
		 * We need to grow the array.
		 */
		bpf_u_int32 new_ifaces_size;
		struct pcap_ng_if *new_ifaces;

		if (ps->ifaces_size == 0) {
			/*
			 * It's currently empty.
			 *
			 * (The Clang static analyzer doesn't do enough,
			 * err, umm, dataflow *analysis* to realize that
			 * ps->ifaces_size == 0 if ps->ifaces == NULL,
			 * and so complains about a possible zero argument
			 * to realloc(), so we check for the former
			 * condition to shut it up.
			 *
			 * However, it doesn't complain that one of the
			 * multiplications below could overflow, which is
			 * a real, albeit extremely unlikely, problem (you'd
			 * need a pcapng file with tens of millions of
			 * interfaces).)
			 */
			new_ifaces_size = 1;
			new_ifaces = malloc(sizeof (struct pcap_ng_if));
		} else {
			/*
			 * It's not currently empty; double its size.
			 * (Perhaps overkill once we have a lot of interfaces.)
			 *
			 * Check for overflow if we double it.
			 */
			if (ps->ifaces_size * 2 < ps->ifaces_size) {
				/*
				 * The maximum number of interfaces before
				 * ps->ifaces_size overflows is the largest
				 * possible 32-bit power of 2, as we do
				 * size doubling.
				 */
				snprintf(errbuf, PCAP_ERRBUF_SIZE,
				    "more than %u interfaces in the file",
				    0x80000000U);
				return (0);
			}

			/*
			 * ps->ifaces_size * 2 doesn't overflow, so it's
			 * safe to multiply.
			 */
			new_ifaces_size = ps->ifaces_size * 2;

			/*
			 * Now make sure that's not so big that it overflows
			 * if we multiply by sizeof (struct pcap_ng_if).
			 *
			 * That can happen on 32-bit platforms, with a 32-bit
			 * size_t; it shouldn't happen on 64-bit platforms,
			 * with a 64-bit size_t, as new_ifaces_size is
			 * 32 bits.
			 */
			if (new_ifaces_size * sizeof (struct pcap_ng_if) < new_ifaces_size) {
				/*
				 * As this fails only with 32-bit size_t,
				 * the multiplication was 32x32->32, and
				 * the largest 32-bit value that can safely
				 * be multiplied by sizeof (struct pcap_ng_if)
				 * without overflow is the largest 32-bit
				 * (unsigned) value divided by
				 * sizeof (struct pcap_ng_if).
				 */
				snprintf(errbuf, PCAP_ERRBUF_SIZE,
				    "more than %u interfaces in the file",
				    0xFFFFFFFFU / ((u_int)sizeof (struct pcap_ng_if)));
				return (0);
			}
			new_ifaces = realloc(ps->ifaces, new_ifaces_size * sizeof (struct pcap_ng_if));
		}
		if (new_ifaces == NULL) {
			/*
			 * We ran out of memory.
			 * Give up.
			 */
			snprintf(errbuf, PCAP_ERRBUF_SIZE,
			    "out of memory for per-interface information (%u interfaces)",
			    ps->ifcount);
			return (0);
		}
		ps->ifaces_size = new_ifaces_size;
		ps->ifaces = new_ifaces;
	}

	ps->ifaces[ps->ifcount - 1].snaplen = idbp->snaplen;

	/*
	 * Set the default time stamp resolution and offset.
	 */
	tsresol = 1000000;	/* microsecond resolution */
	is_binary = 0;		/* which is a power of 10 */
	tsoffset = 0;		/* absolute timestamps */

	/*
	 * Now look for various time stamp options, so we know
	 * how to interpret the time stamps for this interface.
	 */
	if (process_idb_options(p, cursor, &tsresol, &tsoffset, &is_binary,
	    errbuf) == -1)
		return (0);

	ps->ifaces[ps->ifcount - 1].tsresol = tsresol;
	ps->ifaces[ps->ifcount - 1].tsoffset = tsoffset;

	/*
	 * Determine whether we're scaling up or down or not
	 * at all for this interface.
	 */
	if (tsresol == ps->user_tsresol) {
		/*
		 * The resolution is the resolution the user wants,
		 * so we don't have to do scaling.
		 */
		ps->ifaces[ps->ifcount - 1].scale_type = PASS_THROUGH;
	} else if (tsresol > ps->user_tsresol) {
		/*
		 * The resolution is greater than what the user wants,
		 * so we have to scale the timestamps down.
		 */
		if (is_binary)
			ps->ifaces[ps->ifcount - 1].scale_type = SCALE_DOWN_BIN;
		else {
			/*
			 * Calculate the scale factor.
			 */
			ps->ifaces[ps->ifcount - 1].scale_factor = tsresol/ps->user_tsresol;
			ps->ifaces[ps->ifcount - 1].scale_type = SCALE_DOWN_DEC;
		}
	} else {
		/*
		 * The resolution is less than what the user wants,
		 * so we have to scale the timestamps up.
		 */
		if (is_binary)
			ps->ifaces[ps->ifcount - 1].scale_type = SCALE_UP_BIN;
		else {
			/*
			 * Calculate the scale factor.
			 */
			ps->ifaces[ps->ifcount - 1].scale_factor = ps->user_tsresol/tsresol;
			ps->ifaces[ps->ifcount - 1].scale_type = SCALE_UP_DEC;
		}
	}
	return (1);
}

/*
 * Check whether this is a pcapng savefile and, if it is, extract the
 * relevant information from the header.
 */
pcap_t *
pcap_ng_check_header(const uint8_t *magic, FILE *fp, u_int precision,
    char *errbuf, int *err)
{
	bpf_u_int32 magic_int;
	size_t amt_read;
	bpf_u_int32 total_length;
	bpf_u_int32 byte_order_magic;
	struct block_header *bhdrp;
	struct section_header_block *shbp;
	pcap_t *p;
	int swapped = 0;
	struct pcap_ng_sf *ps;
	int status;
	struct block_cursor cursor;
	struct interface_description_block *idbp;

	/*
	 * Assume no read errors.
	 */
	*err = 0;

	/*
	 * Check whether the first 4 bytes of the file are the block
	 * type for a pcapng savefile.
	 */
	memcpy(&magic_int, magic, sizeof(magic_int));
	if (magic_int != BT_SHB) {
		/*
		 * XXX - check whether this looks like what the block
		 * type would be after being munged by mapping between
		 * UN*X and DOS/Windows text file format and, if it
		 * does, look for the byte-order magic number in
		 * the appropriate place and, if we find it, report
		 * this as possibly being a pcapng file transferred
		 * between UN*X and Windows in text file format?
		 */
		return (NULL);	/* nope */
	}

	/*
	 * OK, they are.  However, that's just \n\r\r\n, so it could,
	 * conceivably, be an ordinary text file.
	 *
	 * It could not, however, conceivably be any other type of
	 * capture file, so we can read the rest of the putative
	 * Section Header Block; put the block type in the common
	 * header, read the rest of the common header and the
	 * fixed-length portion of the SHB, and look for the byte-order
	 * magic value.
	 */
	amt_read = fread(&total_length, 1, sizeof(total_length), fp);
	if (amt_read < sizeof(total_length)) {
		if (ferror(fp)) {
			pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
			    errno, "error reading dump file");
			*err = 1;
			return (NULL);	/* fail */
		}

		/*
		 * Possibly a weird short text file, so just say
		 * "not pcapng".
		 */
		return (NULL);
	}
	amt_read = fread(&byte_order_magic, 1, sizeof(byte_order_magic), fp);
	if (amt_read < sizeof(byte_order_magic)) {
		if (ferror(fp)) {
			pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
			    errno, "error reading dump file");
			*err = 1;
			return (NULL);	/* fail */
		}

		/*
		 * Possibly a weird short text file, so just say
		 * "not pcapng".
		 */
		return (NULL);
	}
	if (byte_order_magic != BYTE_ORDER_MAGIC) {
		byte_order_magic = SWAPLONG(byte_order_magic);
		if (byte_order_magic != BYTE_ORDER_MAGIC) {
			/*
			 * Not a pcapng file.
			 */
			return (NULL);
		}
		swapped = 1;
		total_length = SWAPLONG(total_length);
	}

	/*
	 * Check the sanity of the total length.
	 */
	if (total_length < sizeof(*bhdrp) + sizeof(*shbp) + sizeof(struct block_trailer) ||
            (total_length > BT_SHB_INSANE_MAX)) {
		snprintf(errbuf, PCAP_ERRBUF_SIZE,
		    "Section Header Block in pcapng dump file has invalid length %zu < _%u_ < %u (BT_SHB_INSANE_MAX)",
		    sizeof(*bhdrp) + sizeof(*shbp) + sizeof(struct block_trailer),
		    total_length,
		    BT_SHB_INSANE_MAX);

		*err = 1;
		return (NULL);
	}

	/*
	 * OK, this is a good pcapng file.
	 * Allocate a pcap_t for it.
	 */
	p = PCAP_OPEN_OFFLINE_COMMON(errbuf, struct pcap_ng_sf);
	if (p == NULL) {
		/* Allocation failed. */
		*err = 1;
		return (NULL);
	}
	p->swapped = swapped;
	ps = p->priv;

	/*
	 * What precision does the user want?
	 */
	switch (precision) {

	case PCAP_TSTAMP_PRECISION_MICRO:
		ps->user_tsresol = 1000000;
		break;

	case PCAP_TSTAMP_PRECISION_NANO:
		ps->user_tsresol = 1000000000;
		break;

	default:
		snprintf(errbuf, PCAP_ERRBUF_SIZE,
		    "unknown time stamp resolution %u", precision);
		free(p);
		*err = 1;
		return (NULL);
	}

	p->opt.tstamp_precision = precision;

	/*
	 * Allocate a buffer into which to read blocks.  We default to
	 * the maximum of:
	 *
	 *	the total length of the SHB for which we read the header;
	 *
	 *	2K, which should be more than large enough for an Enhanced
	 *	Packet Block containing a full-size Ethernet frame, and
	 *	leaving room for some options.
	 *
	 * If we find a bigger block, we reallocate the buffer, up to
	 * the maximum size.  We start out with a maximum size of
	 * INITIAL_MAX_BLOCKSIZE; if we see any link-layer header types
	 * with a maximum snapshot that results in a larger maximum
	 * block length, we boost the maximum.
	 */
	p->bufsize = 2048;
	if (p->bufsize < total_length)
		p->bufsize = total_length;
	p->buffer = malloc(p->bufsize);
	if (p->buffer == NULL) {
		snprintf(errbuf, PCAP_ERRBUF_SIZE, "out of memory");
		free(p);
		*err = 1;
		return (NULL);
	}
	ps->max_blocksize = INITIAL_MAX_BLOCKSIZE;

	/*
	 * Copy the stuff we've read to the buffer, and read the rest
	 * of the SHB.
	 */
	bhdrp = (struct block_header *)p->buffer;
	shbp = (struct section_header_block *)((u_char *)p->buffer + sizeof(struct block_header));
	bhdrp->block_type = magic_int;
	bhdrp->total_length = total_length;
	shbp->byte_order_magic = byte_order_magic;
	if (read_bytes(fp,
	    (u_char *)p->buffer + (sizeof(magic_int) + sizeof(total_length) + sizeof(byte_order_magic)),
	    total_length - (sizeof(magic_int) + sizeof(total_length) + sizeof(byte_order_magic)),
	    1, errbuf) == -1)
		goto fail;

	if (p->swapped) {
		/*
		 * Byte-swap the fields we've read.
		 */
		shbp->major_version = SWAPSHORT(shbp->major_version);
		shbp->minor_version = SWAPSHORT(shbp->minor_version);

		/*
		 * XXX - we don't care about the section length.
		 */
	}
	/* Currently only SHB versions 1.0 and 1.2 are supported;
	   version 1.2 is treated as being the same as version 1.0.
	   See the current version of the pcapng specification.

	   Version 1.2 is written by some programs that write additional
	   block types (which can be read by any code that handles them,
	   regardless of whether the minor version if 0 or 2, so that's
	   not a reason to change the minor version number).

	   XXX - the pcapng specification says that readers should
	   just ignore sections with an unsupported version number;
	   presumably they can also report an error if they skip
	   all the way to the end of the file without finding
	   any versions that they support. */
	if (! (shbp->major_version == PCAP_NG_VERSION_MAJOR &&
	       (shbp->minor_version == PCAP_NG_VERSION_MINOR ||
	        shbp->minor_version == 2))) {
		snprintf(errbuf, PCAP_ERRBUF_SIZE,
		    "unsupported pcapng savefile version %u.%u",
		    shbp->major_version, shbp->minor_version);
		goto fail;
	}
	p->version_major = shbp->major_version;
	p->version_minor = shbp->minor_version;

	/*
	 * Save the time stamp resolution the user requested.
	 */
	p->opt.tstamp_precision = precision;

	/*
	 * Now start looking for an Interface Description Block.
	 */
	for (;;) {
		/*
		 * Read the next block.
		 */
		status = read_block(fp, p, &cursor, errbuf);
		if (status == 0) {
			/* EOF - no IDB in this file */
			snprintf(errbuf, PCAP_ERRBUF_SIZE,
			    "the capture file has no Interface Description Blocks");
			goto fail;
		}
		if (status == -1)
			goto fail;	/* error */
		switch (cursor.block_type) {

		case BT_IDB:
			/*
			 * Get a pointer to the fixed-length portion of the
			 * IDB.
			 */
			idbp = get_from_block_data(&cursor, sizeof(*idbp),
			    errbuf);
			if (idbp == NULL)
				goto fail;	/* error */

			/*
			 * Byte-swap it if necessary.
			 */
			if (p->swapped) {
				idbp->linktype = SWAPSHORT(idbp->linktype);
				idbp->snaplen = SWAPLONG(idbp->snaplen);
			}

			/*
			 * Try to add this interface.
			 */
			if (!add_interface(p, idbp, &cursor, errbuf))
				goto fail;

			goto done;

		case BT_EPB:
		case BT_SPB:
		case BT_PB:
			/*
			 * Saw a packet before we saw any IDBs.  That's
			 * not valid, as we don't know what link-layer
			 * encapsulation the packet has.
			 */
			snprintf(errbuf, PCAP_ERRBUF_SIZE,
			    "the capture file has a packet block before any Interface Description Blocks");
			goto fail;

		default:
			/*
			 * Just ignore it.
			 */
			break;
		}
	}

done:
	p->linktype = linktype_to_dlt(idbp->linktype);
	p->snapshot = pcap_adjust_snapshot(p->linktype, idbp->snaplen);
	p->linktype_ext = 0;

	/*
	 * If the maximum block size for a packet with the maximum
	 * snapshot length for this DLT_ is bigger than the current
	 * maximum block size, increase the maximum.
	 */
	if (MAX_BLOCKSIZE_FOR_SNAPLEN(max_snaplen_for_dlt(p->linktype)) > ps->max_blocksize)
		ps->max_blocksize = MAX_BLOCKSIZE_FOR_SNAPLEN(max_snaplen_for_dlt(p->linktype));

	p->next_packet_op = pcap_ng_next_packet;
	p->cleanup_op = pcap_ng_cleanup;

	return (p);

fail:
	free(ps->ifaces);
	free(p->buffer);
	free(p);
	*err = 1;
	return (NULL);
}

static void
pcap_ng_cleanup(pcap_t *p)
{
	struct pcap_ng_sf *ps = p->priv;

	free(ps->ifaces);
	sf_cleanup(p);
}

/*
 * Read and return the next packet from the savefile.  Return the header
 * in hdr and a pointer to the contents in data.  Return 1 on success, 0
 * if there were no more packets, and -1 on an error.
 */
static int
pcap_ng_next_packet(pcap_t *p, struct pcap_pkthdr *hdr, u_char **data)
{
	struct pcap_ng_sf *ps = p->priv;
	struct block_cursor cursor;
	int status;
	struct enhanced_packet_block *epbp;
	struct simple_packet_block *spbp;
	struct packet_block *pbp;
	bpf_u_int32 interface_id = 0xFFFFFFFF;
	struct interface_description_block *idbp;
	struct section_header_block *shbp;
	FILE *fp = p->rfile;
	uint64_t t, sec, frac;

	/*
	 * Look for an Enhanced Packet Block, a Simple Packet Block,
	 * or a Packet Block.
	 */
	for (;;) {
		/*
		 * Read the block type and length; those are common
		 * to all blocks.
		 */
		status = read_block(fp, p, &cursor, p->errbuf);
		if (status == 0)
			return (0);	/* EOF */
		if (status == -1)
			return (-1);	/* error */
		switch (cursor.block_type) {

		case BT_EPB:
			/*
			 * Get a pointer to the fixed-length portion of the
			 * EPB.
			 */
			epbp = get_from_block_data(&cursor, sizeof(*epbp),
			    p->errbuf);
			if (epbp == NULL)
				return (-1);	/* error */

			/*
			 * Byte-swap it if necessary.
			 */
			if (p->swapped) {
				/* these were written in opposite byte order */
				interface_id = SWAPLONG(epbp->interface_id);
				hdr->caplen = SWAPLONG(epbp->caplen);
				hdr->len = SWAPLONG(epbp->len);
				t = ((uint64_t)SWAPLONG(epbp->timestamp_high)) << 32 |
				    SWAPLONG(epbp->timestamp_low);
			} else {
				interface_id = epbp->interface_id;
				hdr->caplen = epbp->caplen;
				hdr->len = epbp->len;
				t = ((uint64_t)epbp->timestamp_high) << 32 |
				    epbp->timestamp_low;
			}
			goto found;

		case BT_SPB:
			/*
			 * Get a pointer to the fixed-length portion of the
			 * SPB.
			 */
			spbp = get_from_block_data(&cursor, sizeof(*spbp),
			    p->errbuf);
			if (spbp == NULL)
				return (-1);	/* error */

			/*
			 * SPB packets are assumed to have arrived on
			 * the first interface.
			 */
			interface_id = 0;

			/*
			 * Byte-swap it if necessary.
			 */
			if (p->swapped) {
				/* these were written in opposite byte order */
				hdr->len = SWAPLONG(spbp->len);
			} else
				hdr->len = spbp->len;

			/*
			 * The SPB doesn't give the captured length;
			 * it's the minimum of the snapshot length
			 * and the packet length.
			 */
			hdr->caplen = hdr->len;
			if (hdr->caplen > (bpf_u_int32)p->snapshot)
				hdr->caplen = p->snapshot;
			t = 0;	/* no time stamps */
			goto found;

		case BT_PB:
			/*
			 * Get a pointer to the fixed-length portion of the
			 * PB.
			 */
			pbp = get_from_block_data(&cursor, sizeof(*pbp),
			    p->errbuf);
			if (pbp == NULL)
				return (-1);	/* error */

			/*
			 * Byte-swap it if necessary.
			 */
			if (p->swapped) {
				/* these were written in opposite byte order */
				interface_id = SWAPSHORT(pbp->interface_id);
				hdr->caplen = SWAPLONG(pbp->caplen);
				hdr->len = SWAPLONG(pbp->len);
				t = ((uint64_t)SWAPLONG(pbp->timestamp_high)) << 32 |
				    SWAPLONG(pbp->timestamp_low);
			} else {
				interface_id = pbp->interface_id;
				hdr->caplen = pbp->caplen;
				hdr->len = pbp->len;
				t = ((uint64_t)pbp->timestamp_high) << 32 |
				    pbp->timestamp_low;
			}
			goto found;

		case BT_IDB:
			/*
			 * Interface Description Block.  Get a pointer
			 * to its fixed-length portion.
			 */
			idbp = get_from_block_data(&cursor, sizeof(*idbp),
			    p->errbuf);
			if (idbp == NULL)
				return (-1);	/* error */

			/*
			 * Byte-swap it if necessary.
			 */
			if (p->swapped) {
				idbp->linktype = SWAPSHORT(idbp->linktype);
				idbp->snaplen = SWAPLONG(idbp->snaplen);
			}

			/*
			 * If the link-layer type or snapshot length
			 * differ from the ones for the first IDB we
			 * saw, quit.
			 *
			 * XXX - just discard packets from those
			 * interfaces?
			 */
			if (p->linktype != idbp->linktype) {
				snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
				    "an interface has a type %u different from the type of the first interface",
				    idbp->linktype);
				return (-1);
			}

			/*
			 * Check against the *adjusted* value of this IDB's
			 * snapshot length.
			 */
			if ((bpf_u_int32)p->snapshot !=
			    pcap_adjust_snapshot(p->linktype, idbp->snaplen)) {
				snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
				    "an interface has a snapshot length %u different from the snapshot length of the first interface",
				    idbp->snaplen);
				return (-1);
			}

			/*
			 * Try to add this interface.
			 */
			if (!add_interface(p, idbp, &cursor, p->errbuf))
				return (-1);
			break;

		case BT_SHB:
			/*
			 * Section Header Block.  Get a pointer
			 * to its fixed-length portion.
			 */
			shbp = get_from_block_data(&cursor, sizeof(*shbp),
			    p->errbuf);
			if (shbp == NULL)
				return (-1);	/* error */

			/*
			 * Assume the byte order of this section is
			 * the same as that of the previous section.
			 * We'll check for that later.
			 */
			if (p->swapped) {
				shbp->byte_order_magic =
				    SWAPLONG(shbp->byte_order_magic);
				shbp->major_version =
				    SWAPSHORT(shbp->major_version);
			}

			/*
			 * Make sure the byte order doesn't change;
			 * pcap_is_swapped() shouldn't change its
			 * return value in the middle of reading a capture.
			 */
			switch (shbp->byte_order_magic) {

			case BYTE_ORDER_MAGIC:
				/*
				 * OK.
				 */
				break;

			case SWAPLONG(BYTE_ORDER_MAGIC):
				/*
				 * Byte order changes.
				 */
				snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
				    "the file has sections with different byte orders");
				return (-1);

			default:
				/*
				 * Not a valid SHB.
				 */
				snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
				    "the file has a section with a bad byte order magic field");
				return (-1);
			}

			/*
			 * Make sure the major version is the version
			 * we handle.
			 */
			if (shbp->major_version != PCAP_NG_VERSION_MAJOR) {
				snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
				    "unknown pcapng savefile major version number %u",
				    shbp->major_version);
				return (-1);
			}

			/*
			 * Reset the interface count; this section should
			 * have its own set of IDBs.  If any of them
			 * don't have the same interface type, snapshot
			 * length, or resolution as the first interface
			 * we saw, we'll fail.  (And if we don't see
			 * any IDBs, we'll fail when we see a packet
			 * block.)
			 */
			ps->ifcount = 0;
			break;

		default:
			/*
			 * Not a packet block, IDB, or SHB; ignore it.
			 */
			break;
		}
	}

found:
	/*
	 * Is the interface ID an interface we know?
	 */
	if (interface_id >= ps->ifcount) {
		/*
		 * Yes.  Fail.
		 */
		snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
		    "a packet arrived on interface %u, but there's no Interface Description Block for that interface",
		    interface_id);
		return (-1);
	}

	if (hdr->caplen > (bpf_u_int32)p->snapshot) {
		snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
		    "invalid packet capture length %u, bigger than "
		    "snaplen of %d", hdr->caplen, p->snapshot);
		return (-1);
	}

	/*
	 * Convert the time stamp to seconds and fractions of a second,
	 * with the fractions being in units of the file-supplied resolution.
	 */
	sec = t / ps->ifaces[interface_id].tsresol + ps->ifaces[interface_id].tsoffset;
	frac = t % ps->ifaces[interface_id].tsresol;

	/*
	 * Convert the fractions from units of the file-supplied resolution
	 * to units of the user-requested resolution.
	 */
	switch (ps->ifaces[interface_id].scale_type) {

	case PASS_THROUGH:
		/*
		 * The interface resolution is what the user wants,
		 * so we're done.
		 */
		break;

	case SCALE_UP_DEC:
		/*
		 * The interface resolution is less than what the user
		 * wants; scale the fractional part up to the units of
		 * the resolution the user requested by multiplying by
		 * the quotient of the user-requested resolution and the
		 * file-supplied resolution.
		 *
		 * Those resolutions are both powers of 10, and the user-
		 * requested resolution is greater than the file-supplied
		 * resolution, so the quotient in question is an integer.
		 * We've calculated that quotient already, so we just
		 * multiply by it.
		 */
		frac *= ps->ifaces[interface_id].scale_factor;
		break;

	case SCALE_UP_BIN:
		/*
		 * The interface resolution is less than what the user
		 * wants; scale the fractional part up to the units of
		 * the resolution the user requested by multiplying by
		 * the quotient of the user-requested resolution and the
		 * file-supplied resolution.
		 *
		 * The file-supplied resolution is a power of 2, so the
		 * quotient is not an integer, so, in order to do this
		 * entirely with integer arithmetic, we multiply by the
		 * user-requested resolution and divide by the file-
		 * supplied resolution.
		 *
		 * XXX - Is there something clever we could do here,
		 * given that we know that the file-supplied resolution
		 * is a power of 2?  Doing a multiplication followed by
		 * a division runs the risk of overflowing, and involves
		 * two non-simple arithmetic operations.
		 */
		frac *= ps->user_tsresol;
		frac /= ps->ifaces[interface_id].tsresol;
		break;

	case SCALE_DOWN_DEC:
		/*
		 * The interface resolution is greater than what the user
		 * wants; scale the fractional part up to the units of
		 * the resolution the user requested by multiplying by
		 * the quotient of the user-requested resolution and the
		 * file-supplied resolution.
		 *
		 * Those resolutions are both powers of 10, and the user-
		 * requested resolution is less than the file-supplied
		 * resolution, so the quotient in question isn't an
		 * integer, but its reciprocal is, and we can just divide
		 * by the reciprocal of the quotient.  We've calculated
		 * the reciprocal of that quotient already, so we must
		 * divide by it.
		 */
		frac /= ps->ifaces[interface_id].scale_factor;
		break;


	case SCALE_DOWN_BIN:
		/*
		 * The interface resolution is greater than what the user
		 * wants; convert the fractional part to units of the
		 * resolution the user requested by multiplying by the
		 * quotient of the user-requested resolution and the
		 * file-supplied resolution.  We do that by multiplying
		 * by the user-requested resolution and dividing by the
		 * file-supplied resolution, as the quotient might not
		 * fit in an integer.
		 *
		 * The file-supplied resolution is a power of 2, so the
		 * quotient is not an integer, and neither is its
		 * reciprocal, so, in order to do this entirely with
		 * integer arithmetic, we multiply by the user-requested
		 * resolution and divide by the file-supplied resolution.
		 *
		 * XXX - Is there something clever we could do here,
		 * given that we know that the file-supplied resolution
		 * is a power of 2?  Doing a multiplication followed by
		 * a division runs the risk of overflowing, and involves
		 * two non-simple arithmetic operations.
		 */
		frac *= ps->user_tsresol;
		frac /= ps->ifaces[interface_id].tsresol;
		break;
	}
#ifdef _WIN32
	/*
	 * tv_sec and tv_used in the Windows struct timeval are both
	 * longs.
	 */
	hdr->ts.tv_sec = (long)sec;
	hdr->ts.tv_usec = (long)frac;
#else
	/*
	 * tv_sec in the UN*X struct timeval is a time_t; tv_usec is
	 * suseconds_t in UN*Xes that work the way the current Single
	 * UNIX Standard specify - but not all older UN*Xes necessarily
	 * support that type, so just cast to int.
	 */
	hdr->ts.tv_sec = (time_t)sec;
	hdr->ts.tv_usec = (int)frac;
#endif

	/*
	 * Get a pointer to the packet data.
	 */
	*data = get_from_block_data(&cursor, hdr->caplen, p->errbuf);
	if (*data == NULL)
		return (-1);

	pcap_post_process(p->linktype, p->swapped, hdr, *data);

	return (1);
}