Read the magic number into a byte array.

[libpcap] / sf-pcapng.c

/*
 * 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-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

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,
 * 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 {
        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 */
                        pcap_snprintf(errbuf, PCAP_ERRBUF_SIZE,
                            "truncated dump file; tried to read %" PRIsize " bytes, only got %" PRIsize,
                            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)) {
                pcap_snprintf(errbuf, PCAP_ERRBUF_SIZE,
                    "block in pcapng dump file has a length of %u < %" PRIsize,
                    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.
                 */
                pcap_snprintf(errbuf, PCAP_ERRBUF_SIZE,
                    "block in pcapng dump file has a length of %u that is not a multiple of 4" PRIsize,
                    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) {
                        pcap_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) {
                        pcap_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.
                 */
                pcap_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) {
                pcap_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) {
                                pcap_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) {
                                pcap_snprintf(errbuf, PCAP_ERRBUF_SIZE,
                                    "Interface Description Block has if_tsresol option with length %u != 1",
                                    opthdr->option_length);
                                return (-1);
                        }
                        if (saw_tsresol) {
                                pcap_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.
                                         */
                                        pcap_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).
                                         */
                                        pcap_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) {
                                pcap_snprintf(errbuf, PCAP_ERRBUF_SIZE,
                                    "Interface Description Block has if_tsoffset option with length %u != 8",
                                    opthdr->option_length);
                                return (-1);
                        }
                        if (saw_tsoffset) {
                                pcap_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 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.
                                 */
                                pcap_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).
                                 */
                                pcap_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.
                         */
                        pcap_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;
        }

        /*
         * 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)) {
                pcap_snprintf(errbuf, PCAP_ERRBUF_SIZE,
                    "Section Header Block in pcapng dump file has a length of %u < %" PRIsize,
                    total_length,
                    sizeof(*bhdrp) + sizeof(*shbp) + sizeof(struct block_trailer));
                *err = 1;
                return (NULL);
        }

        /*
         * Make sure it's not too big.
         */
        if (total_length > INITIAL_MAX_BLOCKSIZE) {
                pcap_snprintf(errbuf, PCAP_ERRBUF_SIZE,
                    "pcapng block size %u > maximum %u",
                    total_length, INITIAL_MAX_BLOCKSIZE);
                *err = 1;
                return (NULL);
        }

        /*
         * OK, this is a good pcapng file.
         * Allocate a pcap_t for it.
         */
        p = pcap_open_offline_common(errbuf, sizeof (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:
                pcap_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) {
                pcap_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 version 1.0 is supported */
        if (! (shbp->major_version == PCAP_NG_VERSION_MAJOR &&
               shbp->minor_version == PCAP_NG_VERSION_MINOR)) {
                pcap_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 */
                        pcap_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, &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.
                         */
                        pcap_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->snapshot = idbp->snaplen;
        if (p->snapshot <= 0) {
                /*
                 * Bogus snapshot length; use the maximum for this
                 * link-layer type as a fallback.
                 *
                 * XXX - the only reason why snapshot is signed is
                 * that pcap_snapshot() returns an int, not an
                 * unsigned int.
                 */
                p->snapshot = max_snaplen_for_dlt(idbp->linktype);
        }
        p->linktype = linktype_to_dlt(idbp->linktype);
        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 0 on success, 1
 * 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 (1);     /* 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) {
                                pcap_snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
                                    "an interface has a type %u different from the type of the first interface",
                                    idbp->linktype);
                                return (-1);
                        }
                        if ((bpf_u_int32)p->snapshot != idbp->snaplen) {
                                pcap_snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
                                    "an interface has a snapshot length %u different from the type of the first interface",
                                    idbp->snaplen);
                                return (-1);
                        }

                        /*
                         * Try to add this interface.
                         */
                        if (!add_interface(p, &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.
                                 */
                                pcap_snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
                                    "the file has sections with different byte orders");
                                return (-1);

                        default:
                                /*
                                 * Not a valid SHB.
                                 */
                                pcap_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) {
                                pcap_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.
                 */
                pcap_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) {
                pcap_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);

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

        return (0);
}