pcap.c

Go to the documentation of this file.

/*
 *   This program is is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License, version 2 of the
 *   License as published by the Free Software Foundation.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/** Wrappers around libpcap functions
 *
 * @file src/lib/util/pcap.c
 *
 * @author Arran Cudbard-Bell (a.cudbardb@freeradius.org)
 * @copyright 2013 Arran Cudbard-Bell (a.cudbardb@freeradius.org)
 */
#ifdef HAVE_LIBPCAP
 
#include <freeradius-devel/util/debug.h>
#include <freeradius-devel/util/net.h>
#include <freeradius-devel/util/pair.h>
#include <freeradius-devel/util/pcap.h>
#include <freeradius-devel/util/syserror.h>
 
#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/uio.h>
 
#ifndef SIOCGIFHWADDR
#  include <ifaddrs.h>
#  ifdef HAVE_NET_IF_DL_H
#    include <net/if_dl.h>
#  endif
#else
#  include <net/if.h>
#endif
 
 
/** Talloc destructor to free pcap resources associated with a handle.
 *
 * @param pcap to free.
 * @return 0
 */
static int _free_pcap(fr_pcap_t *pcap)
{
        switch (pcap->type) {
        case PCAP_INTERFACE_IN:
        case PCAP_INTERFACE_OUT:
        case PCAP_INTERFACE_IN_OUT:
        case PCAP_FILE_IN:
        case PCAP_STDIO_IN:
                if (pcap->handle) {
                        pcap_close(pcap->handle);
 
                        if (pcap->fd > 0) {
                                close(pcap->fd);
                        }
                }
                break;
 
        case PCAP_FILE_OUT:
        case PCAP_STDIO_OUT:
                if (pcap->dumper) {
                        pcap_dump_flush(pcap->dumper);
                        pcap_dump_close(pcap->dumper);
                }
                break;
 
        case PCAP_INVALID:
                break;
        }
 
        return 0;
}
 
/** Get data link from pcap_if_t
 *
 * libpcap requires an open pcap handle to get data_link type
 * unfortunately when we're trying to find useful interfaces
 * this is too late.
 *
 * @param dev to get link layer for.
 * @return
 *      - Datalink layer.
 *      - -1 on failure.
 */
int fr_pcap_if_link_layer(pcap_if_t *dev)
{
        char    errbuf[PCAP_ERRBUF_SIZE];
        pcap_t  *pcap;
        int     data_link;
 
        pcap = pcap_open_live(dev->name, 0, 0, 0, errbuf);
        if (!pcap) {
                fr_strerror_printf("%s", errbuf);
                return -1;
        }
 
        data_link = pcap_datalink(pcap);
        pcap_close(pcap);
 
        return data_link;
}
 
/** Initialise a pcap handle abstraction
 *
 * @param ctx talloc TALLOC_CTX to allocate handle in.
 * @param name of interface or file to open.
 * @param type of handle to initialise.
 * @return new handle or NULL on error.
 */
fr_pcap_t *fr_pcap_init(TALLOC_CTX *ctx, char const *name, fr_pcap_type_t type)
{
        fr_pcap_t       *this;
 
        if (!fr_cond_assert(type >= PCAP_INTERFACE_IN && type <= PCAP_INTERFACE_IN_OUT)) {
                fr_strerror_printf("Invalid PCAP type: %d", type);
                return NULL;
        }
 
        this = talloc_zero(ctx, fr_pcap_t);
        if (!this) return NULL;
 
        talloc_set_destructor(this, _free_pcap);
        this->name = talloc_typed_strdup(this, name);
        this->type = type;
        this->link_layer = -1;
 
        return this;
}
 
/** Get MAC address for given interface
 *
 * @param[out] macaddr to write MAC address to.
 * @param[in] ifname to get MAC for.
 * @return
 *      - 0 on success.
 *      - -1 on error.
 */
int fr_pcap_mac_addr(uint8_t *macaddr, char *ifname)
{
#ifndef SIOCGIFHWADDR
        struct ifaddrs *ifap, *ifaptr;
        unsigned char *ptr;
 
        if (getifaddrs(&ifap) == 0) {
                for (ifaptr = ifap; ifaptr != NULL; ifaptr = (ifaptr)->ifa_next) {
                        if (!strcmp((ifaptr)->ifa_name, ifname) && (((ifaptr)->ifa_addr)->sa_family == AF_LINK)) {
                                ptr = (uint8_t *)LLADDR((struct sockaddr_dl *)(ifaptr)->ifa_addr);
                                memcpy(macaddr, ptr, ETHER_ADDR_LEN);
                                break;
                        }
                }
                freeifaddrs(ifap);
                return (ifaptr != NULL ? 0 : -1);
        }
        return -1;
#else
        int fd, ret;
        struct ifreq ifr;
 
        fd = socket(AF_INET, SOCK_DGRAM, 0);
 
        if (fd < 0) {
                return -1;
        }
 
        ifr.ifr_addr.sa_family = AF_INET;
        strlcpy(ifr.ifr_name, ifname , IFNAMSIZ-1);
 
        ret = ioctl(fd, SIOCGIFHWADDR, &ifr);
 
        close(fd);
 
        if (ret == 0) {
                memcpy(macaddr, (uint8_t *)ifr.ifr_hwaddr.sa_data, ETHER_ADDR_LEN);
                return 0;
        }
        return -1;
#endif
}
 
/** Open a PCAP handle abstraction
 *
 * This opens interfaces for capture or injection, or files/streams for reading/writing.
 * @param pcap created with fr_pcap_init.
 * @return
 *      - 0 on success.
 *      - -1 on failure.
 */
int fr_pcap_open(fr_pcap_t *pcap)
{
        switch (pcap->type) {
        case PCAP_INTERFACE_OUT:
        case PCAP_INTERFACE_IN:
        case PCAP_INTERFACE_IN_OUT:
        {
                /*
                 *      Also has the pleasant side effect of not allowing
                 *      handles to be opened on "any".
                 *
                 *      We do this first, as it's the most specific error.
                 */
                pcap->ifindex = if_nametoindex(pcap->name);
                if (!pcap->ifindex) {
                        fr_strerror_printf("Unknown interface \"%s\"", pcap->name);
                        return -1;
                }
 
#if defined(HAVE_PCAP_CREATE) && defined(HAVE_PCAP_ACTIVATE)
                pcap->handle = pcap_create(pcap->name, pcap->errbuf);
                if (!pcap->handle) {
                        fr_strerror_printf("%s", pcap->errbuf);
                        return -1;
                }
                if (pcap_set_snaplen(pcap->handle, SNAPLEN) != 0) {
                create_error:
                        fr_strerror_printf("%s", pcap_geterr(pcap->handle));
                        pcap_close(pcap->handle);
                        pcap->handle = NULL;
                        return -1;
                }
                if (pcap_set_timeout(pcap->handle, PCAP_NONBLOCK_TIMEOUT) != 0) {
                        goto create_error;
                }
                if (pcap_set_promisc(pcap->handle, pcap->promiscuous) != 0) {
                        goto create_error;
                }
 
                if (pcap_set_buffer_size(pcap->handle, SNAPLEN *
                                         (pcap->buffer_pkts ? pcap->buffer_pkts : PCAP_BUFFER_DEFAULT)) != 0) {
                        goto create_error;
                }
                if (pcap_activate(pcap->handle) != 0) {
                        goto create_error;
                }
#else
                /*
                 *      Alternative functions for libpcap < 1.0
                 */
                pcap->handle = pcap_open_live(pcap->name, SNAPLEN, pcap->promiscuous, PCAP_NONBLOCK_TIMEOUT,
                                              pcap->errbuf);
                if (!pcap->handle) {
                        fr_strerror_printf("%s", pcap->errbuf);
                        return -1;
                }
#endif
 
                /*
                 *      Do this later so we get real errors from libpcap,
                 *      when bad interfaces are passed in.
                 */
                if (fr_pcap_mac_addr((uint8_t *)&pcap->ether_addr, pcap->name) != 0) {
                        fr_strerror_printf("Couldn't get MAC address for interface %s", pcap->name);
                        pcap_close(pcap->handle);
                        return -1;
                }
 
                /*
                 *      Despite accepting an errbuff, pcap_setnonblock doesn't seem to write
                 *      error message there in newer versions.
                 */
                if (pcap_setnonblock(pcap->handle, true, pcap->errbuf) != 0) {
                        fr_strerror_printf("%s", *pcap->errbuf != '\0' ?
                                           pcap->errbuf : pcap_geterr(pcap->handle));
                        pcap_close(pcap->handle);
                        pcap->handle = NULL;
                        return -1;
                }
 
                pcap->fd = pcap_get_selectable_fd(pcap->handle);
                pcap->link_layer = pcap_datalink(pcap->handle);
#ifndef __linux__
                {
                        int value = 1;
                        if (ioctl(pcap->fd, BIOCIMMEDIATE, &value) < 0) {
                                fr_strerror_printf("Failed setting BIOCIMMEDIATE: %s", fr_syserror(errno));
                        }
                }
#endif
        }
                break;
 
        case PCAP_FILE_IN:
                pcap->handle = pcap_open_offline(pcap->name, pcap->errbuf);
                if (!pcap->handle) {
                        fr_strerror_printf("%s", pcap->errbuf);
 
                        return -1;
                }
                pcap->fd = pcap_get_selectable_fd(pcap->handle);
                pcap->link_layer = pcap_datalink(pcap->handle);
                break;
 
        case PCAP_FILE_OUT:
                if (pcap->link_layer < 0) {
                        pcap->link_layer = DLT_EN10MB;
                }
                pcap->handle = pcap_open_dead(pcap->link_layer, SNAPLEN);
                if (!pcap->handle) {
                        fr_strerror_const("Unknown error occurred opening dead PCAP handle");
 
                        return -1;
                }
                pcap->dumper = pcap_dump_open(pcap->handle, pcap->name);
                if (!pcap->dumper) {
                        fr_strerror_printf("%s", pcap_geterr(pcap->handle));
 
                        return -1;
                }
                break;
 
#ifdef HAVE_PCAP_FOPEN_OFFLINE
        case PCAP_STDIO_IN:
                pcap->handle = pcap_fopen_offline(stdin, pcap->errbuf);
                if (!pcap->handle) {
                        fr_strerror_printf("%s", pcap->errbuf);
 
                        return -1;
                }
                pcap->fd = pcap_get_selectable_fd(pcap->handle);
                pcap->link_layer = pcap_datalink(pcap->handle);
                break;
#else
        case PCAP_STDIO_IN:
                fr_strerror_const("This version of libpcap does not support reading pcap data from streams");
 
                return -1;
#endif
#ifdef HAVE_PCAP_DUMP_FOPEN
        case PCAP_STDIO_OUT:
                pcap->handle = pcap_open_dead(DLT_EN10MB, SNAPLEN);
                pcap->dumper = pcap_dump_fopen(pcap->handle, stdout);
                if (!pcap->dumper) {
                        fr_strerror_printf("%s", pcap_geterr(pcap->handle));
 
                        return -1;
                }
                break;
#else
        case PCAP_STDIO_OUT:
                fr_strerror_const("This version of libpcap does not support writing pcap data to streams");
 
                return -1;
#endif
        case PCAP_INVALID:
        default:
                (void)fr_cond_assert(0);
                fr_strerror_printf("Bad handle type (%i)", pcap->type);
                return -1;
        }
 
        return 0;
}
 
/** Apply capture filter to an interface
 *
 * @param pcap handle to apply filter to.
 * @param expression PCAP expression to use as a filter.
 * @return
 *      - 0 on success.
 *      - 1 can't apply to interface.
 *      - -1 on failure.
 */
int fr_pcap_apply_filter(fr_pcap_t *pcap, char const *expression)
{
        bpf_u_int32 mask = 0;           /* Our netmask */
        bpf_u_int32 net = 0;            /* Our IP */
        struct bpf_program fp;
 
        /*
         *      nflog devices are in the set of devices selected by default.
         *      Unfortunately there's a bug in all released version of libpcap (as of 2/1/2014)
         *      which triggers an abort if pcap_setfilter is called on an nflog interface.
         *
         *      See here:
         *      https://github.com/the-tcpdump-group/libpcap/commit/676cf8a61ed240d0a86d471ef419f45ba35dba80
         */
#ifdef DLT_NFLOG
        if (pcap->link_layer == DLT_NFLOG) {
                fr_strerror_const("NFLOG link-layer type filtering not implemented");
 
                return 1;
        }
#endif
 
        if (pcap->type == PCAP_INTERFACE_IN || pcap->type == PCAP_INTERFACE_IN_OUT) {
                if (pcap_lookupnet(pcap->name, &net, &mask, pcap->errbuf) < 0) {
                        fr_strerror_printf("Failed getting IP for interface \"%s\", using defaults: %s",
                                           pcap->name, pcap->errbuf);
                }
        }
 
        if (pcap_compile(pcap->handle, &fp, expression, 0, net) < 0) {
                fr_strerror_printf("%s", pcap_geterr(pcap->handle));
 
                return -1;
        }
 
        if (pcap_setfilter(pcap->handle, &fp) < 0) {
                pcap_freecode(&fp);
 
                fr_strerror_printf("%s", pcap_geterr(pcap->handle));
                return -1;
        }
 
        pcap_freecode(&fp);     /* Free the filter, it's not longer needed after its been applied */
 
        return 0;
}
 
/** Retrieve list of interface names that will be used for capture.
 * Only used for debugging.
 *
 * @param ctx talloc context for allicating string.
 * @param pcap handle list.
 * @param c separator to use for list.
 * @return
 *      - string buffer.
 */
char *fr_pcap_device_names(TALLOC_CTX *ctx, fr_pcap_t *pcap, char c)
{
        fr_pcap_t *pcap_p;
        char *buff, *p, *end;
        size_t len = 0;
 
        if (!pcap) {
        null:
                return talloc_zero_array(ctx, char, 1);
        }
 
        for (pcap_p = pcap;
             pcap_p;
             pcap_p = pcap_p->next) {
                /*
                 *      talloc_array_length includes \0 which accounts for c
                 */
                len += talloc_array_length(pcap_p->name);
        }
 
        if (!len) goto null;
 
        buff = p = talloc_zero_array(ctx, char, len);
        end = p + len;
 
        for (pcap_p = pcap;
             pcap_p;
             pcap_p = pcap_p->next) {
                size_t name_len = talloc_array_length(pcap_p->name) - 1;
 
                if (!fr_cond_assert(p < end)) {
                        talloc_free(buff);
                        return NULL;
                }
 
                memcpy(p, pcap_p->name, name_len);
                p += name_len;
                *p++ = c;
        }
        *(end - 1) = '\0';      /* Strip trailing separation char */
 
        return buff;
}
 
 
/** Check whether fr_pcap_link_layer_offset can process a link_layer
 *
 * @param link_layer to check.
 * @return
 *      - true if supported.
 *      - false if not supported.
 */
bool fr_pcap_link_layer_supported(int link_layer)
{
        switch (link_layer) {
        case DLT_EN10MB:
        case DLT_RAW:
        case DLT_NULL:
        case DLT_LOOP:
#ifdef DLT_LINUX_SLL
        case DLT_LINUX_SLL:
#endif
        case DLT_PFLOG:
                return true;
 
        default:
                return false;
        }
}
 
/** Returns the length of the link layer header
 *
 * Libpcap does not include a decoding function to skip the L2 header, but it does
 * at least inform us of the type.
 *
 * Unfortunately some headers are of variable length (like ethernet), so additional
 * decoding logic is required.
 *
 * @note No header data is returned, this is only meant to be used to determine how
 * data to consume before attempting to parse the IP header.
 *
 * @param data start of packet data.
 * @param len caplen.
 * @param link_layer value returned from pcap_linktype.
 * @return
 *      - Length of the header.
 *      - -1 on failure.
 */
ssize_t fr_pcap_link_layer_offset(uint8_t const *data, size_t len, int link_layer)
{
        uint8_t const *p = data;
 
        switch (link_layer) {
        case DLT_RAW:
                break;
 
        case DLT_NULL:
        case DLT_LOOP:
                p += 4;
                if (((size_t)(p - data)) > len) {
                ood:
                        fr_strerror_printf("Out of data, needed %zu bytes, have %zu bytes",
                                           (size_t)(p - data), len);
                        return -1;
                }
                break;
 
        case DLT_EN10MB:
        {
                uint16_t ether_type;    /* Ethernet type */
                int i;
 
                p += 12;                /* SRC/DST Mac-Addresses */
                if (((size_t)(p - data)) > len) {
                        goto ood;
                }
 
                for (i = 0; i < 3; i++) {
                        ether_type = ntohs(*((uint16_t const *) p));
                        switch (ether_type) {
                        /*
                         *      There are a number of devices out there which
                         *      double tag with 0x8100 *sigh*
                         */
                        case 0x8100:    /* CVLAN */
                        case 0x9100:    /* SVLAN */
                        case 0x9200:    /* SVLAN */
                        case 0x9300:    /* SVLAN */
                                p += 4;
                                if (((size_t)(p - data)) > len) {
                                        goto ood;
                                }
                                break;
 
                        default:
                                p += 2;
                                if (((size_t)(p - data)) > len) {
                                        goto ood;
                                }
                                goto done;
                        }
                }
                fr_strerror_const("Exceeded maximum level of VLAN tag nesting (2)");
                return -1;
        }
 
#ifdef DLT_LINUX_SLL
        case DLT_LINUX_SLL:
                p += 16;
                if (((size_t)(p - data)) > len) {
                        goto ood;
                }
                break;
#endif
 
        case DLT_PFLOG:
                p += 28;
                if (((size_t)(p - data)) > len) {
                        goto ood;
                }
                break;
 
        default:
                fr_strerror_printf("Unsupported link layer type %i", link_layer);
                return -1;
        }
 
done:
        return p - data;
}
#endif  /* HAVE_LIBPCAP */