libnetfilter_queue.c

/* libnetfilter_queue.c: generic library for access to nf_queue
 *
 * (C) 2005 by Harald Welte <laforge@gnumonks.org>
 * (C) 2005, 2008-2010 by Pablo Neira Ayuso <pablo@netfilter.org>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation (or any later at your option)
 *
 *  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *  2006-01-23 Andreas Florath <andreas@florath.net>
 *      Fix __set_verdict() that it can now handle payload.
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <time.h>
#include <errno.h>
#include <netinet/in.h>
#include <sys/socket.h>

#include <libnfnetlink/libnfnetlink.h>
#include <libnetfilter_queue/libnetfilter_queue.h>
#include "internal.h"

struct nfq_handle
{
        struct nfnl_handle *nfnlh;
        struct nfnl_subsys_handle *nfnlssh;
        struct nfq_q_handle *qh_list;
};

struct nfq_q_handle
{
        struct nfq_q_handle *next;
        struct nfq_handle *h;
        uint16_t id;

        nfq_callback *cb;
        void *data;
};

struct nfq_data {
        struct nfattr **data;
};

EXPORT_SYMBOL int nfq_errno;

/***********************************************************************
 * low level stuff
 ***********************************************************************/

static void del_qh(struct nfq_q_handle *qh)
{
        struct nfq_q_handle *cur_qh, *prev_qh = NULL;

        for (cur_qh = qh->h->qh_list; cur_qh; cur_qh = cur_qh->next) {
                if (cur_qh == qh) {
                        if (prev_qh)
                                prev_qh->next = qh->next;
                        else
                                qh->h->qh_list = qh->next;
                        return;
                }
                prev_qh = cur_qh;
        }
}

static void add_qh(struct nfq_q_handle *qh)
{
        qh->next = qh->h->qh_list;
        qh->h->qh_list = qh;
}

static struct nfq_q_handle *find_qh(struct nfq_handle *h, uint16_t id)
{
        struct nfq_q_handle *qh;

        for (qh = h->qh_list; qh; qh = qh->next) {
                if (qh->id == id)
                        return qh;
        }
        return NULL;
}

/* build a NFQNL_MSG_CONFIG message */
        static int
__build_send_cfg_msg(struct nfq_handle *h, uint8_t command,
                uint16_t queuenum, uint16_t pf)
{
        union {
                char buf[NFNL_HEADER_LEN
                        +NFA_LENGTH(sizeof(struct nfqnl_msg_config_cmd))];
                struct nlmsghdr nmh;
        } u;
        struct nfqnl_msg_config_cmd cmd;

        nfnl_fill_hdr(h->nfnlssh, &u.nmh, 0, AF_UNSPEC, queuenum,
                        NFQNL_MSG_CONFIG, NLM_F_REQUEST|NLM_F_ACK);

        cmd._pad = 0;
        cmd.command = command;
        cmd.pf = htons(pf);
        nfnl_addattr_l(&u.nmh, sizeof(u), NFQA_CFG_CMD, &cmd, sizeof(cmd));

        return nfnl_query(h->nfnlh, &u.nmh);
}

static int __nfq_rcv_pkt(struct nlmsghdr *nlh, struct nfattr *nfa[],
                void *data)
{
        struct nfgenmsg *nfmsg = NLMSG_DATA(nlh);
        struct nfq_handle *h = data;
        uint16_t queue_num = ntohs(nfmsg->res_id);
        struct nfq_q_handle *qh = find_qh(h, queue_num);
        struct nfq_data nfqa;

        if (!qh)
                return -ENODEV;

        if (!qh->cb)
                return -ENODEV;

        nfqa.data = nfa;

        return qh->cb(qh, nfmsg, &nfqa, qh->data);
}

/* public interface */

EXPORT_SYMBOL
struct nfnl_handle *nfq_nfnlh(struct nfq_handle *h)
{
        return h->nfnlh;
}

EXPORT_SYMBOL
int nfq_fd(struct nfq_handle *h)
{
        return nfnl_fd(nfq_nfnlh(h));
}
EXPORT_SYMBOL
struct nfq_handle *nfq_open(void)
{
        struct nfnl_handle *nfnlh = nfnl_open();
        struct nfq_handle *qh;

        if (!nfnlh)
                return NULL;

        /* unset netlink sequence tracking by default */
        nfnl_unset_sequence_tracking(nfnlh);

        qh = nfq_open_nfnl(nfnlh);
        if (!qh)
                nfnl_close(nfnlh);

        return qh;
}

EXPORT_SYMBOL
struct nfq_handle *nfq_open_nfnl(struct nfnl_handle *nfnlh)
{
        struct nfnl_callback pkt_cb = {
                .call           = __nfq_rcv_pkt,
                .attr_count     = NFQA_MAX,
        };
        struct nfq_handle *h;
        int err;

        h = malloc(sizeof(*h));
        if (!h)
                return NULL;

        memset(h, 0, sizeof(*h));
        h->nfnlh = nfnlh;

        h->nfnlssh = nfnl_subsys_open(h->nfnlh, NFNL_SUBSYS_QUEUE,
                                      NFQNL_MSG_MAX, 0);
        if (!h->nfnlssh) {
                /* FIXME: nfq_errno */
                goto out_free;
        }

        pkt_cb.data = h;
        err = nfnl_callback_register(h->nfnlssh, NFQNL_MSG_PACKET, &pkt_cb);
        if (err < 0) {
                nfq_errno = err;
                goto out_close;
        }

        return h;
out_close:
        nfnl_subsys_close(h->nfnlssh);
out_free:
        free(h);
        return NULL;
}

EXPORT_SYMBOL
int nfq_close(struct nfq_handle *h)
{
        int ret;

        ret = nfnl_close(h->nfnlh);
        if (ret == 0)
                free(h);
        return ret;
}

EXPORT_SYMBOL
int nfq_bind_pf(struct nfq_handle *h, uint16_t pf)
{
        return __build_send_cfg_msg(h, NFQNL_CFG_CMD_PF_BIND, 0, pf);
}

EXPORT_SYMBOL
int nfq_unbind_pf(struct nfq_handle *h, uint16_t pf)
{
        return __build_send_cfg_msg(h, NFQNL_CFG_CMD_PF_UNBIND, 0, pf);
}


EXPORT_SYMBOL
struct nfq_q_handle *nfq_create_queue(struct nfq_handle *h, uint16_t num,
                                      nfq_callback *cb, void *data)
{
        int ret;
        struct nfq_q_handle *qh;

        if (find_qh(h, num))
                return NULL;

        qh = malloc(sizeof(*qh));
        if (!qh)
                return NULL;

        memset(qh, 0, sizeof(*qh));
        qh->h = h;
        qh->id = num;
        qh->cb = cb;
        qh->data = data;

        ret = __build_send_cfg_msg(h, NFQNL_CFG_CMD_BIND, num, 0);
        if (ret < 0) {
                nfq_errno = ret;
                free(qh);
                return NULL;
        }

        add_qh(qh);
        return qh;
}

EXPORT_SYMBOL
int nfq_destroy_queue(struct nfq_q_handle *qh)
{
        int ret = __build_send_cfg_msg(qh->h, NFQNL_CFG_CMD_UNBIND, qh->id, 0);
        if (ret == 0) {
                del_qh(qh);
                free(qh);
        }

        return ret;
}

EXPORT_SYMBOL
int nfq_handle_packet(struct nfq_handle *h, char *buf, int len)
{
        return nfnl_handle_packet(h->nfnlh, buf, len);
}

EXPORT_SYMBOL
int nfq_set_mode(struct nfq_q_handle *qh, uint8_t mode, uint32_t range)
{
        union {
                char buf[NFNL_HEADER_LEN
                        +NFA_LENGTH(sizeof(struct nfqnl_msg_config_params))];
                struct nlmsghdr nmh;
        } u;
        struct nfqnl_msg_config_params params;

        nfnl_fill_hdr(qh->h->nfnlssh, &u.nmh, 0, AF_UNSPEC, qh->id,
                        NFQNL_MSG_CONFIG, NLM_F_REQUEST|NLM_F_ACK);

        params.copy_range = htonl(range);
        params.copy_mode = mode;
        nfnl_addattr_l(&u.nmh, sizeof(u), NFQA_CFG_PARAMS, &params,
                        sizeof(params));

        return nfnl_query(qh->h->nfnlh, &u.nmh);
}

EXPORT_SYMBOL
int nfq_set_queue_flags(struct nfq_q_handle *qh, uint32_t mask, uint32_t flags)
{
        union {
                char buf[NFNL_HEADER_LEN
                        +NFA_LENGTH(sizeof(mask)
                        +NFA_LENGTH(sizeof(flags)))];
                struct nlmsghdr nmh;
        } u;

        mask = htonl(mask);
        flags = htonl(flags);

        nfnl_fill_hdr(qh->h->nfnlssh, &u.nmh, 0, AF_UNSPEC, qh->id,
                      NFQNL_MSG_CONFIG, NLM_F_REQUEST|NLM_F_ACK);

        nfnl_addattr32(&u.nmh, sizeof(u), NFQA_CFG_FLAGS, flags);
        nfnl_addattr32(&u.nmh, sizeof(u), NFQA_CFG_MASK, mask);

        return nfnl_query(qh->h->nfnlh, &u.nmh);
}

EXPORT_SYMBOL
int nfq_set_queue_maxlen(struct nfq_q_handle *qh, uint32_t queuelen)
{
        union {
                char buf[NFNL_HEADER_LEN
                        +NFA_LENGTH(sizeof(struct nfqnl_msg_config_params))];
                struct nlmsghdr nmh;
        } u;
        uint32_t queue_maxlen = htonl(queuelen);

        nfnl_fill_hdr(qh->h->nfnlssh, &u.nmh, 0, AF_UNSPEC, qh->id,
                        NFQNL_MSG_CONFIG, NLM_F_REQUEST|NLM_F_ACK);

        nfnl_addattr_l(&u.nmh, sizeof(u), NFQA_CFG_QUEUE_MAXLEN, &queue_maxlen,
                        sizeof(queue_maxlen));

        return nfnl_query(qh->h->nfnlh, &u.nmh);
}

static int __set_verdict(struct nfq_q_handle *qh, uint32_t id,
                uint32_t verdict, uint32_t mark, int set_mark,
                uint32_t data_len, const unsigned char *data,
                enum nfqnl_msg_types type)
{
        struct nfqnl_msg_verdict_hdr vh;
        union {
                char buf[NFNL_HEADER_LEN
                        +NFA_LENGTH(sizeof(mark))
                        +NFA_LENGTH(sizeof(vh))];
                struct nlmsghdr nmh;
        } u;

        struct iovec iov[3];
        int nvecs;

        /* This must be declared here (and not inside the data
         * handling block) because the iovec points to this. */
        struct nfattr data_attr;

        memset(iov, 0, sizeof(iov));

        vh.verdict = htonl(verdict);
        vh.id = htonl(id);

        nfnl_fill_hdr(qh->h->nfnlssh, &u.nmh, 0, AF_UNSPEC, qh->id,
                                type, NLM_F_REQUEST);

        /* add verdict header */
        nfnl_addattr_l(&u.nmh, sizeof(u), NFQA_VERDICT_HDR, &vh, sizeof(vh));

        if (set_mark)
                nfnl_addattr32(&u.nmh, sizeof(u), NFQA_MARK, mark);

        iov[0].iov_base = &u.nmh;
        iov[0].iov_len = NLMSG_TAIL(&u.nmh) - (void *)&u.nmh;
        nvecs = 1;

        if (data_len) {
                /* The typecast here is to cast away data's const-ness: */
                nfnl_build_nfa_iovec(&iov[1], &data_attr, NFQA_PAYLOAD,
                                data_len, (unsigned char *) data);
                nvecs += 2;
                /* Add the length of the appended data to the message
                 * header.  The size of the attribute is given in the
                 * nfa_len field and is set in the nfnl_build_nfa_iovec()
                 * function. */
                u.nmh.nlmsg_len += data_attr.nfa_len;
        }

        return nfnl_sendiov(qh->h->nfnlh, iov, nvecs, 0);
}

EXPORT_SYMBOL
int nfq_set_verdict(struct nfq_q_handle *qh, uint32_t id,
                    uint32_t verdict, uint32_t data_len,
                    const unsigned char *buf)
{
        return __set_verdict(qh, id, verdict, 0, 0, data_len, buf,
                                                NFQNL_MSG_VERDICT);
}

EXPORT_SYMBOL
int nfq_set_verdict2(struct nfq_q_handle *qh, uint32_t id,
                     uint32_t verdict, uint32_t mark,
                     uint32_t data_len, const unsigned char *buf)
{
        return __set_verdict(qh, id, verdict, htonl(mark), 1, data_len,
                                                buf, NFQNL_MSG_VERDICT);
}

EXPORT_SYMBOL
int nfq_set_verdict_batch(struct nfq_q_handle *qh, uint32_t id,
                          uint32_t verdict)
{
        return __set_verdict(qh, id, verdict, 0, 0, 0, NULL,
                                        NFQNL_MSG_VERDICT_BATCH);
}

EXPORT_SYMBOL
int nfq_set_verdict_batch2(struct nfq_q_handle *qh, uint32_t id,
                           uint32_t verdict, uint32_t mark)
{
        return __set_verdict(qh, id, verdict, htonl(mark), 1, 0,
                                NULL, NFQNL_MSG_VERDICT_BATCH);
}

EXPORT_SYMBOL
int nfq_set_verdict_mark(struct nfq_q_handle *qh, uint32_t id,
                         uint32_t verdict, uint32_t mark,
                         uint32_t data_len, const unsigned char *buf)
{
        return __set_verdict(qh, id, verdict, mark, 1, data_len, buf,
                                                NFQNL_MSG_VERDICT);
}

/*************************************************************
 * Message parsing functions
 *************************************************************/

EXPORT_SYMBOL
struct nfqnl_msg_packet_hdr *nfq_get_msg_packet_hdr(struct nfq_data *nfad)
{
        return nfnl_get_pointer_to_data(nfad->data, NFQA_PACKET_HDR,
                                        struct nfqnl_msg_packet_hdr);
}

EXPORT_SYMBOL
uint32_t nfq_get_nfmark(struct nfq_data *nfad)
{
        return ntohl(nfnl_get_data(nfad->data, NFQA_MARK, uint32_t));
}

EXPORT_SYMBOL
int nfq_get_timestamp(struct nfq_data *nfad, struct timeval *tv)
{
        struct nfqnl_msg_packet_timestamp *qpt;
        qpt = nfnl_get_pointer_to_data(nfad->data, NFQA_TIMESTAMP,
                                        struct nfqnl_msg_packet_timestamp);
        if (!qpt)
                return -1;

        tv->tv_sec = __be64_to_cpu(qpt->sec);
        tv->tv_usec = __be64_to_cpu(qpt->usec);

        return 0;
}

EXPORT_SYMBOL
uint32_t nfq_get_indev(struct nfq_data *nfad)
{
        return ntohl(nfnl_get_data(nfad->data, NFQA_IFINDEX_INDEV, uint32_t));
}

EXPORT_SYMBOL
uint32_t nfq_get_physindev(struct nfq_data *nfad)
{
        return ntohl(nfnl_get_data(nfad->data, NFQA_IFINDEX_PHYSINDEV, uint32_t));
}

EXPORT_SYMBOL
uint32_t nfq_get_outdev(struct nfq_data *nfad)
{
        return ntohl(nfnl_get_data(nfad->data, NFQA_IFINDEX_OUTDEV, uint32_t));
}

EXPORT_SYMBOL
uint32_t nfq_get_physoutdev(struct nfq_data *nfad)
{
        return ntohl(nfnl_get_data(nfad->data, NFQA_IFINDEX_PHYSOUTDEV, uint32_t));
}

EXPORT_SYMBOL
int nfq_get_indev_name(struct nlif_handle *nlif_handle,
                       struct nfq_data *nfad, char *name)
{
        uint32_t ifindex = nfq_get_indev(nfad);
        return nlif_index2name(nlif_handle, ifindex, name);
}

EXPORT_SYMBOL
int nfq_get_physindev_name(struct nlif_handle *nlif_handle,
                           struct nfq_data *nfad, char *name)
{
        uint32_t ifindex = nfq_get_physindev(nfad);
        return nlif_index2name(nlif_handle, ifindex, name);
}

EXPORT_SYMBOL
int nfq_get_outdev_name(struct nlif_handle *nlif_handle,
                        struct nfq_data *nfad, char *name)
{
        uint32_t ifindex = nfq_get_outdev(nfad);
        return nlif_index2name(nlif_handle, ifindex, name);
}

EXPORT_SYMBOL
int nfq_get_physoutdev_name(struct nlif_handle *nlif_handle,
                            struct nfq_data *nfad, char *name)
{
        uint32_t ifindex = nfq_get_physoutdev(nfad);
        return nlif_index2name(nlif_handle, ifindex, name);
}

EXPORT_SYMBOL
struct nfqnl_msg_packet_hw *nfq_get_packet_hw(struct nfq_data *nfad)
{
        return nfnl_get_pointer_to_data(nfad->data, NFQA_HWADDR,
                                        struct nfqnl_msg_packet_hw);
}

EXPORT_SYMBOL
uint32_t nfq_get_skbinfo(struct nfq_data *nfad)
{
        if (!nfnl_attr_present(nfad->data, NFQA_SKB_INFO))
                return 0;

        return ntohl(nfnl_get_data(nfad->data, NFQA_SKB_INFO, uint32_t));
}

EXPORT_SYMBOL
int nfq_get_uid(struct nfq_data *nfad, uint32_t *uid)
{
        if (!nfnl_attr_present(nfad->data, NFQA_UID))
                return 0;

        *uid = ntohl(nfnl_get_data(nfad->data, NFQA_UID, uint32_t));
        return 1;
}

EXPORT_SYMBOL
int nfq_get_gid(struct nfq_data *nfad, uint32_t *gid)
{
        if (!nfnl_attr_present(nfad->data, NFQA_GID))
                return 0;

        *gid = ntohl(nfnl_get_data(nfad->data, NFQA_GID, uint32_t));
        return 1;
}

EXPORT_SYMBOL
int nfq_get_secctx(struct nfq_data *nfad, unsigned char **secdata)
{
        if (!nfnl_attr_present(nfad->data, NFQA_SECCTX))
                return -1;

        *secdata = (unsigned char *)nfnl_get_pointer_to_data(nfad->data,
                                                        NFQA_SECCTX, char);

        if (*secdata)
                return NFA_PAYLOAD(nfad->data[NFQA_SECCTX-1]);

        return 0;
}

EXPORT_SYMBOL
int nfq_get_payload(struct nfq_data *nfad, unsigned char **data)
{
        *data = (unsigned char *)
                nfnl_get_pointer_to_data(nfad->data, NFQA_PAYLOAD, char);
        if (*data)
                return NFA_PAYLOAD(nfad->data[NFQA_PAYLOAD-1]);

        return -1;
}

#define SNPRINTF_FAILURE(ret, rem, offset, len)                 \
do {                                                            \
        if (ret < 0)                                            \
                return ret;                                     \
        len += ret;                                             \
        if (ret > rem)                                          \
                ret = rem;                                      \
        offset += ret;                                          \
        rem -= ret;                                             \
} while (0)

EXPORT_SYMBOL
int nfq_snprintf_xml(char *buf, size_t rem, struct nfq_data *tb, int flags)
{
        struct nfqnl_msg_packet_hdr *ph;
        struct nfqnl_msg_packet_hw *hwph;
        uint32_t mark, ifi;
        uint32_t uid, gid;
        int size, offset = 0, len = 0, ret;
        unsigned char *data;

        size = snprintf(buf + offset, rem, "<pkt>");
        SNPRINTF_FAILURE(size, rem, offset, len);

        if (flags & NFQ_XML_TIME) {
                time_t t;
                struct tm tm;

                t = time(NULL);
                if (localtime_r(&t, &tm) == NULL)
                        return -1;

                size = snprintf(buf + offset, rem, "<when>");
                SNPRINTF_FAILURE(size, rem, offset, len);

                size = snprintf(buf + offset, rem,
                                "<hour>%d</hour>", tm.tm_hour);
                SNPRINTF_FAILURE(size, rem, offset, len);

                size = snprintf(buf + offset,
                                rem, "<min>%02d</min>", tm.tm_min);
                SNPRINTF_FAILURE(size, rem, offset, len);

                size = snprintf(buf + offset,
                                rem, "<sec>%02d</sec>", tm.tm_sec);
                SNPRINTF_FAILURE(size, rem, offset, len);

                size = snprintf(buf + offset, rem, "<wday>%d</wday>",
                                tm.tm_wday + 1);
                SNPRINTF_FAILURE(size, rem, offset, len);

                size = snprintf(buf + offset, rem, "<day>%d</day>", tm.tm_mday);
                SNPRINTF_FAILURE(size, rem, offset, len);

                size = snprintf(buf + offset, rem, "<month>%d</month>",
                                tm.tm_mon + 1);
                SNPRINTF_FAILURE(size, rem, offset, len);

                size = snprintf(buf + offset, rem, "<year>%d</year>",
                                1900 + tm.tm_year);
                SNPRINTF_FAILURE(size, rem, offset, len);

                size = snprintf(buf + offset, rem, "</when>");
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        ph = nfq_get_msg_packet_hdr(tb);
        if (ph) {
                size = snprintf(buf + offset, rem,
                                "<hook>%u</hook><id>%u</id>",
                                ph->hook, ntohl(ph->packet_id));
                SNPRINTF_FAILURE(size, rem, offset, len);

                hwph = nfq_get_packet_hw(tb);
                if (hwph && (flags & NFQ_XML_HW)) {
                        int i, hlen = ntohs(hwph->hw_addrlen);

                        size = snprintf(buf + offset, rem, "<hw><proto>%04x"
                                                           "</proto>",
                                        ntohs(ph->hw_protocol));
                        SNPRINTF_FAILURE(size, rem, offset, len);

                        size = snprintf(buf + offset, rem, "<src>");
                        SNPRINTF_FAILURE(size, rem, offset, len);

                        for (i=0; i<hlen; i++) {
                                size = snprintf(buf + offset, rem, "%02x",
                                                hwph->hw_addr[i]);
                                SNPRINTF_FAILURE(size, rem, offset, len);
                        }

                        size = snprintf(buf + offset, rem, "</src></hw>");
                        SNPRINTF_FAILURE(size, rem, offset, len);
                } else if (flags & NFQ_XML_HW) {
                        size = snprintf(buf + offset, rem, "<hw><proto>%04x"
                                                    "</proto></hw>",
                                 ntohs(ph->hw_protocol));
                        SNPRINTF_FAILURE(size, rem, offset, len);
                }
        }

        mark = nfq_get_nfmark(tb);
        if (mark && (flags & NFQ_XML_MARK)) {
                size = snprintf(buf + offset, rem, "<mark>%u</mark>", mark);
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        ifi = nfq_get_indev(tb);
        if (ifi && (flags & NFQ_XML_DEV)) {
                size = snprintf(buf + offset, rem, "<indev>%u</indev>", ifi);
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        ifi = nfq_get_outdev(tb);
        if (ifi && (flags & NFQ_XML_DEV)) {
                size = snprintf(buf + offset, rem, "<outdev>%u</outdev>", ifi);
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        ifi = nfq_get_physindev(tb);
        if (ifi && (flags & NFQ_XML_PHYSDEV)) {
                size = snprintf(buf + offset, rem,
                                "<physindev>%u</physindev>", ifi);
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        ifi = nfq_get_physoutdev(tb);
        if (ifi && (flags & NFQ_XML_PHYSDEV)) {
                size = snprintf(buf + offset, rem,
                                "<physoutdev>%u</physoutdev>", ifi);
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        if (nfq_get_uid(tb, &uid) && (flags & NFQ_XML_UID)) {
                size = snprintf(buf + offset, rem, "<uid>%u</uid>", uid);
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        if (nfq_get_gid(tb, &gid) && (flags & NFQ_XML_GID)) {
                size = snprintf(buf + offset, rem, "<gid>%u</gid>", gid);
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        ret = nfq_get_payload(tb, &data);
        if (ret >= 0 && (flags & NFQ_XML_PAYLOAD)) {
                int i;

                size = snprintf(buf + offset, rem, "<payload>");
                SNPRINTF_FAILURE(size, rem, offset, len);

                for (i=0; i<ret; i++) {
                        size = snprintf(buf + offset, rem, "%02x",
                                        data[i] & 0xff);
                        SNPRINTF_FAILURE(size, rem, offset, len);
                }

                size = snprintf(buf + offset, rem, "</payload>");
                SNPRINTF_FAILURE(size, rem, offset, len);
        }

        size = snprintf(buf + offset, rem, "</pkt>");
        SNPRINTF_FAILURE(size, rem, offset, len);

        return len;
}