nfnl.c

/* SPDX-License-Identifier: LGPL-2.1-only */
/*
 * Copyright (c) 2003-2012 Thomas Graf <tgraf@suug.ch>
 * Copyright (c) 2007 Philip Craig <philipc@snapgear.com>
 * Copyright (c) 2007 Secure Computing Corporation
 */
 
/**
 * @defgroup nfnl Netfilter Library (libnl-nf)
 *
 * @par Message Format
 * @code
 *  <------- NLMSG_ALIGN(hlen) ------> <---- NLMSG_ALIGN(len) --->
 * +----------------------------+- - -+- - - - - - - - - - -+- - -+
 * |           Header           | Pad |       Payload       | Pad |
 * |      struct nlmsghdr       |     |                     |     |
 * +----------------------------+- - -+- - - - - - - - - - -+- - -+
 * @endcode
 * @code
 *  <-------- NFNL_HDRLEN --------->
 * +--------------------------+- - -+------------+
 * | Netfilter Netlink Header | Pad | Attributes |
 * |    struct nfgenmsg       |     |            |
 * +--------------------------+- - -+------------+
 * nfnlmsg_attrdata(nfg, hdrlen)-----^
 * @endcode
 *
 * @par 1) Creating a new netfilter netlink message
 * @code
 * struct nl_msg *msg;
 *
 * // Create a new empty netlink message
 * msg = nlmsg_alloc();
 *
 * // Append the netlink and netfilter netlink message header
 * hdr = nfnlmsg_put(msg, PID, SEQ, SUBSYS, TYPE, NLM_F_ECHO,
 *                   FAMILY, RES_ID);
 *
 * // Append the attributes.
 * nla_put_u32(msg, 1, 0x10);
 *
 * // Message is ready to be sent.
 * nl_send_auto_complete(sk, msg);
 *
 * // All done? Free the message.
 * nlmsg_free(msg);
 * @endcode
 *
 * @par 2) Sending of trivial messages
 * @code
 * // For trivial messages not requiring any subsys specific header or
 * // attributes, nfnl_send_simple() may be used to send messages directly.
 * nfnl_send_simple(sk, SUBSYS, TYPE, 0, FAMILY, RES_ID);
 * @endcode
 * @{
 */
 
#include <netlink-private/netlink.h>
#include <netlink/netlink.h>
#include <netlink/netfilter/nfnl.h>
 
#include <linux/netfilter/nfnetlink.h>
 
/**
 * @name Socket Creating
 * @{
 */
 
/**
 * Create and connect netfilter netlink socket.
 * @arg sk              Netlink socket.
 *
 * Creates a NETLINK_NETFILTER netlink socket, binds the socket and
 * issues a connection attempt.
 *
 * @see nl_connect()
 *
 * @return 0 on success or a negative error code.
 */
int nfnl_connect(struct nl_sock *sk)
{
        return nl_connect(sk, NETLINK_NETFILTER);
}
 
/** @} */
 
/**
 * @name Sending
 * @{
 */
 
/**
 * Send trivial netfilter netlink message
 * @arg sk              Netlink socket.
 * @arg subsys_id       nfnetlink subsystem
 * @arg type            nfnetlink message type
 * @arg flags           message flags
 * @arg family          nfnetlink address family
 * @arg res_id          nfnetlink resource id
 *
 * @return 0 on success or a negative error code. Due to a bug, this function
 * returns the number of bytes sent. Treat any non-negative number as success.
 */
int nfnl_send_simple(struct nl_sock *sk, uint8_t subsys_id, uint8_t type,
                     int flags, uint8_t family, uint16_t res_id)
{
        struct nfgenmsg hdr = {
                .nfgen_family = family,
                .version = NFNETLINK_V0,
                .res_id = htons(res_id),
        };
 
        return nl_send_simple(sk, NFNLMSG_TYPE(subsys_id, type), flags,
                              &hdr, sizeof(hdr));
}
 
/** @} */
 
/**
 * @name Message Parsing
 * @{
 */
 
/**
 * Get netfilter subsystem id from message
 * @arg nlh     netlink messsage header
 */
uint8_t nfnlmsg_subsys(struct nlmsghdr *nlh)
{
        return NFNL_SUBSYS_ID(nlh->nlmsg_type);
}
 
/**
 * Get netfilter message type from message
 * @arg nlh     netlink messsage header
 */
uint8_t nfnlmsg_subtype(struct nlmsghdr *nlh)
{
        return NFNL_MSG_TYPE(nlh->nlmsg_type);
}
 
/**
 * Get netfilter family from message
 * @arg nlh     netlink messsage header
 */
uint8_t nfnlmsg_family(struct nlmsghdr *nlh)
{
        struct nfgenmsg *nfg = nlmsg_data(nlh);
 
        return nfg->nfgen_family;
}
 
/**
 * Get netfilter resource id from message
 * @arg nlh     netlink messsage header
 */
uint16_t nfnlmsg_res_id(struct nlmsghdr *nlh)
{
        struct nfgenmsg *nfg = nlmsg_data(nlh);
 
        return ntohs(nfg->res_id);
}
 
/** @} */
 
/**
 * @name Message Building
 * @{
 */
 
static int nfnlmsg_append(struct nl_msg *msg, uint8_t family, uint16_t res_id)
{
        struct nfgenmsg *nfg;
 
        nfg = nlmsg_reserve(msg, sizeof(*nfg), NLMSG_ALIGNTO);
        if (nfg == NULL)
                return -NLE_NOMEM;
 
        nfg->nfgen_family = family;
        nfg->version = NFNETLINK_V0;
        nfg->res_id = htons(res_id);
        NL_DBG(2, "msg %p: Added nfnetlink header family=%d res_id=%d\n",
               msg, family, res_id);
        return 0;
}
 
/**
 * Allocate a new netfilter netlink message
 * @arg subsys_id       nfnetlink subsystem
 * @arg type            nfnetlink message type
 * @arg flags           message flags
 * @arg family          nfnetlink address family
 * @arg res_id          nfnetlink resource id
 *
 * @return Newly allocated netlink message or NULL.
 */
struct nl_msg *nfnlmsg_alloc_simple(uint8_t subsys_id, uint8_t type, int flags,
                                    uint8_t family, uint16_t res_id)
{
        struct nl_msg *msg;
 
        msg = nlmsg_alloc_simple(NFNLMSG_TYPE(subsys_id, type), flags);
        if (msg == NULL)
                return NULL;
 
        if (nfnlmsg_append(msg, family, res_id) < 0)
                goto nla_put_failure;
 
        return msg;
 
nla_put_failure:
        nlmsg_free(msg);
        return NULL;
}
 
/**
 * Add netlink and netfilter netlink headers to netlink message
 * @arg msg             netlink message
 * @arg pid             netlink process id
 * @arg seq             sequence number of message
 * @arg subsys_id       nfnetlink subsystem
 * @arg type            nfnetlink message type
 * @arg flags           message flags
 * @arg family          nfnetlink address family
 * @arg res_id          nfnetlink resource id
 */
int nfnlmsg_put(struct nl_msg *msg, uint32_t pid, uint32_t seq,
                uint8_t subsys_id, uint8_t type, int flags, uint8_t family,
                uint16_t res_id)
{
        struct nlmsghdr *nlh;
 
        nlh = nlmsg_put(msg, pid, seq, NFNLMSG_TYPE(subsys_id, type), 0, flags);
        if (nlh == NULL)
                return -NLE_MSGSIZE;
 
        return nfnlmsg_append(msg, family, res_id);
}
 
/** @} */
 
/** @} */