Netfilter Netlink

Modules
	Conntrack
	Log
	Queue
Socket Creating
int	nfnl_connect (struct nl_sock *sk)
	Create and connect netfilter netlink socket.
Sending
int	nfnl_send_simple (struct nl_sock *sk, uint8_t subsys_id, uint8_t type, int flags, uint8_t family, uint16_t res_id)
	Send trivial netfilter netlink message.
Message Parsing
uint8_t	nfnlmsg_subsys (struct nlmsghdr *nlh)
	Get netfilter subsystem id from message.
uint8_t	nfnlmsg_subtype (struct nlmsghdr *nlh)
	Get netfilter message type from message.
uint8_t	nfnlmsg_family (struct nlmsghdr *nlh)
	Get netfilter family from message.
uint16_t	nfnlmsg_res_id (struct nlmsghdr *nlh)
	Get netfilter resource id from message.
Message Building
struct nl_msg *	nfnlmsg_alloc_simple (uint8_t subsys_id, uint8_t type, int flags, uint8_t family, uint16_t res_id)
	Allocate a new netfilter netlink message.
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)
	Add netlink and netfilter netlink headers to netlink message.

---

Detailed Description

Message Format

  <------- NLMSG_ALIGN(hlen) ------> <---- NLMSG_ALIGN(len) --->
 +----------------------------+- - -+- - - - - - - - - - -+- - -+
 |           Header           | Pad |       Payload       | Pad |
 |      struct nlmsghdr       |     |                     |     |
 +----------------------------+- - -+- - - - - - - - - - -+- - -+

  <-------- NFNL_HDRLEN --------->
 +--------------------------+- - -+------------+
 | Netfilter Netlink Header | Pad | Attributes |
 |    struct nfgenmsg       |     |            |
 +--------------------------+- - -+------------+
 nfnlmsg_attrdata(nfg, hdrlen)-----^

1) Creating a new netfilter netlink message

 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);

2) Sending of trivial messages

 // 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);

---

Function Documentation

int nfnl_connect

(

struct nl_sock *

sk

)

Parameters:

sk	Netlink socket.

Creates a NETLINK_NETFILTER netlink socket, binds the socket and issues a connection attempt.

See also:

nl_connect()

Returns:

0 on success or a negative error code.

Definition at line 84 of file nfnl.c.

References nl_connect().

int nfnl_send_simple	(	struct nl_sock *	sk,
		uint8_t	subsys_id,
		uint8_t	type,
		int	flags,
		uint8_t	family,
		uint16_t	res_id
	)

Parameters:

sk	Netlink socket.
subsys_id	nfnetlink subsystem
type	nfnetlink message type
flags	message flags
family	nfnetlink address family
res_id	nfnetlink resource id

Returns:

Newly allocated netlink message or NULL.

Definition at line 107 of file nfnl.c.

References nl_send_simple().

uint8_t nfnlmsg_subsys

(

struct nlmsghdr *

nlh

)

Parameters:

nlh	netlink messsage header

Definition at line 131 of file nfnl.c.

References nlmsghdr::nlmsg_type.

uint8_t nfnlmsg_subtype

(

struct nlmsghdr *

nlh

)

Parameters:

nlh	netlink messsage header

Definition at line 140 of file nfnl.c.

References nlmsghdr::nlmsg_type.

uint8_t nfnlmsg_family

(

struct nlmsghdr *

nlh

)

Parameters:

nlh	netlink messsage header

Definition at line 149 of file nfnl.c.

References nlmsg_data().

uint16_t nfnlmsg_res_id

(

struct nlmsghdr *

nlh

)

Parameters:

nlh	netlink messsage header

Definition at line 160 of file nfnl.c.

References nlmsg_data().

struct nl_msg* nfnlmsg_alloc_simple	(	uint8_t	subsys_id,
		uint8_t	type,
		int	flags,
		uint8_t	family,
		uint16_t	res_id
	)		[read]

Parameters:

subsys_id	nfnetlink subsystem
type	nfnetlink message type
flags	message flags
family	nfnetlink address family
res_id	nfnetlink resource id

Returns:

Newly allocated netlink message or NULL.

Definition at line 200 of file nfnl.c.

References nlmsg_alloc_simple(), and nlmsg_free().

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
	)

Parameters:

msg	netlink message
pid	netlink process id
seq	sequence number of message
subsys_id	nfnetlink subsystem
type	nfnetlink message type
flags	message flags
family	nfnetlink address family
res_id	nfnetlink resource id

Definition at line 230 of file nfnl.c.

References nlmsg_put().