Netfilter Netlink

Collaboration diagram for Netfilter Netlink:

Modules
	Conntrack object handling
	Log
	nf_tables
	Queue

Socket Creating
int	nfnl_connect (struct nl_sock *sk)
	Create and connect netfilter netlink socket. More...

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. More...

Message Parsing
uint8_t	nfnlmsg_subsys (struct nlmsghdr *nlh)
	Get netfilter subsystem id from message. More...
uint8_t	nfnlmsg_subtype (struct nlmsghdr *nlh)
	Get netfilter message type from message. More...
uint8_t	nfnlmsg_family (struct nlmsghdr *nlh)
	Get netfilter family from message. More...
uint16_t	nfnlmsg_res_id (struct nlmsghdr *nlh)
	Get netfilter resource id from message. More...

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. More...
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. More...

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

)

Create and connect netfilter netlink socket.

• 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.

References NETLINK_NETFILTER, and nl_connect().

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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.

• 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.

References nfgenmsg::nfgen_family, NFNETLINK_V0, NFNLMSG_TYPE, and nl_send_simple().

Referenced by nfnl_ct_dump_request(), nfnl_nft_chain_dump_request(), nfnl_nft_rule_dump_request(), and nfnl_nft_table_dump_request().

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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.

• 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.

References NFNLMSG_TYPE, nlmsg_alloc_simple(), nlmsg_free(), and NULL.

Referenced by nfnl_queue_msg_build_verdict().

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uint8_t nfnlmsg_family

(

struct nlmsghdr *

nlh

)

Get netfilter family from message.

• nlh netlink messsage header

References nfgenmsg::nfgen_family, and nlmsg_data().

Referenced by nfnlmsg_ct_parse(), nfnlmsg_log_msg_parse(), nfnlmsg_nft_chain_parse(), nfnlmsg_nft_rule_parse(), nfnlmsg_nft_set_parse(), nfnlmsg_nft_table_parse(), and nfnlmsg_queue_msg_parse().

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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.

• 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

References NFNLMSG_TYPE, NLE_MSGSIZE, nlh, nlmsg_put(), and NULL.

Referenced by nfnl_nft_set_dump_request(), and nfnl_nft_setelem_dump_request().

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uint16_t nfnlmsg_res_id

(

struct nlmsghdr *

nlh

)

Get netfilter resource id from message.

• nlh netlink messsage header

References nlmsg_data(), and nfgenmsg::res_id.

Referenced by nfnlmsg_queue_msg_parse().

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uint8_t nfnlmsg_subsys

(

struct nlmsghdr *

nlh

)

Get netfilter subsystem id from message.

• nlh netlink messsage header

References NFNL_SUBSYS_ID, and nlmsghdr::nlmsg_type.

uint8_t nfnlmsg_subtype

(

struct nlmsghdr *

nlh

)

Get netfilter message type from message.

• nlh netlink messsage header

References NFNL_MSG_TYPE, and nlmsghdr::nlmsg_type.

Referenced by nfnlmsg_ct_group().

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