Modules

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  ) 

Create and connect netfilter netlink socket.

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().

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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.

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().

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uint8_t nfnlmsg_subsys ( struct nlmsghdr *  nlh  ) 

Get netfilter subsystem id from message.

Parameters:
nlh netlink messsage header

Definition at line 131 of file nfnl.c.

uint8_t nfnlmsg_subtype ( struct nlmsghdr *  nlh  ) 

Get netfilter message type from message.

Parameters:
nlh netlink messsage header

Definition at line 140 of file nfnl.c.

uint8_t nfnlmsg_family ( struct nlmsghdr *  nlh  ) 

Get netfilter family from message.

Parameters:
nlh netlink messsage header

Definition at line 149 of file nfnl.c.

References nlmsg_data().

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uint16_t nfnlmsg_res_id ( struct nlmsghdr *  nlh  ) 

Get netfilter resource id from message.

Parameters:
nlh netlink messsage header

Definition at line 160 of file nfnl.c.

References nlmsg_data().

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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 
) [read]

Allocate a new netfilter netlink message.

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().

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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.

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().

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