www.pudn.com > src.rar > libnids.3
.\" libnids manpage by Dug Song
.\" tmac.an sux, tmac.doc rules
.TH LIBNIDS 3
.SH NAME
libnids \- network intrusion detection system E-box library
.SH SYNOPSIS
.nf
#include
extern struct nids_prm \fInids_params\fR;
extern char \fInids_errbuf\fR[];
int
\fBnids_init\fR(void);
void
\fBnids_register_ip_frag\fR(void (*ip_frag_func)(struct ip *pkt));
void
\fBnids_register_ip\fR(void (*ip_func)(struct ip *pkt));
void
\fBnids_register_udp\fR(void (*udp_func)(struct tuple4 *addr, u_char *data, int len, struct ip *pkt));
void
\fBnids_register_tcp\fR(void (*tcp_func)(struct tcp_stream *ts, void **param));
void
\fBnids_killtcp\fR(struct tcp_stream *ts);
void
\fBnids_discard\fR(struct tcp_stream *ts, int numbytes);
void
\fBnids_run\fR(void);
int
\fBnids_next\fR(void);
int
\fBnids_getfd\fR(void);
.fi
.SH DESCRIPTION
.B libnids
provides the functionality of a network intrusion detection system
(NIDS) E-box component. It currently performs:
.LP
.nf
1. IP defragmentation
2. TCP stream reassembly
3. TCP port scan detection
.fi
.PP
.B libnids
performs TCP/IP reassembly in exactly the same way as Linux
2.0.36 kernels, and correctly handles all of the attacks implemented
in fragrouter(8) (plus many other attacks as well).
.SH ROUTINES
.PP
.BR nids_init ()
initializes the application for sniffing, based on the values set in the
global variable \fInids_params\fR, declared as follows:
.LP
.nf
struct nids_prm {
int n_tcp_streams;
int n_hosts;
char *device;
int sk_buff_size;
int dev_addon;
void (*syslog)(int type, int err, struct ip *iph, void *data);
int syslog_level;
int scan_num_hosts;
int scan_num_ports;
int scan_delay;
void (*no_mem)(void);
int (*ip_filter)(struct ip *iph);
char *pcap_filter;
int promisc;
int one_loop_less;
} nids_params;
.fi
.PP
The members of this structure are:
.TP
.I n_tcp_streams
Size of the hash table used for storing TCP connection information (
a maximum of 3/4 * \fIn_tcp_streams\fR TCP connections will be
followed simultaneously). Default value: 1024
.TP
.I n_hosts
Size of the hash table used for storing IP defragmentation
information. Default value: 256
.TP
.I filename
It this variable is set, libnids will call pcap_open_offline with this
variable as the argument (instead of pcap_open_live()). Default value: NULL
.TP
.I device
Interface to monitor. Default value: NULL (in which case an
appropriate device is determined automatically). If this variable is assigned
value \fBall\fR, libnids will attempt to capture packets on all interfaces
(which works on Linux only)
.TP
.I sk_buff_size
Size of \fIstruct sk_buff\fR (used for queuing packets), which should
be set to match the value on the hosts being monitored. Default value: 168
.TP
.I dev_addon
Number of bytes in \fIstruct sk_buff\fR reserved for link-layer
information. Default value: -1 (in which case an appropriate offset if
determined automatically based on link-layer type)
.TP
.I syslog
Syslog callback function, used to report unusual conditions, such as
port scan attempts, invalid TCP header flags, etc. Default value:
\fInids_syslog\fR (which logs messages via syslog(3) without regard
for message rate per second or free disk space)
.TP
.I syslog_level
Log level used by \fInids_syslog\fR for reporting events via
syslog(3). Default value: LOG_ALERT
.TP
.I scan_num_hosts
Size of hash table used for storing portscan information (the maximum
number portscans that will be detected simultaneously). If set to 0,
portscan detection will be disabled. Default value: 256
.TP
.I scan_num_ports
Minimum number of ports that must be scanned from the same source
host before it is identifed as a portscan. Default value: 10
.TP
.I scan_delay
Maximum delay (in milliseconds) between connections to different
ports for them to be identified as part of a portscan. Default value:
3000
.TP
.I no_mem
Out-of-memory callback function, used to terminate the calling process
gracefully.
.TP
.I ip_filter
IP filtering callback function, used to selectively discard IP
packets, inspected after reassembly. If the function returns a
non-zero value, the packet is processed; otherwise, it is
discarded. Default value: \fInids_ip_filter\fR (which always returns
1)
.TP
.I pcap_filter
pcap(3) filter string applied to the link-layer (raw, unassembled)
packets. \fBNote\fR: filters like ``tcp dst port 23'' will NOT
correctly handle appropriately fragmented traffic, e.g. 8-byte IP
fragments. Default value: NULL
.TP
.I promisc
If non-zero, libnids will set the interface(s) it listens on to
promiscuous mode. Default value: 1
.TP
.I one_loop_less
disabled by default; see comments in API.html file
.PP
Returns 1 on success, 0 on failure (in which case \fBnids_errbuf\fR
contains an appropriate error message).
.PP
.BR nids_register_ip_frag ()
registers a user-defined callback function to process all incoming IP
packets (including IP fragments, packets with invalid checksums, etc.).
.PP
.BR nids_register_ip ()
registers a user-defined callback function to process IP packets
validated and reassembled by \fBlibnids\fR.
.PP
.BR nids_register_udp ()
registers a user-defined callback function to process UDP packets
validated and reassembled by \fBlibnids\fR.
.PP
.BR nids_register_tcp ()
registers a user-defined callback function to process TCP streams
validated and reassembled by \fBlibnids\fR. The \fItcp_stream\fR
structure is defined as follows:
.LP
.nf
struct tcp_stream {
struct tuple4 {
u_short source;
u_short dest;
u_int saddr;
u_int daddr;
} addr;
char nids_state;
struct half_stream {
char state;
char collect;
char collect_urg;
char *data;
u_char urgdata;
int count;
int offset;
int count_new;
char count_new_urg;
...
} client;
struct half_stream server;
...
};
.fi
.PP
The members of the \fItuple4\fR structure identify a unique TCP
connection:
.TP
\fIsource\fR, \fIdest\fR
Client and server port numbers
.TP
\fIsaddr\fR, \fIdaddr\fR
Client and server IP addresses
.PP
The members of the \fIhalf_stream\fR structure describe each half of a
TCP connection (client and server):
.TP
.I state
Socket state (e.g. TCP_ESTABLISHED).
.TP
.I collect
A boolean which specifies whether to collect data for this half of the
connection in the \fIdata\fR buffer.
.TP
.I collect_urg
A boolean which specifies whether to collect urgent data pointed to by
the TCP urgent pointer for this half of the connection in the
\fIurgdata\fR buffer.
.TP
.I data
Buffer for normal data.
.TP
.I urgdata
One-byte buffer for urgent data.
.TP
.I count
The number of bytes appended to \fIdata\fR since the creation of the
connection.
.TP
.I offset
The current offset from the first byte stored in the \fIdata\fR
buffer, identifying the start of newly received data.
.TP
.I count_new
The number of bytes appended to \fIdata\fR since the last invocation
of the TCP callback function (if 0, no new data arrived).
.TP
.I count_new_urg
The number of bytes appended to \fIurgdata\fR since the last
invocation of the TCP callback function (if 0, no new urgent data
arrived).
.PP
The value of the \fInids_state\fR field provides information about the
state of the TCP connection, to be used by the TCP callback function:
.TP
NIDS_JUST_EST
Connection just established. Connection parameters in the \fIaddr\fR
structure are available for inspection. If the connection is
interesting, the TCP callback function may specify which data it
wishes to receive in the future by setting non-zero values for the
\fIcollect\fR or \fIcollect_urg\fR variables in the appropriate
\fIclient\fR or \fIserver\fR half_stream structure members.
.TP
NIDS_DATA
New data has arrived on a connection. The \fIhalf_stream\fR structures
contain buffers of data.
.TP
NIDS_CLOSE, NIDS_RESET, NIDS_TIMEOUT
Connection has closed. The TCP callback function should free any
resources it may have allocated for this connection.
.PP
The \fIparam\fR pointer may be set to save a pointer to user-defined
connection-specific data to pass to subsequent invocations of the TCP
callback function (ex. the current working directory for an FTP
control connection, etc.).
.PP
.BR nids_killtcp ()
tears down the specified TCP connection with symmetric RST packets
between client and server.
.PP
.BR nids_discard ()
may be called from the TCP callback function to specify the number of
bytes to discard from the beginning of the \fIdata\fR buffer (updating
the \fIoffset\fR value accordingly) after the TCP callback function
exits. Otherwise, the new data (totalling \fIcount_new\fR bytes) will
be discarded by default.
.PP
.BR nids_run ()
starts the packet-driven application, reading packets in an endless
loop, and invoking registered callback functions to handle new data as
it arrives. This function does not return.
.PP
.BR nids_next ()
sleeps until a packet arrives, and then processes a single packet
before returning. This allows the program to perform other tasks even
when no packets arrive. Returns 1 on success, 0 on failure (in which
case \fBnids_errbuf\fR contains an appropriate error message).
.PP
.BR nids_getfd ()
may be used by an application sleeping in select(2) to snoop for a
socket file descriptor present in the read fd_set. Returns the file
descriptor on success, -1 on failure (in which case \fBnids_errbuf\fR
contains an appropriate error message).
.SH SEE ALSO
pcap(3), libnet(3), fragrouter(8)
.SH AUTHOR
Rafal Wojtczuk
.PP
Manpage by Dug Song