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NAME

ipf − packet filtering kernel interface

SYNOPSIS

#include <netinet/ip_compat.h>
#include <netinet/ip_fil.h>

IOCTLS

To add and delete rules to the filter list, three ’basic’ ioctls are provided for use. The ioctl’s are called as:

However, the full complement is as follows:

The variations, SIOCADAFR vs. SIOCADIFR, allow operation on the two lists, active and inactive, respectively. All of these ioctl’s are implemented as being routing ioctls and thus the same rules for the various routing ioctls and the file descriptor are employed, mainly being that the fd must be that of the device associated with the module (i.e., /dev/ipl).

The three groups of ioctls above perform adding rules to the end of the list (SIOCAD*), deletion of rules from any place in the list (SIOCRM*) and insertion of a rule into the list (SIOCIN*). The rule place into which it is inserted is stored in the "fr_hits" field, below.

typedef struct frentry {
struct frentry *fr_next;
u_short fr_group; /* group to which this rule belongs */
u_short fr_grhead; /* group # which this rule starts */
struct frentry *fr_grp;
int fr_ref; /* reference count - for grouping */
void *fr_ifa;
#if BSD >= 199306
void *fr_oifa;
#endif
/*
* These are only incremented when a packet matches this rule and
* it is the last match
*/
U_QUAD_T fr_hits;
U_QUAD_T fr_bytes;
/*
* Fields after this may not change whilst in the kernel.
*/
struct fr_ip fr_ip;
struct fr_ip fr_mip; /* mask structure */

u_char fr_tcpfm; /* tcp flags mask */
u_char fr_tcpf; /* tcp flags */

u_short fr_icmpm; /* data for ICMP packets (mask) */
u_short fr_icmp;

u_char fr_scmp; /* data for port comparisons */
u_char fr_dcmp;
u_short fr_dport;
u_short fr_sport;
u_short fr_stop; /* top port for <> and >< */
u_short fr_dtop; /* top port for <> and >< */
u_32_t fr_flags; /* per-rule flags && options (see below) */
u_short fr_skip; /* # of rules to skip */
u_short fr_loglevel; /* syslog log facility + priority */
int (*fr_func) __P((int, ip_t *, fr_info_t *));
char fr_icode; /* return ICMP code */
char fr_ifname[IFNAMSIZ];
#if BSD > 199306
char fr_oifname[IFNAMSIZ];
#endif
struct frdest fr_tif; /* "to" interface */
struct frdest fr_dif; /* duplicate packet interfaces */
} frentry_t;

When adding a new rule, all unused fields (in the filter rule) should be initialised to be zero. To insert a rule, at a particular position in the filter list, the number of the rule which it is to be inserted before must be put in the "fr_hits" field (the first rule is number 0).

Flags which are recognised in fr_flags:

FR_BLOCK 0x000001 /* do not allow packet to pass */
FR_PASS 0x000002 /* allow packet to pass */
FR_OUTQUE 0x000004 /* outgoing packets */
FR_INQUE 0x000008 /* ingoing packets */
FR_LOG 0x000010 /* Log */
FR_LOGB 0x000011 /* Log-fail */
FR_LOGP 0x000012 /* Log-pass */
FR_LOGBODY 0x000020 /* log the body of packets too */
FR_LOGFIRST 0x000040 /* log only the first packet to match */
FR_RETRST 0x000080 /* return a TCP RST packet if blocked */
FR_RETICMP 0x000100 /* return an ICMP packet if blocked */
FR_FAKEICMP 0x00180 /* Return ICMP unreachable with fake source */
FR_NOMATCH 0x000200 /* no match occured */
FR_ACCOUNT 0x000400 /* count packet bytes */
FR_KEEPFRAG 0x000800 /* keep fragment information */
FR_KEEPSTATE 0x001000 /* keep ’connection’ state information */
FR_INACTIVE 0x002000
FR_QUICK 0x004000 /* match & stop processing list */
FR_FASTROUTE 0x008000 /* bypass normal routing */
FR_CALLNOW 0x010000 /* call another function (fr_func) if matches */
FR_DUP 0x020000 /* duplicate the packet */
FR_LOGORBLOCK 0x040000 /* block the packet if it can’t be logged */
FR_NOTSRCIP 0x080000 /* not the src IP# */
FR_NOTDSTIP 0x100000 /* not the dst IP# */
FR_AUTH 0x200000 /* use authentication */
FR_PREAUTH 0x400000 /* require preauthentication */

Values for fr_scomp and fr_dcomp (source and destination port value comparisons) :

The third ioctl, SIOCIPFFL, flushes either the input filter list, the output filter list or both and it returns the number of filters removed from the list(s). The values which it will take and recognise are FR_INQUE and FR_OUTQUE (see above). This ioctl is also implemented for /dev/ipstate and will flush all state tables entries if passed 0 or just all those which are not established if passed 1.
General Logging Flags
There are two flags which can be set to log packets independently of the rules used. These allow for packets which are either passed or blocked to be logged. To set (and clear)/get these flags, two ioctls are provided:

FF_LOGPASS 0x10000000

Filter statistics
Statistics on the various operations performed by this package on packets is kept inside the kernel. These statistics apply to packets traversing through the kernel. To retrieve this structure, use this ioctl:

ioctl(fd, SIOCGETFS, struct friostat *)

struct friostat {
struct filterstats f_st[2];
struct frentry *f_fin[2];
struct frentry *f_fout[2];
struct frentry *f_acctin[2];
struct frentry *f_acctout[2];
struct frentry *f_auth;
u_long f_froute[2];
int f_active; /* 1 or 0 - active rule set */
int f_defpass; /* default pass - from fr_pass */
int f_running; /* 1 if running, else 0 */
int f_logging; /* 1 if enabled, else 0 */
char f_version[32]; /* version string */
};

u_long fr_pass; /* packets allowed */
u_long fr_block; /* packets denied */
u_long fr_nom; /* packets which don’t match any rule */
u_long fr_ppkl; /* packets allowed and logged */
u_long fr_bpkl; /* packets denied and logged */
u_long fr_npkl; /* packets unmatched and logged */
u_long fr_pkl; /* packets logged */
u_long fr_skip; /* packets to be logged but buffer full */
u_long fr_ret; /* packets for which a return is sent */
u_long fr_acct; /* packets for which counting was performed */
u_long fr_bnfr; /* bad attempts to allocate fragment state */
u_long fr_nfr; /* new fragment state kept */
u_long fr_cfr; /* add new fragment state but complete pkt */
u_long fr_bads; /* bad attempts to allocate packet state */
u_long fr_ads; /* new packet state kept */
u_long fr_chit; /* cached hit */
u_long fr_pull[2]; /* good and bad pullup attempts */
#if SOLARIS
u_long fr_notdata; /* PROTO/PCPROTO that have no data */
u_long fr_nodata; /* mblks that have no data */
u_long fr_bad; /* bad IP packets to the filter */
u_long fr_notip; /* packets passed through no on ip queue */
u_long fr_drop; /* packets dropped - no info for them! */
#endif
};
If we wanted to retrieve all the statistics and reset the counters back to 0, then the ioctl() call would be made to SIOCFRZST rather than SIOCGETFS. In addition to the statistics above, each rule keeps a hit count, counting both number of packets and bytes. To reset these counters for a rule, load the various rule information into a frentry structure and call SIOCZRLST.
Swapping Active lists
IP Filter supports two lists of rules for filtering and accounting: an active list and an inactive list. This allows for large scale rule base changes to be put in place atomically with otherwise minimal interruption. Which of the two is active can be changed using the SIOCSWAPA ioctl. It is important to note that no passed argument is recognised and that the value returned is that of the list which is now inactive.

FILES

/dev/ipauth
/dev/ipl
/dev/ipnat
/dev/ipstate

SEE ALSO

ipl(4), ipnat(4), ipf(5), ipf(8), ipfstat(8)