PF(4)

💖 PF(4) — packet filter 💖

Kernel Interfaces Manual · section 4 · she's that girl 🦋

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✨ NAME ✨

pf — the packet filter. that's it. that's her whole government name 💅

✨ SYNOPSIS ✨

device pf
options PF_DEFAULT_TO_DROP

✨ DESCRIPTION ✨

okay so bestie, here's the tea ☕ — packet filtering happens in the kernel. not userland, not your little userspace scripts, the kernel. and there's this pseudo-device, /dev/pf, that lets userland processes control how the packet filter behaves, through an ioctl(2) interface 🫶

the ioctl(2) commands you get are: enable and disable the filter, load rulesets, add and remove individual rules or state table entries, and retrieve statistics. and if you're like "bestie I'm not doing all that by hand" — correct, because the most commonly used functions are covered by pfctl(8) ✨

now, important: manipulations like loading a ruleset that involve more than a single ioctl(2) call require a so-called ticket. the ticket's whole job is to prevent multiple concurrent manipulations from happening at the same time. it's giving "one person in the dressing room at a time" energy 💀

fields of ioctl(2) parameter structures that refer to packet data (like addresses and ports) are generally expected in network byte-order. ngl, remember that one.

rules and address tables live in so-called anchors. so when the kernel is servicing an ioctl(2) request, if the anchor field of the argument structure is empty, the kernel will use the default anchor (i.e., the main ruleset) in operations. anchors are specified by name and may be nested, with components separated by / characters — similar to how file system hierarchies are laid out 🗂️. and the final component of the anchor path is the anchor under which operations will be performed. periodt.

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✨ SYSCTL VARIABLES AND LOADER TUNABLES ✨

the following loader(8) tunables are available, bestie:

• net.pf.states_hashsize — size of hash tables that store states. should be a power of 2. default value is 131072.
• net.pf.source_nodes_hashsize — size of the hash table that stores source nodes. should be a power of 2. default value is 32768.

read only sysctl(8) variables with matching names are provided to obtain current values at runtime 👑

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✨ KERNEL OPTIONS ✨

the following options in the kernel configuration file are related to pf operation:

• PF_DEFAULT_TO_DROP — change default policy to drop by default 🔥

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✨ IOCTL INTERFACE ✨

pf supports the following ioctl(2) commands, available through ⟨net/pfvar.h⟩:

• DIOCSTART — start the packet filter.
• DIOCSTOP — stop the packet filter.
• DIOCSTARTALTQ — start the ALTQ bandwidth control system (see altq(9)).
• DIOCSTOPALTQ — stop the ALTQ bandwidth control system.
• DIOCBEGINADDRS struct pfioc_pooladdr *pp

struct pfioc_pooladdr {
        u_int32_t               action;
        u_int32_t               ticket;
        u_int32_t               nr;
        u_int32_t               r_num;
        u_int8_t                r_action;
        u_int8_t                r_last;
        u_int8_t                af;
        char                    anchor[MAXPATHLEN];
        struct pf_pooladdr      addr;
};

clear the buffer address pool and get a ticket for subsequent DIOCADDADDR, DIOCADDRULE, and DIOCCHANGERULE calls. 💖

• DIOCADDADDR struct pfioc_pooladdr *pp

add the pool address addr to the buffer address pool, to be used in the following DIOCADDRULE or DIOCCHANGERULE call. all other members of the structure are ignored — so don't stress about them 🫶

• DIOCADDRULE struct pfioc_rule *pr

struct pfioc_rule {
        u_int32_t       action;
        u_int32_t       ticket;
        u_int32_t       pool_ticket;
        u_int32_t       nr;
        char            anchor[MAXPATHLEN];
        char            anchor_call[MAXPATHLEN];
        struct pf_rule  rule;
};

add rule at the end of the inactive ruleset. this call requires a ticket obtained through a preceding DIOCXBEGIN call, and a pool_ticket obtained through a DIOCBEGINADDRS call. DIOCADDADDR must also be called if any pool addresses are required. the optional anchor name indicates the anchor in which to append the rule. nr and action are ignored ✨

• DIOCADDALTQ struct pfioc_altq *pa

add an ALTQ discipline or queue.

struct pfioc_altq {
        u_int32_t       action;
        u_int32_t       ticket;
        u_int32_t       nr;
        struct pf_altq  altq;
};

• DIOCGETRULES struct pfioc_rule *pr

get a ticket for subsequent DIOCGETRULE calls, and the number nr of rules in the active ruleset.

• DIOCGETRULE struct pfioc_rule *pr

get a rule by its number nr, using the ticket obtained through a preceding DIOCGETRULES call. and if action is set to PF_GET_CLR_CNTR, the per-rule statistics on the requested rule are cleared 💅

• DIOCGETADDRS struct pfioc_pooladdr *pp

get a ticket for subsequent DIOCGETADDR calls, and the number nr of pool addresses in the rule specified with r_action, r_num, and anchor.

• DIOCGETADDR struct pfioc_pooladdr *pp

get the pool address addr by its number nr from the rule specified with r_action, r_num, and anchor, using the ticket obtained through a preceding DIOCGETADDRS call.

• DIOCGETALTQS struct pfioc_altq *pa

get a ticket for subsequent DIOCGETALTQ calls, and the number nr of queues in the active list.

• DIOCGETALTQ struct pfioc_altq *pa

get the queueing discipline altq by its number nr, using the ticket obtained through a preceding DIOCGETALTQS call.

• DIOCGETQSTATS struct pfioc_qstats *pq

get the statistics on a queue.

struct pfioc_qstats {
        u_int32_t        ticket;
        u_int32_t        nr;
        void            *buf;
        int              nbytes;
        u_int8_t         scheduler;
};

this call fills in a pointer to the buffer of statistics buf, of length nbytes, for the queue specified by nr.

• DIOCGETRULESETS struct pfioc_ruleset *pr

struct pfioc_ruleset {
        u_int32_t        nr;
        char             path[MAXPATHLEN];
        char             name[PF_ANCHOR_NAME_SIZE];
};

get the number nr of rulesets (i.e., anchors) directly attached to the anchor named by path, for use in subsequent DIOCGETRULESET calls. and listen — nested anchors, since they are not directly attached to the given anchor, will not be included 🙈. this ioctl returns EINVAL if the given anchor does not exist.

• DIOCGETRULESET struct pfioc_ruleset *pr

get a ruleset (i.e., an anchor) name by its number nr from the given anchor path — the maximum number of which can be obtained from a preceding DIOCGETRULESETS call. this ioctl returns EINVAL if the given anchor does not exist, or EBUSY if another process is concurrently updating a ruleset. busy busy busy 💀

• DIOCADDSTATE struct pfioc_state *ps

add a state entry.

struct pfioc_state {
        struct pfsync_state     state;
};

• DIOCGETSTATE struct pfioc_state *ps

extract the entry identified by the id and creatorid fields of the state structure, from the state table.

• DIOCKILLSTATES struct pfioc_state_kill *psk

remove matching entries from the state table. this ioctl returns the number of killed states in psk_killed 🔪

struct pfioc_state_kill {
        struct pf_state_cmp     psk_pfcmp;
        sa_family_t             psk_af;
        int                     psk_proto;
        struct pf_rule_addr     psk_src;
        struct pf_rule_addr     psk_dst;
        char                    psk_ifname[IFNAMSIZ];
        char                    psk_label[PF_RULE_LABEL_SIZE];
        u_int                   psk_killed;
};

• DIOCCLRSTATES struct pfioc_state_kill *psk

clear all states. it works like DIOCKILLSTATES, but it ignores the psk_af, psk_proto, psk_src, and psk_dst fields of the pfioc_state_kill structure. yes bestie, all of them. no cap 😭

• DIOCSETSTATUSIF struct pfioc_if *pi

specify the interface for which statistics are accumulated.

struct pfioc_if {
        char             ifname[IFNAMSIZ];
};

• DIOCGETSTATUS struct pf_status *s

get the internal packet filter statistics.

struct pf_status {
        u_int64_t       counters[PFRES_MAX];
        u_int64_t       lcounters[LCNT_MAX];
        u_int64_t       fcounters[FCNT_MAX];
        u_int64_t       scounters[SCNT_MAX];
        u_int64_t       pcounters[2][2][3];
        u_int64_t       bcounters[2][2];
        u_int32_t       running;
        u_int32_t       states;
        u_int32_t       src_nodes;
        u_int32_t       since;
        u_int32_t       debug;
        u_int32_t       hostid;
        char            ifname[IFNAMSIZ];
        u_int8_t        pf_chksum[MD5_DIGEST_LENGTH];
};

• DIOCCLRSTATUS — clear the internal packet filter statistics.
• DIOCNATLOOK struct pfioc_natlook *pnl

look up a state table entry by source and destination addresses and ports.

struct pfioc_natlook {
        struct pf_addr   saddr;
        struct pf_addr   daddr;
        struct pf_addr   rsaddr;
        struct pf_addr   rdaddr;
        u_int16_t        sport;
        u_int16_t        dport;
        u_int16_t        rsport;
        u_int16_t        rdport;
        sa_family_t      af;
        u_int8_t         proto;
        u_int8_t         direction;
};

• DIOCSETDEBUG u_int32_t *level

set the debug level.

enum    { PF_DEBUG_NONE, PF_DEBUG_URGENT, PF_DEBUG_MISC,
          PF_DEBUG_NOISY };

• DIOCGETSTATES struct pfioc_states *ps

get state table entries.

struct pfioc_states {
        int     ps_len;
        union {
                caddr_t          psu_buf;
                struct pf_state *psu_states;
        } ps_u;
#define ps_buf          ps_u.psu_buf
#define ps_states       ps_u.psu_states
};

If ps_len is non-zero on entry, as many states as possible that can fit into this size will be copied into the supplied buffer ps_states. On exit, ps_len is always set to the total size required to hold all state table entries (i.e., it is set to sizeof(struct pf_state) * nr). lowkey the kernel is like “bestie I gotchu, here’s how much room you actually need” 💅

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DIOCCHANGERULE struct pfioc_rule *pcr

Add or remove the rule in the ruleset specified by rule.action. The type of operation to be performed is indicated by action, which can be any of the following:

enum    { PF_CHANGE_NONE, PF_CHANGE_ADD_HEAD, PF_CHANGE_ADD_TAIL,
          PF_CHANGE_ADD_BEFORE, PF_CHANGE_ADD_AFTER,
          PF_CHANGE_REMOVE, PF_CHANGE_GET_TICKET };

ticket must be set to the value obtained with PF_CHANGE_GET_TICKET for all actions except PF_CHANGE_GET_TICKET. pool_ticket must be set to the value obtained with the DIOCBEGINADDRS call for all actions except PF_CHANGE_REMOVE and PF_CHANGE_GET_TICKET. anchor indicates to which anchor the operation applies. nr indicates the rule number against which PF_CHANGE_ADD_BEFORE, PF_CHANGE_ADD_AFTER, or PF_CHANGE_REMOVE actions are applied. periodt, no cap. ✨

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DIOCCHANGEADDR struct pfioc_pooladdr *pca

Add or remove the pool address addr from the rule specified by r_action, r_num, and anchor. it’s giving “surgical rule editing” 💅

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DIOCSETTIMEOUT struct pfioc_tm *pt

struct pfioc_tm {
        int              timeout;
        int              seconds;
};

Set the state timeout of timeout to seconds. The old value will be placed into seconds. For possible values of timeout, consult the PFTM_* values in ⟨net/pfvar.h⟩. so you get a little trade: new value in, old value out. iconic. 🎀

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DIOCGETTIMEOUT struct pfioc_tm *pt

Get the state timeout of timeout. The value will be placed into the seconds field. just a lil peek, bestie. 👀

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DIOCCLRRULECTRS

Clear per-rule statistics. bye bye numbers, it’s a clean slate vibe. 🧼

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DIOCSETLIMIT struct pfioc_limit *pl

struct pfioc_limit {
        int             index;
        unsigned        limit;
};

enum    { PF_LIMIT_STATES, PF_LIMIT_SRC_NODES, PF_LIMIT_FRAGS,
          PF_LIMIT_TABLE_ENTRIES, PF_LIMIT_MAX };

Set the hard limits on the memory pools used by the packet filter. hard limits only, no soft launch energy here. 🔥

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DIOCGETLIMIT struct pfioc_limit *pl

Get the hard limit for the memory pool indicated by index. read the room, read the limit. 📖

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DIOCRCLRTABLES struct pfioc_table *io

Clear all tables. All the ioctls that manipulate radix tables use the same structure described below. For DIOCRCLRTABLES, pfrio_ndel contains on exit the number of tables deleted.

struct pfioc_table {
        struct pfr_table         pfrio_table;
        void                    *pfrio_buffer;
        int                      pfrio_esize;
        int                      pfrio_size;
        int                      pfrio_size2;
        int                      pfrio_nadd;
        int                      pfrio_ndel;
        int                      pfrio_nchange;
        int                      pfrio_flags;
        u_int32_t                pfrio_ticket;
};
#define pfrio_exists    pfrio_nadd
#define pfrio_nzero     pfrio_nadd
#define pfrio_nmatch    pfrio_nadd
#define pfrio_naddr     pfrio_size2
#define pfrio_setflag   pfrio_size2
#define pfrio_clrflag   pfrio_nadd

this struct is the main character for all the radix table ioctls, iykyk. 👑

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DIOCRADDTABLES struct pfioc_table *io

Create one or more tables. On entry, pfrio_buffer must point to an array of struct pfr_table containing at least pfrio_size elements. pfrio_esize must be the size of struct pfr_table. On exit, pfrio_nadd contains the number of tables effectively created.

struct pfr_table {
        char            pfrt_anchor[MAXPATHLEN];
        char            pfrt_name[PF_TABLE_NAME_SIZE];
        u_int32_t       pfrt_flags;
        u_int8_t        pfrt_fback;
};

table creation? slay. just don’t forget pfrio_esize or the vibe check fails. ✨

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DIOCRDELTABLES struct pfioc_table *io

Delete one or more tables. On entry, pfrio_buffer must point to an array of struct pfr_table containing at least pfrio_size elements. pfrio_esize must be the size of struct pfr_table. On exit, pfrio_ndel contains the number of tables effectively deleted. ghosting tables, but make it kernel-official. 💀

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DIOCRGETTABLES struct pfioc_table *io

Get the list of all tables. On entry, pfrio_buffer[pfrio_size] contains a valid writeable buffer for pfr_table structures. On exit, pfrio_size contains the number of tables written into the buffer. If the buffer is too small, the kernel does not store anything but just returns the required buffer size, without error. no error, just “bestie your buffer is too small, here’s the size you need.” 📏

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DIOCRGETTSTATS struct pfioc_table *io

This call is like DIOCRGETTABLES but is used to get an array of pfr_tstats structures.

struct pfr_tstats {
        struct pfr_table pfrts_t;
        u_int64_t        pfrts_packets
                             [PFR_DIR_MAX][PFR_OP_TABLE_MAX];
        u_int64_t        pfrts_bytes
                             [PFR_DIR_MAX][PFR_OP_TABLE_MAX];
        u_int64_t        pfrts_match;
        u_int64_t        pfrts_nomatch;
        long             pfrts_tzero;
        int              pfrts_cnt;
        int              pfrts_refcnt[PFR_REFCNT_MAX];
};
#define pfrts_name       pfrts_t.pfrt_name
#define pfrts_flags      pfrts_t.pfrt_flags

stats on stats on stats. the way that pfrts_packets and pfrts_bytes are 2D arrays? highkey iconic. 📊

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DIOCRCLRTSTATS struct pfioc_table *io

Clear the statistics of one or more tables. On entry, pfrio_buffer must point to an array of struct pfr_table containing at least pfrio_size elements. pfrio_esize must be the size of struct pfr_table. On exit, pfrio_nzero contains the number of tables effectively cleared. reset era. 🧼

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DIOCRCLRADDRS struct pfioc_table *io

Clear all addresses in a table. On entry, pfrio_table contains the table to clear. On exit, pfrio_ndel contains the number of addresses removed. address cleanup, but make it fashion. 🧹

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DIOCRADDADDRS struct pfioc_table *io

Add one or more addresses to a table. On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements to add to the table. pfrio_esize must be the size of struct pfr_addr. On exit, pfrio_nadd contains the number of addresses effectively added.

struct pfr_addr {
        union {
                struct in_addr   _pfra_ip4addr;
                struct in6_addr  _pfra_ip6addr;
        }                pfra_u;
        u_int8_t         pfra_af;
        u_int8_t         pfra_net;
        u_int8_t         pfra_not;
        u_int8_t         pfra_fback;
};
#define pfra_ip4addr    pfra_u._pfra_ip4addr
#define pfra_ip6addr    pfra_u._pfra_ip6addr

v4 or v6? the union said “why not both?” 💅

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DIOCRDELADDRS struct pfioc_table *io

Delete one or more addresses from a table. On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements to delete from the table. pfrio_esize must be the size of struct pfr_addr. On exit, pfrio_ndel contains the number of addresses effectively deleted. unsubscribing addresses from the table’s newsletter. 💀

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DIOCRSETADDRS struct pfioc_table *io

Replace the content of a table by a new address list. This is the most complicated command, which uses all the structure members.

On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements which become the new contents of the table. pfrio_esize must be the size of struct pfr_addr. Additionally, if pfrio_size2 is non-zero, pfrio_buffer[pfrio_size..pfrio_size2] must be a writeable buffer, into which the kernel can copy the addresses that have been deleted during the replace operation. On exit, pfrio_ndel, pfrio_nadd, and pfrio_nchange contain the number of addresses deleted, added, and changed by the kernel. If pfrio_size2 was set on entry, pfrio_size2 will point to the size of the buffer used, exactly like DIOCRGETADDRS.

this one is the final boss of table ioctls. all the structure members are in the group chat for this one. 🔥

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DIOCRGETADDRS struct pfioc_table *io

Get all the addresses of a table. On entry, pfrio_table contains the table ID and pfrio_buffer[pfrio_size] contains a valid writeable buffer for pfr_addr structures. On exit, pfrio_size contains the number of addresses written into the buffer. If the buffer was too small, the kernel does not store anything but just returns the required buffer size, without returning an error. same energy as DIOCRGETTABLES: no error, just the size you actually need. bestie behavior. 🫶

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DIOCRGETASTATS struct pfioc_table *io

This call is like DIOCRGETADDRS but is used to get an array of pfr_astats structures.

struct pfr_astats {
        struct pfr_addr  pfras_a;
        u_int64_t        pfras_packets
                             [PFR_DIR_MAX][PFR_OP_ADDR_MAX];
        u_int64_t        pfras_bytes
                             [PFR_DIR_MAX][PFR_OP_ADDR_MAX];
        long             pfras_tzero;
};

address stats, but make it structured. the way that pfras_packets and pfras_bytes are also 2D? obsessed. ✨

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DIOCRCLRASTATS struct pfioc_table *io

Clear the statistics of one or more addresses. On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements to be cleared from the table. pfrio_esize must be the size of struct pfr_addr. On exit, pfrio_nzero contains the number of addresses effectively cleared. stats? cleared. periodt. 🧼

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DIOCRTSTADDRS struct pfioc_table *io

Test if the given addresses match a table. On entry, pfrio_table contains the table ID and pfrio_buffer must point to an array of struct pfr_addr containing at least pfrio_size elements, each of which will be tested for a match in the table. pfrio_esize must be the size of struct pfr_addr. On exit, the kernel updates the pfr_addr array by setting the pfra_fback member appropriately. vibe check for addresses. the kernel sets pfra_fback and that’s the tea. 🍵

💅 DIOCRSETTFLAGS

struct pfioc_table *io — okay bestie, this one is giving flag-editing energy. It changes the PFR_TFLAG_CONST or PFR_TFLAG_PERSIST flags of a table. On entry, pfrio_buffer must point to an array of struct pfr_table containing at least pfrio_size elements. pfrio_esize must be the size of struct pfr_table. pfrio_setflag must contain the flags to add, while pfrio_clrflag must contain the flags to remove. On exit, pfrio_nchange and pfrio_ndel contain the number of tables altered or deleted by the kernel. Yes, tables can be deleted if one removes the PFR_TFLAG_PERSIST flag of an unreferenced table. 💖

🌸 DIOCRINADEFINE

struct pfioc_table *io — this defines a table in the inactive set. On entry, pfrio_table contains the table ID and pfrio_buffer[pfrio_size] contains an array of pfr_addr structures to put in the table. A valid ticket must also be supplied to pfrio_ticket. On exit, pfrio_nadd contains 0 if the table was already defined in the inactive list or 1 if a new table has been created. pfrio_naddr contains the number of addresses effectively put in the table. Slay. ✨

🦋 DIOCXBEGIN

struct pfioc_trans *io

struct pfioc_trans {
        int              size;  /* number of elements */
        int              esize; /* size of each element in bytes */
        struct pfioc_trans_e {
                int             rs_num;
                char            anchor[MAXPATHLEN];
                u_int32_t       ticket;
        }               *array;
};

Clear all the inactive rulesets specified in the pfioc_trans_e array. For each ruleset, a ticket is returned for subsequent "add rule" ioctls, as well as for the DIOCXCOMMIT and DIOCXROLLBACK calls.

Ruleset types, identified by rs_num, include the following:

• PF_RULESET_SCRUB — Scrub (packet normalization) rules.
• PF_RULESET_FILTER — Filter rules.
• PF_RULESET_NAT — NAT (Network Address Translation) rules.
• PF_RULESET_BINAT — Bidirectional NAT rules.
• PF_RULESET_RDR — Redirect rules.
• PF_RULESET_ALTQ — ALTQ disciplines.
• PF_RULESET_TABLE — Address tables.

👑 DIOCXCOMMIT

struct pfioc_trans *io — atomically switch a vector of inactive rulesets to the active rulesets. This call is implemented as a standard two-phase commit, which will either fail for all rulesets or completely succeed. All tickets need to be valid. This ioctl returns EBUSY if another process is concurrently updating some of the same rulesets. 💀

🧚 DIOCXROLLBACK

struct pfioc_trans *io — cleans up the kernel by undoing all changes that have taken place on the inactive rulesets since the last DIOCXBEGIN. DIOCXROLLBACK will silently ignore rulesets for which the ticket is invalid. No drama, just rollback. 🙈

🌈 DIOCSETHOSTID

u_int32_t *hostid — sets the host ID, which is used by pfsync(4) to identify which host created state table entries. 🫶

🍓 DIOCOSFPFLUSH

Flushes the passive OS fingerprint table. Gone. Deleted. Periodt. 💅

⭐ DIOCOSFPADD

struct pf_osfp_ioctl *io

struct pf_osfp_ioctl {
        struct pf_osfp_entry {
                SLIST_ENTRY(pf_osfp_entry) fp_entry;
                pf_osfp_t               fp_os;
                char                    fp_class_nm[PF_OSFP_LEN];
                char                    fp_version_nm[PF_OSFP_LEN];
                char                    fp_subtype_nm[PF_OSFP_LEN];
        }                       fp_os;
        pf_tcpopts_t            fp_tcpopts;
        u_int16_t               fp_wsize;
        u_int16_t               fp_psize;
        u_int16_t               fp_mss;
        u_int16_t               fp_flags;
        u_int8_t                fp_optcnt;
        u_int8_t                fp_wscale;
        u_int8_t                fp_ttl;
        int                     fp_getnum;
};

Add a passive OS fingerprint to the table. Set fp_os.fp_os to the packed fingerprint, fp_os.fp_class_nm to the name of the class (Linux, Windows, etc), fp_os.fp_version_nm to the name of the version (NT, 95, 98), and fp_os.fp_subtype_nm to the name of the subtype or patchlevel. The members fp_mss, fp_wsize, fp_psize, fp_ttl, fp_optcnt, and fp_wscale are set to the TCP MSS, the TCP window size, the IP length, the IP TTL, the number of TCP options, and the TCP window scaling constant of the TCP SYN packet, respectively.

The fp_flags member is filled according to the ⟨net/pfvar.h⟩ include file PF_OSFP_* defines. The fp_tcpopts member contains packed TCP options. Each option uses PF_OSFP_TCPOPT_BITS bits in the packed value. Options include any of PF_OSFP_TCPOPT_NOP, PF_OSFP_TCPOPT_SACK, PF_OSFP_TCPOPT_WSCALE, PF_OSFP_TCPOPT_MSS, or PF_OSFP_TCPOPT_TS.

The fp_getnum member is not used with this ioctl.

The structure's slack space must be zeroed for correct operation; memset(3) the whole structure to zero before filling and sending to the kernel. No cap, bestie — zero it or risk the vibe check failing. 💖

💜 DIOCOSFPGET

struct pf_osfp_ioctl *io — get the passive OS fingerprint number fp_getnum from the kernel's fingerprint list. The rest of the structure members will come back filled. Get the whole list by repeatedly incrementing the fp_getnum number until the ioctl returns EBUSY. Keep going until it says stop. 🔥

🌸 DIOCGETSRCNODES

struct pfioc_src_nodes *psn

struct pfioc_src_nodes {
        int     psn_len;
        union {
                caddr_t         psu_buf;
                struct pf_src_node      *psu_src_nodes;
        } psn_u;
#define psn_buf         psn_u.psu_buf
#define psn_src_nodes   psn_u.psu_src_nodes
};

Get the list of source nodes kept by sticky addresses and source tracking. The ioctl must be called once with psn_len set to 0. If the ioctl returns without error, psn_len will be set to the size of the buffer required to hold all the pf_src_node structures held in the table. A buffer of this size should then be allocated, and a pointer to this buffer placed in psn_buf. The ioctl must then be called again to fill this buffer with the actual source node data. After that call, psn_len will be set to the length of the buffer actually used. Two-step process, but it ate. ✨

🎀 DIOCCLRSRCNODES

Clear the tree of source tracking nodes. Done and dusted. 💅

🦋 DIOCIGETIFACES

struct pfioc_iface *io — get the list of interfaces and interface drivers known to pf. All the ioctls that manipulate interfaces use the same structure described below:

struct pfioc_iface {
        char                     pfiio_name[IFNAMSIZ];
        void                    *pfiio_buffer;
        int                      pfiio_esize;
        int                      pfiio_size;
        int                      pfiio_nzero;
        int                      pfiio_flags;
};

If not empty, pfiio_name can be used to restrict the search to a specific interface or driver. pfiio_buffer[pfiio_size] is the user-supplied buffer for returning the data. On entry, pfiio_size contains the number of pfi_kif entries that can fit into the buffer. The kernel will replace this value by the real number of entries it wants to return. pfiio_esize should be set to sizeof(struct pfi_kif).

The data is returned in the pfi_kif structure described below:

struct pfi_kif {
        RB_ENTRY(pfi_kif)                pfik_tree;
        char                             pfik_name[IFNAMSIZ];
        u_int64_t                        pfik_packets[2][2][2];
        u_int64_t                        pfik_bytes[2][2][2];
        u_int32_t                        pfik_tzero;
        int                              pfik_flags;
        struct pf_state_tree_lan_ext     pfik_lan_ext;
        struct pf_state_tree_ext_gwy     pfik_ext_gwy;
        TAILQ_ENTRY(pfi_kif)             pfik_w_states;
        void                            *pfik_ah_cookie;
        struct ifnet                    *pfik_ifp;
        struct ifg_group                *pfik_group;
        int                              pfik_states;
        int                              pfik_rules;
        TAILQ_HEAD(, pfi_dynaddr)        pfik_dynaddrs;
};

💖 DIOCSETIFFLAG

struct pfioc_iface *io — set the user settable flags (described above) of the pf internal interface description. The filtering process is the same as for DIOCIGETIFACES.

#define PFI_IFLAG_SKIP  0x0100  /* skip filtering on interface */

🌈 DIOCCLRIFFLAG

struct pfioc_iface *io — works as DIOCSETIFFLAG above but clears the flags. Reverse uno card. 🫶

🔥 DIOCKILLSRCNODES

struct pfioc_iface *io — explicitly remove source tracking nodes. Periodt.

---

📁 FILES 📁

• /dev/pf — packet filtering device. 👑

✨ EXAMPLES ✨

okay bestie this is the moment you've been waiting for 💖 here's a whole literal program showing you how to use the DIOCNATLOOK command to find the internal host/port of a NATed connection. it's giving "finally, something i can copy-paste". no cap.

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/fcntl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <net/pfvar.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>

u_int32_t
read_address(const char *s)
{
        int a, b, c, d;

        sscanf(s, "%i.%i.%i.%i", &a, &b, &c, &d);
        return htonl(a << 24 | b << 16 | c << 8 | d);
}

void
print_address(u_int32_t a)
{
        a = ntohl(a);
        printf("%d.%d.%d.%d", a >> 24 & 255, a >> 16 & 255,
            a >> 8 & 255, a & 255);
}

int
main(int argc, char *argv[])
{
        struct pfioc_natlook nl;
        int dev;

        if (argc != 5) {
                printf("%s <gwy addr> <gwy port> <ext addr> <ext port>\n",
                    argv[0]);
                return 1;
        }

        dev = open("/dev/pf", O_RDWR);
        if (dev == -1)
                err(1, "open(\"/dev/pf\") failed");

        memset(&nl, 0, sizeof(struct pfioc_natlook));
        nl.saddr.v4.s_addr      = read_address(argv[1]);
        nl.sport                = htons(atoi(argv[2]));
        nl.daddr.v4.s_addr      = read_address(argv[3]);
        nl.dport                = htons(atoi(argv[4]));
        nl.af                   = AF_INET;
        nl.proto                = IPPROTO_TCP;
        nl.direction            = PF_IN;

        if (ioctl(dev, DIOCNATLOOK, &nl))
                err(1, "DIOCNATLOOK");

        printf("internal host ");
        print_address(nl.rsaddr.v4.s_addr);
        printf(":%u\n", ntohs(nl.rsport));
        return 0;
}

the way this little guy opens /dev/pf with O_RDWR, zeroes out the whole struct pfioc_natlook, fills in the source and destination, sets nl.af to AF_INET, nl.proto to IPPROTO_TCP and nl.direction to PF_IN — and then asks the kernel "bestie who is this really" via DIOCNATLOOK and prints the internal host and port it gets back 🫶 iconic behaviour honestly 💅

---

🌸 SEE ALSO 🌸

• ioctl(2)
• altq(4)
• if_bridge(4)
• pflog(4)
• pfsync(4)
• pfctl(8)
• altq(9)

go read those too, i'm literally begging 🙈 they're the supporting cast and they ate ✨

---

👑 HISTORY 👑

okay storytime, gather round 🎀

• the pf packet filtering mechanism first appeared in OpenBSD 3.0 and then FreeBSD 5.2. a true main character debut moment ⭐
• this implementation is derived from OpenBSD 4.5. it has been heavily modified so it can run in a multithreaded FreeBSD kernel and scale its performance on multiple CPUs. glow up of the century fr fr 🔥

ngl the multithreading + multi-CPU scaling rewrite is the real flex here. it's giving "i didn't come to play, i came to perform" 💀💖

---

and that's the whole page bestie!! 🦋 you made it to the end, i'm so proud of you 😭💖

this beauty comes from Debian, dated August 5, 2018, and it lives in section PF(4) of your manual pages 💅

slay, go filter some packets responsibly, and remember: every single flag matters 👑✨🌸🎀💜