S6-ACCESSRULES(7)

📦 version 2.15.1.0, in nixpkgs unstable

✨ s6-accessrules(7) ✨

okay so bestie, welcome to the s6-accessrules page from section 7 of the manual — the one and only accessrules library interface 💅

🌸 NAME 🌸

s6-accessrules — the accessrules library interface 🎀

💖 DESCRIPTION 💖

The functions and structures below are declared in the s6/accessrules.h header, and they're implemented in libs6.a or libs6.so. Periodt. 🫶

🦋 General information 🦋

s6-accessrules is an access control library, no cap. It looks up a key in a user-specified database, then returns a code depending on whether the database allows access (and in that case, extra info can be returned too), denies access, or just... doesn't contain the key at all 🙈.

It's been designed so it's easy to extend to literally any database format and any key format — very main character energy, very flexible ✨.

💡 Check the s6/accessrules.h header for the exact definitions, bestie.

🎀 Data structures 🎀

An s6_accessrules_result_t is a scalar that can have these values: S6_ACCESSRULES_ERROR, S6_ACCESSRULES_DENY, S6_ACCESSRULES_ALLOW or S6_ACCESSRULES_NOTFOUND. That's the whole vibe check — four possible outcomes 🔥.

An s6_accessrules_params_t is a structure containing two strallocs[1], .env and .exec, used to return data contained in the database when a key has been allowed. How you interpret that data? Application-defined, so that's on you 💜.

⭐ Function types ⭐

🔍 Backend lookups

An s6_accessrules_backend_func_t is the type of a function that takes a single key, looks it up in a database, and returns the result. Namely:

s6_accessrules_result_t f (char const *key, size_t keylen, void *handle, s6_accessrules_params_t *params)

f() looks up key key of length keylen in the database represented by handle, in an implementation-defined way. It returns a number that says the key has been allowed, denied or not found, or that an error occurred. If the key has been allowed, f stores additional information from the database into *params 💾.

Two s6_accessrules_backend_func_t functions are natively implemented:

  • s6_accessrules_backend_fs() — takes a char const * handle and interprets it as a base directory to look up key under, in the format understood by s6-accessrules-cdb-from-fs(8).
  • s6_accessrules_backend_cdb() — takes a struct cdb * handle and looks up key in the CDB[2] it points to. handle must already be mapped to a CDB file. Such a file can be built with the s6-accessrules-cdb-from-fs(8) utility.

🗝️ Frontend key checking

An s6_accessrules_keycheck_func_t is the type of a function that takes a user-level key, makes a list of corresponding backend-level keys, and calls an s6_accessrules_backend_func_t function until it finds a match. Namely:

s6_accessrules_result_t f (void const *key, void *handle, s6_accessrules_params_t *params, s6_accessrules_backend_func_t *backend)

f() derives a list of low-level keys to check from key. Then, for each key k of length klen in this list, it calls (*backend)(k, klen, handle, params), returning *backend's result if it is not S6_ACCESSRULES_NOTFOUND. If no match can be found in the whole list, f() finally returns S6_ACCESSRULES_NOTFOUND 😭.

Five s6_accessrules_keycheck_func_t functions are natively implemented — and these ones are iconic, let me walk you through 👑

  • s6_accessrules_keycheck_uidgid() — interprets key as a pointer to a structure containing an uid u and a gid g. The following checks are performed, in this order (i.e. subsequent checks are not performed if a match is found):
    • If u is equal to the effective uid of the process, look for a uid/self match.
    • Look for a uid/u match.
    • If g is equal to the effective gid of the process, look for a gid/self match.
    • Look for a gid/g match.
    • Look for a uid/default match.
  • s6_accessrules_keycheck_reversedns() — interprets key as a string containing an FQDN. Then for each suffix k of key, starting with key itself and ending with key's TLD, it looks up reversedns/k. The final dot is excluded from k. If no match can be found, the function checks reversedns/@ and returns the result. For instance, if key is "foo.bar.com", the following strings are looked up, in this order:
    • reversedns/foo.bar.com
    • reversedns/bar.com
    • reversedns/com
    • reversedns/@
  • s6_accessrules_keycheck_ip4() — interprets key as 4 network-byte-order characters containing an IPv4 address. Then for each netmask mask from 32 to 0, it constructs the IPv4 network prefix addr corresponding to that address, and looks up ip4/addr_mask. For instance, if key is "\300\250\001\007", representing the 192.168.1.7 address, the following strings are looked up, in this order:
    • ip4/192.168.1.7_32
    • ip4/192.168.1.6_31
    • ip4/192.168.1.4_30
    • ip4/192.168.1.0_29
    • ip4/192.168.0.0_28
    • ip4/192.168.0.0_27

and so on, down to:

  • ip4/192.0.0.0_3
  • ip4/192.0.0.0_2
  • ip4/128.0.0.0_1
  • ip4/0.0.0.0_0
⚠️ Note that the ip4/0.0.0.0_0 string is a catch-all key that matches everything. Everything, bestie. 💀
  • s6_accessrules_keycheck_ip6() — interprets key as 16 network-byte-order characters containing an IPv6 address. Then for each netmask mask from 128 to 0, it constructs the IPv6 network prefix addr corresponding to that address, in canonical form, and looks up ip6/addr_mask. For instance, if key is "*\0\024P@\002\b\003\0\0\0\0\0\0\020\006", representing the 2a00:1450:4002:803::1006 address, the following strings are looked up, in this order:
    • ip6/2a00:1450:4002:803::1006_128
    • ip6/2a00:1450:4002:803::1006_127
    • ip6/2a00:1450:4002:803::1004_126
    • ip6/2a00:1450:4002:803::1000_125
    • ip6/2a00:1450:4002:803::1000_124
    • ip6/2a00:1450:4002:803::1000_123
    • ip6/2a00:1450:4002:803::1000_122
    • ip6/2a00:1450:4002:803::1000_121
    • ip6/2a00:1450:4002:803::1000_120
    • ip6/2a00:1450:4002:803::1000_119
    • ip6/2a00:1450:4002:803::1000_118
    • ip6/2a00:1450:4002:803::1000_117
    • ip6/2a00:1450:4002:803::1000_116
    • ip6/2a00:1450:4002:803::1000_115
    • ip6/2a00:1450:4002:803::1000_114
    • ip6/2a00:1450:4002:803::1000_113
    • ip6/2a00:1450:4002:803::_112
    • ip6/2a00:1450:4002:803::_111

and so on, down to:

  • ip6/2a00::_11
  • ip6/2800::_10
  • ip6/2800::_9
  • ip6/2000::_8
  • ip6/2000::_7
  • ip6/2000::_6
  • ip6/2000::_5
  • ip6/2000::_4
  • ip6/2000::_3
  • ip6/::_2
  • ip6/::_1
  • ip6/::_0
⚠️ And note that the ip6/::_0 string is a catch-all key that matches everything too. Same energy, different address family 💅
  • s6_accessrules_keycheck_ip46() — interprets key as a pointer to an ip46_t[3], and behaves either as s6_accessrules_keycheck_ip6() or s6_accessrules_keycheck_ip4(), depending on the type of address *key contains. Versatile queen 🌈

💅 Ready-to-use functions 💅

These functions are mostly macros; they're built by associating a frontend function with a backend function. Basically grab-and-go, we love convenience 🍓

  • s6_accessrules_result_t s6_accessrules_uidgid_cdb(uid_t u, gid_t g, struct cdb *c, s6_accessrules_params_t *params) — Checks the *c CDB database for an authorization for uid u and gid g. If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_uidgid_fs(uid_t u, gid_t g, char const *dir, s6_accessrules_params_t *params) — Checks the dir base directory for an authorization for uid u and gid g. If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_reversedns_cdb(char const *name, struct cdb *c, s6_accessrules_params_t *params) — Checks the *c CDB database for an authorization for the name FQDN. If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_reversedns_fs(char const *name, char const *dir, s6_accessrules_params_t *params) — Checks the dir base directory for an authorization for the name FQDN. If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_ip4_cdb(char const *ip4, struct cdb *c, s6_accessrules_params_t *params) — Checks the *c CDB database for an authorization for the ip4 IPv4 address (4 network byte order characters). If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_ip4_fs(char const *ip4, char const *dir, s6_accessrules_params_t *params) — Checks the dir base directory for an authorization for the ip4 IPv4 address (4 network byte order characters). If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_ip6_cdb(char const *ip6, struct cdb *c, s6_accessrules_params_t *params) — Checks the *c CDB database for an authorization for the ip6 IPv6 address (16 network byte order characters). If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_ip6_fs(char const *ip6, char const *dir, s6_accessrules_params_t *params) — Checks the dir base directory for an authorization for the ip6 IPv6 address (16 network byte order characters). If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_ip46_cdb(ip46_t *ip, struct cdb *c, s6_accessrules_params_t *params) — Checks the *c CDB database for an authorization for the ip IP address. If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.
  • s6_accessrules_result_t s6_accessrules_ip46_fs(ip46_t const *ip, char const *dir, s6_accessrules_params_t *params) — Checks the dir base directory for an authorization for the ip IP address. If the result is S6_ACCESSRULES_ALLOW, additional information may be stored into params.

🔥 SEE ALSO 🔥

[1] https://skarnet.org/software/skalibs/libstddjb/stralloc.html

[2] https://cr.yp.to/cdb.html

[3] https://skarnet.org/software/skalibs/libstddjb/ip46.html

This man page is ported from the authoritative documentation at: https://skarnet.org/software/s6/libs6/accessrules.html 🧚

👑 AUTHORS 👑

  • Laurent Bercot
  • Alexis <flexibeast@gmail.com> (man page port)

and that's the whole page bestie, no details skipped, we ate and left no crumbs 💅✨ — cute little sign-off from Debian, dated September 29, 2021, page S6-ACCESSRULES(7), mwah 🫶🎀

📦 where this page comes from