s6-accessrules.7

.Dd September 29, 2021
.Dt S6-ACCESSRULES 7
.Os
.Sh NAME
.Nm s6-accessrules
.Nd the accessrules library interface
.Sh DESCRIPTION
The following functions and structures are declared in the
.Pa s6/accessrules.h
header, and implemented in
.Pa libs6.a
or
.Pa libs6.so .
.Ss General information
.Nm
is an access control library.
It looks up a key in a user-specified database, then returns a code
depending on whether the database allows access (in which case
additional information can also be returned), denies access, or does
not contain the key.
.Pp
.Nm
has been designed to be easily extensible to any database format and
any key format.
.Pp
Check the
.Pa s6/accessrules.h
header for the exact definitions.
.Ss Data structures
An
.Vt s6_accessrules_result_t
is a scalar that can have the following values:
.Dv S6_ACCESSRULES_ERROR ,
.Dv S6_ACCESSRULES_DENY ,
.Dv S6_ACCESSRULES_ALLOW
or
.Dv S6_ACCESSRULES_NOTFOUND .
.Pp
An
.Vt s6_accessrules_params_t
is a structure containing two strallocs[1],
.Em .env
and
.Em .exec ,
used to return data contained in the database when a key has been
allowed.
The interpretation of this data is application-defined.
.Ss Function types
.Sy Backend lookups
.Pp
An
.Ft 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:
.Pp
.Dl s6_accessrules_result_t f (char const *key, size_t keylen, void *handle, s6_accessrules_params_t *params)
.Pp
.Fn f
looks up key
.Va key
of length
.Va keylen
in the database represented by
.Va handle
in an implementation-defined way.
It returns a number that says the key has been allowed, denied or not
found, or an error occurred.
If the key has been allowed,
.Va f
stores additional information from the database into
.Va *params .
.Pp
Two
.Ft s6_accessrules_backend_func_t
functions are natively implemented:
.Bl -bullet -width x
.It
.Fn s6_accessrules_backend_fs
takes a
.Vt char const *
.Va handle
and interprets it as a base directory to look up
.Va key
under, in the format understood by
.Xr s6-accessrules-cdb-from-fs 8 .
.It
.Fn s6_accessrules_backend_cdb
takes a
.Vt struct cdb *
.Va handle
and looks up
.Va key
in the CDB[2] it points to.
.Va handle
must already be mapped to a CDB file.
Such a file can be built with the
.Xr s6-accessrules-cdb-from-fs 8
utility.
.El
.Pp
.Sy Frontend key checking
.Pp
An
.Ft 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 a
.Ft s6_accessrules_backend_func_t
function until it finds a match.
Namely:
.Pp
.Dl s6_accessrules_result_t f (void const *key, void *handle, s6_accessrules_params_t *params, s6_accessrules_backend_func_t *backend)
.Pp
.Fn f
derives a list of low-level keys to check from
.Va key .
Then, for each key
.Va k
of length
.Va klen
in this list, it calls
.Ql (*backend)(k, klen, handle, params) ,
returning
.Va *backend Ap
s result if it is not
.Dv S6_ACCESSRULES_NOTFOUND .
If no match can be found in the whole list,
.Fn f
finally returns
.Dv S6_ACCESSRULES_NOTFOUND .
.Pp
Five
.Ft s6_accessrules_keycheck_func_t
functions are natively implemented:
.Bl -bullet -width x
.It
.Fn s6_accessrules_keycheck_uidgid
interprets
.Va key
as a pointer to a structure containing an uid
.Va u
and a gid
.Va g .
The following checks are performed, in this order (i.e. subsequent
checks are not performed if a match is found):
.Bl -bullet -width x
.It
If
.Va u
is equal to the effective uid of the process, look for a
.Pa uid/self
match.
.It
Look for a
.Sm off
.Pa uid/
.Va u
.Sm on
match.
.It
If
.Va g
is equal to the effective gid of the process, look for a
.Pa gid/self
match.
.It
Look for a
.Sm off
.Pa gid/
.Va g
.Sm on
match.
.It
Look for a
.Pa uid/default
match.
.El
.It
.Fn s6_accessrules_keycheck_reversedns
interprets
.Va key
as a string containing an FQDN.
Then for each suffix
.Va k
of
.Va key ,
starting with
.Va key
itself and ending with
.Va key Ap
s TLD, it looks up
.Sm off
.Pa reversedns/
.Va k
.Sm on .
The final dot is excluded from
.Va k .
If no match can be found, the function checks
.Pa reversedns/@
and returns the result.
For instance, if
.Va key
is
.Dq foo.bar.com ,
the following strings are looked up, in this order:
.Bl -bullet -width x
.It
reversedns/foo.bar.com
.It
reversedns/bar.com
.It
reversedns/com
.It
reversedns/@
.El
.It
.Fn s6_accessrules_keycheck_ip4
interprets
.Va key
as 4 network-byte-order characters containing an IPv4 address.
Then for each netmask
.Va mask
from 32 to 0, it constructs the IPv4 network prefix
.Va addr
corresponding to that address, and looks up
.Sm off
.Pa ip4/
.Va addr Ns _ Ns Va mask
.Sm on .
For instance, if
.Va key
is
.Dq \e300\e250\e001\e007 ,
representing the 192.168.1.7 address, the following strings are looked
up, in this order:
.Bl -bullet -width x
.It
ip4/192.168.1.7_32
.It
ip4/192.168.1.6_31
.It
ip4/192.168.1.4_30
.It
ip4/192.168.1.0_29
.It
ip4/192.168.0.0_28
.It
ip4/192.168.0.0_27
.El
.Pp
and so on, down to:
.Bl -bullet -width x
.It
ip4/192.0.0.0_3
.It
ip4/192.0.0.0_2
.It
ip4/128.0.0.0_1
.It
ip4/0.0.0.0_0
.El
.Pp
Note that the
.Ql ip4/0.0.0.0_0
string is a catch-all key that matches everything.
.It
.Fn s6_accessrules_keycheck_ip6
interprets
.Va key
as 16 network-byte-order characters containing an IPv6 address.
Then for each netmask
.Va mask
from 128 to 0, it constructs the IPv6 network prefix
.Va addr
corresponding to that address, in canonical form, and looks up
.Sm off
.Pa ip6/
.Va addr Ns _ Ns Va mask
.Sm on .
For instance, if
.Va key
is
.Dq *\e0\e024P@\e002\eb\e003\e0\e0\e0\e0\e0\e0\e020\e006 ,
representing the 2a00:1450:4002:803::1006 address, the following
strings are looked up, in this order:
.Bl -bullet -width x
.It
ip6/2a00:1450:4002:803::1006_128
.It
ip6/2a00:1450:4002:803::1006_127
.It
ip6/2a00:1450:4002:803::1004_126
.It
ip6/2a00:1450:4002:803::1000_125
.It
ip6/2a00:1450:4002:803::1000_124
.It
ip6/2a00:1450:4002:803::1000_123
.It
ip6/2a00:1450:4002:803::1000_122
.It
ip6/2a00:1450:4002:803::1000_121
.It
ip6/2a00:1450:4002:803::1000_120
.It
ip6/2a00:1450:4002:803::1000_119
.It
ip6/2a00:1450:4002:803::1000_118
.It
ip6/2a00:1450:4002:803::1000_117
.It
ip6/2a00:1450:4002:803::1000_116
.It
ip6/2a00:1450:4002:803::1000_115
.It
ip6/2a00:1450:4002:803::1000_114
.It
ip6/2a00:1450:4002:803::1000_113
.It
ip6/2a00:1450:4002:803::_112
.It
ip6/2a00:1450:4002:803::_111
.El
.Pp
and so on, down to:
.Bl -bullet -width x
.It
ip6/2a00::_11
.It
ip6/2800::_10
.It
ip6/2800::_9
.It
ip6/2000::_8
.It
ip6/2000::_7
.It
ip6/2000::_6
.It
ip6/2000::_5
.It
ip6/2000::_4
.It
ip6/2000::_3
.It
ip6/::_2
.It
ip6/::_1
.It
ip6/::_0
.El
.Pp
Note that the
.Ql ip6/::_0
string is a catch-all key that matches everything.
.It
.Fn s6_accessrules_keycheck_ip46
interprets
.Va key
as a pointer to an
.Vt ip46_t Ns
[3], and behaves either as
.Fn s6_accessrules_keycheck_ip6
or
.Fn s6_accessrules_keycheck_ip4 ,
depending on the type of address
.Va *key
contains.
.El
.Ss Ready-to-use functions
These functions are mostly macros; they're built by associating a
frontend function with a backend function.
.Bl -bullet -width x
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_uidgid_cdb "uid_t u" "gid_t g" "struct cdb *c" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va *c
CDB database for an authorization for uid
.Va u
and gid
.Va g .
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_uidgid_fs "uid_t u" "gid_t g" "char const *dir" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va dir
base directory for an authorization for uid
.Va u
and gid
.Va g .
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_reversedns_cdb "char const *name" "struct cdb *c" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va *c
CDB database for an authorization for the
.Va name
FQDN.
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_reversedns_fs "char const *name" "char const *dir" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va dir
base directory for an authorization for the
.Va name
FQDN.
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_ip4_cdb "char const *ip4" "struct cdb *c" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va *c
CDB database for an authorization for the
.Va ip4
IPv4 address (4 network byte order characters).
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_ip4_fs "char const *ip4" "char const *dir" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va dir
base directory for an authorization for the
.Va ip4
IPv4 address (4 network byte order characters).
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_ip6_cdb "char const *ip6" "struct cdb *c" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va *c
CDB database for an authorization for the
.Va ip6
IPv6 address (16 network byte order characters).
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_ip6_fs "char const *ip6" "char const *dir" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va dir
base directory for an authorization for the
.Va ip6
IPv6 address (16 network byte order characters).
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_ip46_cdb "ip46_t *ip" "struct cdb *c" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va *c
CDB database for an authorization for the
.Va ip
IP address.
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.It
.Ft s6_accessrules_result_t
.Fn s6_accessrules_ip46_fs "ip46_t const *ip" "char const *dir" "s6_accessrules_params_t *params"
.Pp
Checks the
.Va dir
base directory for an authorization for the
.Va ip
IP address.
If the result is
.Dv S6_ACCESSRULES_ALLOW ,
additional information may be stored into
.Va params .
.El
.Sh SEE ALSO
.Xr s6-fdholder 7 ,
.Xr s6-ftrigr 7 ,
.Xr s6-ftrigw 7 ,
.Xr s6-libs6 7 ,
.Xr s6-s6lock 7
.Pp
[1]
.Lk https://skarnet.org/software/skalibs/libstddjb/stralloc.html
.Pp
[2]
.Lk https://cr.yp.to/cdb.html
.Pp
[3]
.Lk https://skarnet.org/software/skalibs/libstddjb/ip46.html
.Pp
This man page is ported from the authoritative documentation at:
.Lk https://skarnet.org/software/s6/libs6/accessrules.html
.Sh AUTHORS
.An Laurent Bercot
.An Alexis Ao Mt flexibeast@gmail.com Ac (man page port)