ACL_CHECK(3)

NAME
acl_canonicalize_principal, acl_check, acl_exact_match, acl_add, acl_delete, acl_initialize - Access control list routines

SYNOPSIS
cc <files> -lacl -lkrb

#include <krb.h>

acl_canonicalize_principal(principal, buf)
char *principal;
char *buf;

acl_check(acl, principal)
char *acl;
char *principal;

acl_exact_match(acl, principal)
char *acl;
char *principal;

acl_add(acl, principal)
char *acl;
char *principal;

acl_delete(acl, principal)
char *acl;
char *principal;

acl_initialize(acl_file, mode)
char *acl_file;
int mode;

DESCRIPTION

  Introduction

An access control list (ACL) is a list of principals, where each principal is represented by a text string which cannot contain whitespace. The library allows application programs to refer to named access control lists to test membership and to atomically add and delete principals using a natural and intuitive interface. At present, the names of access control lists are required to be Unix filenames, and refer to human-readable Unix files; in the future, when a networked ACL server is implemented, the names may refer to a different namespace specific to the ACL service.

  Principal Names

Principal names have the form
<name>[.<instance>][@<realm>]
e.g.:
asp
asp.root
asp@ATHENA.MIT.EDU
asp.@ATHENA.MIT.EDU
asp.root@ATHENA.MIT.EDU
It is possible for principals to be underspecified. If an instance is missing, it is assumed to be "". If realm is missing, it is assumed to be the local realm as determined by krb_get_lrealm(3). The canonical form contains all of name, instance, and realm; the acl_add and acl_delete routines will always leave the file in that form. Note that the canonical form of asp@ATHENA.MIT.EDU is actually asp.@ATHENA.MIT.EDU.

  Routines

acl_canonicalize_principal stores the canonical form of principal in buf. Buf must contain enough space to store a principal, given the limits on the sizes of name, instance, and realm specified as ANAME_SZ, INST_SZ, and REALM_SZ, respectively, in /usr/include/krb.h.

acl_check returns nonzero if principal appears in acl. Returns 0 if principal does not appear in acl, or if an error occurs. Canonicalizes principal before checking, and allows the ACL to contain wildcards. The only supported wildcards are entries of the form name.*@realm, *.*@realm, and *.*@*. An asterisk matches any value for the its component field. For example, "jtkohl.*@*" would match principal jtkohl, with any instance and any realm.

acl_exact_match performs like acl_check, but does no canonicalization or wildcard matching.

acl_add atomically adds principal to acl. Returns 0 if successful, nonzero otherwise. It is considered a failure if principal is already in acl. This routine will canonicalize principal, but will treat wildcards literally.

acl_delete atomically deletes principal from acl. Returns 0 if successful, nonzero otherwise. It is considered a failure if principal is not already in acl. This routine will canonicalize principal, but will treat wildcards literally.

acl_initialize initializes acl_file. If the file acl_file does not exist, acl_initialize creates it with mode mode. If the file acl_file exists, acl_initialize removes all members. Returns 0 if successful, nonzero otherwise. WARNING: Mode argument is likely to change with the eventual introduction of an ACL service.

NOTES
In the presence of concurrency, there is a very small chance that acl_add or acl_delete could report success even though it would have had no effect. This is a necessary side effect of using lock files for concurrency control rather than flock(2), which is not supported by NFS.

The current implementation caches ACLs in memory in a hash-table format for increased efficiency in checking membership; one effect of the caching scheme is that one file descriptor will be kept open for each ACL cached, up to a maximum of 8.

SEE ALSO
kerberos(3), krb_get_lrealm(3)

AUTHOR
James Aspnes (MIT Project Athena)