108 lines
3.2 KiB
Plaintext
108 lines
3.2 KiB
Plaintext
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PROTOTYPE ACL LIBRARY
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Introduction
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An access control list (ACL) is a list of principals, where each
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principal is is represented by a text string which cannot contain
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whitespace. The library allows application programs to refer to named
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access control lists to test membership and to atomically add and
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delete principals using a natural and intuitive interface. At
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present, the names of access control lists are required to be Unix
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filenames, and refer to human-readable Unix files; in the future, when
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a networked ACL server is implemented, the names may refer to a
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different namespace specific to the ACL service.
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Usage
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cc <files> -lacl -lkrb.
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Principal Names
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Principal names have the form
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<name>[.<instance>][@<realm>]
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e.g.
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asp
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asp.root
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asp@ATHENA.MIT.EDU
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asp.@ATHENA.MIT.EDU
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asp.root@ATHENA.MIT.EDU
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It is possible for principals to be underspecified. If instance is
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missing, it is assumed to be "". If realm is missing, it is assumed
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to be local_realm. The canonical form contains all of name, instance,
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and realm; the acl_add and acl_delete routines will always
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leave the file in that form. Note that the canonical form of
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asp@ATHENA.MIT.EDU is actually asp.@ATHENA.MIT.EDU.
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Routines
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acl_canonicalize_principal(principal, buf)
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char *principal;
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char *buf; /*RETVAL*/
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Store the canonical form of principal in buf. Buf must contain enough
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space to store a principal, given the limits on the sizes of name,
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instance, and realm specified in /usr/include/krb.h.
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acl_check(acl, principal)
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char *acl;
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char *principal;
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Returns nonzero if principal appears in acl. Returns 0 if principal
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does not appear in acl, or if an error occurs. Canonicalizes
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principal before checking, and allows the ACL to contain wildcards.
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acl_exact_match(acl, principal)
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char *acl;
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char *principal;
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Like acl_check, but does no canonicalization or wildcarding.
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acl_add(acl, principal)
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char *acl;
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char *principal;
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Atomically adds principal to acl. Returns 0 if successful, nonzero
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otherwise. It is considered a failure if principal is already in acl.
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This routine will canonicalize principal, but will treat wildcards
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literally.
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acl_delete(acl, principal)
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char *acl;
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char *principal;
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Atomically deletes principal from acl. Returns 0 if successful,
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nonzero otherwise. It is consider a failure if principal is not
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already in acl. This routine will canonicalize principal, but will
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treat wildcards literally.
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acl_initialize(acl, mode)
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char *acl;
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int mode;
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Initialize acl. If acl file does not exist, creates it with mode
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mode. If acl exists, removes all members. Returns 0 if successful,
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nonzero otherwise. WARNING: Mode argument is likely to change with
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the eventual introduction of an ACL service.
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Known problems
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In the presence of concurrency, there is a very small chance that
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acl_add or acl_delete could report success even though it would have
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had no effect. This is a necessary side effect of using lock files
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for concurrency control rather than flock(2), which is not supported
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by NFS.
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The current implementation caches ACLs in memory in a hash-table
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format for increased efficiency in checking membership; one effect of
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the caching scheme is that one file descriptor will be kept open for
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each ACL cached, up to a maximum of 8.
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