.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Author: Eamon Walsh (ewalsh@epoch.ncsc.mil) 2004
.TH "avc_has_perm" "3" "27 May 2004" "" "SE Linux API documentation"
.SH "NAME"
avc_has_perm, avc_has_perm_noaudit, avc_audit, avc_entry_ref_init \- obtain and audit SELinux access decisions.
.SH "SYNOPSIS"
.B #include <selinux/selinux.h>
.br
.B #include <selinux/avc.h>
.sp
.BI "void avc_entry_ref_init(struct avc_entry_ref *" aeref ");"
.sp
.BI "int avc_has_perm(security_id_t " ssid ", security_id_t " tsid ,
.in +\w'int avc_has_perm('u
.BI "security_class_t " tclass ", access_vector_t " requested ,
.br
.BI "struct avc_entry_ref *" aeref ", void *" auditdata ");"
.in
.sp
.BI "int avc_has_perm_noaudit(security_id_t " ssid ", security_id_t " tsid ,
.in +\w'int avc_has_perm('u
.BI "security_class_t " tclass ", access_vector_t " requested ,
.br
.BI "struct avc_entry_ref *" aeref ", struct av_decision *" avd ");"
.in
.sp
.BI "void avc_audit(security_id_t " ssid ", security_id_t " tsid ,
.in +\w'void avc_audit('u
.BI "security_class_t " tclass ", access_vector_t " requested ,
.br
.BI "struct av_decision *" avd ", int " result ", void *" auditdata ");"
.in
.SH "DESCRIPTION"
.B avc_entry_ref_init
initializes an
.B avc_entry_ref
structure; see
.B ENTRY REFERENCES
below.  This function may be implemented as a macro.

.B avc_has_perm
checks whether the 
.I requested
permissions are granted
for subject SID
.IR ssid
and target SID
.IR tsid ,
interpreting the permissions
based on
.I tclass
and updating
.IR aeref ,
if non-NULL, to refer to a cache entry with the resulting decision.  The granting or denial of permissions is audited in accordance with the policy.  The
.I auditdata
parameter is for supplemental auditing; see
.B avc_audit
below.

.B avc_has_perm_noaudit
behaves as
.B avc_has_perm
without producing an audit message.  The access decision is returned in
.I avd
and can be passed to
.B avc_audit
explicitly.

.B avc_audit
produces an audit message for the access query represented by
.IR ssid ,
.IR tsid ,
.IR tclass ,
and
.IR requested ,
with a decision represented by
.IR avd .
Pass the value returned by
.B avc_has_perm_noaudit
as
.IR result .
The
.I auditdata
parameter is passed to the user-supplied
.B func_audit
callback and can be used to add supplemental information to the audit message; see
.BR avc_init (3).

.SH "ENTRY REFERENCES"
Entry references can be used to speed cache performance for repeated queries on the same subject and target.  The userspace AVC will check the
.I aeref
argument, if supplied, before searching the cache on a permission query.  After a query is performed,
.I aeref
will be updated to reference the cache entry for that query.  A subsequent query on the same subject and target will then have the decision at hand without having to walk the cache.

After declaring an
.B avc_entry_ref
structure, use
.B avc_entry_ref_init
to initialize it before passing it to
.B avc_has_perm
or
.B avc_has_perm_noaudit
for the first time.
Using an uninitialized structure will produce undefined behavior.

.SH "RETURN VALUE"
If requested permissions are granted, zero is returned.  If requested permissions are denied or an error occured, \-1 is returned and
.I errno
is set appropriately.

In permissive mode, zero will be returned and
.I errno
unchanged even if permissions were denied.
.B avc_has_perm
will still produce an audit message in this case.

.SH "ERRORS"
.TP
.B EACCES
A requested permission was denied.
.TP
.B EINVAL
The
.I tclass
and/or the security contexts referenced by
.I ssid
and
.I tsid
are not recognized by the currently loaded policy.
.TP
.B ENOMEM
An attempt to allocate memory failed.

.SH "NOTES"
Internal errors encountered by the userspace AVC may cause certain values of
.I errno
to be returned unexpectedly.  For example, netlink socket errors may produce
.B EACCES
or
.BR EINVAL .
Make sure that userspace object managers are granted appropriate access to
netlink by the policy.

.SH "AUTHOR"
Eamon Walsh <ewalsh@epoch.ncsc.mil>

.SH "SEE ALSO"
.BR avc_init (3),
.BR avc_context_to_sid (3),
.BR avc_cache_stats (3),
.BR avc_add_callback (3),
.BR security_compute_av (3)