libselinux/man/man3/avc_has_perm.3

.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Author: Eamon Walsh (ewalsh@tycho.nsa.gov) 2004
.TH "avc_has_perm" "3" "27 May 2004" "" "SELinux 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"

Direct use of these functions is generally discouraged in favor of
the higher level interface
.BR selinux_check_access(3)
since the latter automatically handles the dynamic mapping of class
and permission names to their policy values and proper handling of
allow_unknown.

When using any of the functions that take policy integer values for
classes or permissions as inputs, use
.BR string_to_security_class(3)
and
.BR string_to_av_perm(3)
to map the class and permission names to their policy values.
These values may change across a policy reload, so they should be
re-acquired on every use or using a
.B SELINUX_CB_POLICYLOAD
callback set via
.BR selinux_set_callback(3).

An alternative approach is to use
.BR selinux_set_mapping(3)
to create a mapping from class and permission index values
used by the application to the policy values,
thereby allowing the application to pass its own
fixed constants for the classes and permissions to
these functions and internally mapping them on demand.
However, this also requires setting up a callback as above
to address policy reloads.

.BR avc_entry_ref_init ()
initializes an
.B avc_entry_ref
structure; see
.B ENTRY REFERENCES
below.  This function may be implemented as a macro.

.BR 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
.BR avc_audit ()
below.

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

.BR 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
.BR 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
.BR avc_entry_ref_init ()
to initialize it before passing it to
.BR avc_has_perm ()
or
.BR \%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 occurred, \-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.
.BR 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"
Originally Eamon Walsh.  Updated by Stephen Smalley <sds@tycho.nsa.gov>
.
.SH "SEE ALSO"
.ad l
.nh
.BR selinux_check_access(3),
.BR string_to_security_class(3),
.BR string_to_av_perm(3),
.BR selinux_set_callback(3),
.BR selinux_set_mapping(3),
.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),
.BR selinux (8)