avc_has_perm(3) SELinux API documentation avc_has_perm(3)
NAME
avc_has_perm, avc_has_perm_noaudit, avc_audit, avc_entry_ref_init - ob-
tain and audit SELinux access decisions
SYNOPSIS
#include <selinux/selinux.h>
#include <selinux/avc.h>
void avc_entry_ref_init(struct avc_entry_ref *aeref);
int avc_has_perm(security_id_t ssid, security_id_t tsid,
security_class_t tclass, access_vector_t requested,
struct avc_entry_ref *aeref, void *auditdata);
int avc_has_perm_noaudit(security_id_t ssid, security_id_t tsid,
security_class_t tclass, access_vector_t requested,
struct avc_entry_ref *aeref, struct av_decision *avd);
void avc_audit(security_id_t ssid, security_id_t tsid,
security_class_t tclass, access_vector_t requested,
struct av_decision *avd, int result, void *auditdata);
DESCRIPTION
Direct use of these functions is generally discouraged in favor of the
higher level interface selinux_check_access(3) since the latter auto-
matically 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 string_to_security_class(3) and
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 SELINUX_CB_POLICYLOAD
callback set via selinux_set_callback(3).
An alternative approach is to use 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.
avc_entry_ref_init() initializes an avc_entry_ref structure; see ENTRY
REFERENCES below. This function may be implemented as a macro.
avc_has_perm() checks whether the requested permissions are granted for
subject SID ssid and target SID tsid, interpreting the permissions
based on tclass and updating aeref, if non-NULL, to refer to a cache
entry with the resulting decision. The granting or denial of permis-
sions is audited in accordance with the policy. The auditdata parame-
ter is for supplemental auditing; see avc_audit() below.
avc_has_perm_noaudit() behaves as avc_has_perm() without producing an
audit message. The access decision is returned in avd and can be
passed to avc_audit() explicitly.
avc_audit() produces an audit message for the access query represented
by ssid, tsid, tclass, and requested, with a decision represented by
avd. Pass the value returned by avc_has_perm_noaudit() as result. The
auditdata parameter is passed to the user-supplied func_audit callback
and can be used to add supplemental information to the audit message;
see avc_init(3).
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 aeref argument, if supplied, before searching the cache on a per-
mission query. After a query is performed, 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 avc_entry_ref structure, use avc_entry_ref_init() to
initialize it before passing it to avc_has_perm() or
avc_has_perm_noaudit() for the first time. Using an uninitialized
structure will produce undefined behavior.
RETURN VALUE
If requested permissions are granted, zero is returned. If requested
permissions are denied or an error occurred, -1 is returned and errno
is set appropriately.
In permissive mode, zero will be returned and errno unchanged even if
permissions were denied. avc_has_perm() will still produce an audit
message in this case.
ERRORS
EACCES A requested permission was denied.
EINVAL The tclass and/or the security contexts referenced by ssid and
tsid are not recognized by the currently loaded policy.
ENOMEM An attempt to allocate memory failed.
NOTES
Internal errors encountered by the userspace AVC may cause certain val-
ues of errno to be returned unexpectedly. For example, netlink socket
errors may produce EACCES or EINVAL. Make sure that userspace object
managers are granted appropriate access to netlink by the policy.
AUTHOR
Originally Eamon Walsh. Updated by Stephen Smalley <sds@tycho.nsa.gov>
SEE ALSO
selinux_check_access(3), string_to_security_class(3),
string_to_av_perm(3), selinux_set_callback(3), selinux_set_mapping(3),
avc_init(3), avc_context_to_sid(3), avc_cache_stats(3),
avc_add_callback(3), security_compute_av(3), selinux(8)
27 May 2004 avc_has_perm(3)
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