libselinux/man/man3/security_compute_av.3

.TH "security_compute_av" "3" "1 January 2004" "russell@coker.com.au" "SELinux API documentation"
.SH "NAME"
security_compute_av, security_compute_av_flags, security_compute_create, security_compute_create_name, security_compute_relabel,
security_compute_member, security_compute_user, security_validatetrans, security_get_initial_context \- query
the SELinux policy database in the kernel
.
.SH "SYNOPSIS"
.B #include <selinux/selinux.h>
.sp
.BI "int security_compute_av(char *" scon ", char *" tcon ", security_class_t "tclass ", access_vector_t "requested ", struct av_decision *" avd );
.sp
.BI "int security_compute_av_raw(char *" scon ", char *" tcon ", security_class_t "tclass ", access_vector_t "requested ", struct av_decision *" avd );
.sp
.BI "int security_compute_av_flags(char *" scon ", char *" tcon ", security_class_t "tclass ", access_vector_t "requested ", struct av_decision *" avd );
.sp
.BI "int security_compute_av_flags_raw(char *" scon ", char *" tcon ", security_class_t "tclass ", access_vector_t "requested ", struct av_decision *" avd );
.sp
.BI "int security_compute_create(char *" scon ", char *" tcon ", security_class_t "tclass ", char **" newcon );
.sp
.BI "int security_compute_create_raw(char *" scon ", char *" tcon ", security_class_t "tclass ", char **" newcon );
.sp
.BI "int security_compute_create_name(char *" scon ", char *" tcon ", security_class_t "tclass ", const char *" objname ", char **" newcon );
.sp
.BI "int security_compute_create_name_raw(char *" scon ", char *" tcon ", security_class_t "tclass ", const char *" objname ", char **" newcon );
.sp
.BI "int security_compute_relabel(char *" scon ", char *" tcon ", security_class_t "tclass ", char **" newcon );
.sp
.BI "int security_compute_relabel_raw(char *" scon ", char *" tcon ", security_class_t "tclass ", char **" newcon );
.sp
.BI "int security_compute_member(char *" scon ", char *" tcon ", security_class_t "tclass ", char **" newcon );
.sp
.BI "int security_compute_member_raw(char *" scon ", char *" tcon ", security_class_t "tclass ", char **" newcon );
.sp
.BI "int security_compute_user(char *" scon ", const char *" username ", char ***" con );
.sp
.BI "int security_compute_user_raw(char *" scon ", const char *" username ", char ***" con );
.sp
.BI "int security_validatetrans(char *" scon ", const char *" tcon ", security_class_t "tclass ", char *" newcon );
.sp
.BI "int security_validatetrans_raw(char *" scon ", const char *" tcon ", security_class_t "tclass ", char *" newcon );
.sp
.BI "int security_get_initial_context(const char *" name ", char **" con );
.sp
.BI "int security_get_initial_context_raw(const char *" name ", char **" con );
.sp
.BI "int selinux_check_access(const char *" scon ", const char *" tcon ", const char *" class ", const char *" perm ", void *" auditdata);
.sp
.BI "int selinux_check_passwd_access(access_vector_t " requested );
.sp
.BI "int checkPasswdAccess(access_vector_t " requested );
.
.SH "DESCRIPTION"

This family of functions is used to obtain policy decisions from the
SELinux kernel security server (policy engine).  In general, direct use of
.BR security_compute_av ()
and its variant interfaces is discouraged in favor of using
.BR selinux_check_access ()
since the latter automatically handles the dynamic mapping of class
and permission names to their policy values, initialization and use of
the Access Vector Cache (AVC), and proper handling of per-domain and
global permissive mode and 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 security_compute_av ()
queries whether the policy permits the source context
.I scon
to access the target context
.I tcon
via class
.I tclass
with the
.I requested
access vector.  The decision is returned in
.IR avd .

.BR security_compute_av_flags ()
is identical to
.B security_compute_av
but additionally sets the
.I flags
field of
.IR avd .
Currently one flag is supported:
.BR SELINUX_AVD_FLAGS_PERMISSIVE ,
which indicates the decision is computed on a permissive domain.

.BR security_compute_create ()
is used to compute a context to use for labeling a new object in a particular
class based on a SID pair.

.BR security_compute_create_name ()
is identical to
.BR \%security_compute_create ()
but also takes name of the new object in creation as an argument.
When
.B TYPE_TRANSITION
rule on the given class and a SID pair has object name extension,
we shall be able to obtain a correct
.I newcon
according to the security policy. Note that this interface is only
supported on the linux 2.6.40 or later.
In the older kernel, the object name will be simply ignored.

.BR security_compute_relabel ()
is used to compute the new context to use when relabeling an object, it is used
in the pam_selinux.so source and the newrole source to determine the correct
label for the tty at login time, but can be used for other things.

.BR security_compute_member ()
is used to compute the context to use when labeling a polyinstantiated object
instance.

.BR security_compute_user ()
is used to determine the set of user contexts that can be reached from a
source context. It is mainly used by
.BR get_ordered_context_list (3).

.BR security_validatetrans ()
is used to determine if a transition from scon to newcon using tcon as the object
is valid for object class tclass. This checks against the mlsvalidatetrans and
validatetrans constraints in the loaded policy. Returns 0 if allowed, and -1
if an error occurred with errno set.

.BR security_get_initial_context ()
is used to get the context of a kernel initial security identifier specified by 
.I name

.BR security_compute_av_raw (),
.BR security_compute_av_flags_raw (),
.BR \%security_compute_create_raw (),
.BR \%security_compute_create_name_raw (),
.BR \%security_compute_relabel_raw (),
.BR \%security_compute_member_raw (),
.BR \%security_compute_user_raw ()
.BR \%security_validatetrans_raw ()
and
.BR \%security_get_initial_context_raw ()
behave identically to their non-raw counterparts but do not perform context
translation.

.BR selinux_check_access ()
is used to check if the source context has the access permission for the specified class on the target context.

.BR selinux_check_passwd_access ()
is used to check for a permission in the
.I passwd
class.
.BR selinux_check_passwd_access ()
uses
.BR getprevcon(3)
for the source and target security contexts.

.BR checkPasswdAccess ()
is a deprecated alias of the
.BR selinux_check_passwd_access ()
function.
.
.SH "RETURN VALUE"
Returns zero on success or \-1 on error.
.
.SH "SEE ALSO"
.BR string_to_security_class (3),
.BR string_to_av_perm (3),
.BR selinux_set_callback (3),
.BR selinux_set_mapping (3),
.BR getprevcon (3),
.BR get_ordered_context_list (3),
.BR selinux (8)