libselinux/man/man3/selinux_status_open.3

.TH "selinux_status_open" "3" "22 January 2011" "kaigai@ak.jp.nec.com" "SELinux API documentation"
.SH "NAME"
selinux_status_open, selinux_status_close, selinux_status_updated,
selinux_status_getenforce, selinux_status_policyload and
selinux_status_deny_unknown \- reference the SELinux kernel status
without invocation of system calls
.
.SH "SYNOPSIS"
.B #include <selinux/avc.h>
.sp
.BI "int selinux_status_open(int " fallback ");"
.sp
.BI "void selinux_status_close(void);"
.sp
.BI "int selinux_status_updated(void);"
.sp
.BI "int selinux_status_getenforce(void);"
.sp
.BI "int selinux_status_policyload(void);"
.sp
.BI "int selinux_status_deny_unknown(void);"
.
.SH "DESCRIPTION"
Linux 2.6.37 or later provides a SELinux kernel status page; being mostly
placed on
.I /sys/fs/selinux/status
entry. It enables userspace applications to mmap this page with read-only
mode, then it informs some status without system call invocations.
.sp
In some cases that a userspace application tries to apply heavy frequent
access control; such as row-level security in databases, it will face
unignorable cost to communicate with kernel space to check invalidation
of userspace avc.
.sp
These functions provides applications a way to know some kernel events
without system-call invocation or worker thread for monitoring.
.sp
.BR selinux_status_open ()
tries to
.BR open (2)
.I /sys/fs/selinux/status
and
.BR mmap (2)
it in read-only mode. The file-descriptor and pointer to the page shall
be stored internally; Don't touch them directly.
Set 1 on the
.I fallback
argument to handle a case of older kernels without kernel status page support.
In this case, this function tries to open a netlink socket using
.BR avc_netlink_open (3)
and overwrite corresponding callbacks (setenforce and policyload).
Thus, we need to pay attention to the interaction with these interfaces,
when fallback mode is enabled.
.sp
.BR selinux_status_close ()
unmap the kernel status page and close its file descriptor, or close the
netlink socket if fallbacked.
.sp
.BR selinux_status_updated ()
processes status update events. There are two kinds of status updates.
.B setenforce
events will change the effective enforcing state used within the AVC, and
.B policyload
events will result in a cache flush.

This function returns 0 if there have been no updates since the last call,
1 if there have been updates since the last call, or \-1 on error.
.sp
.BR selinux_status_getenforce ()
returns 0 if SELinux is running in permissive mode, 1 if enforcing mode,
or \-1 on error.
Same as
.BR security_getenforce (3)
except with or without system call invocation.
.sp
.BR selinux_status_policyload ()
returns times of policy reloaded on the running system, or \-1 on error.
Note that it is not a reliable value on fallback-mode until it receive
the first event message via netlink socket.
Thus, don't use this value to know actual times of policy reloaded.
.sp
.BR selinux_status_deny_unknown ()
returns 0 if SELinux treats policy queries on undefined object classes or
permissions as being allowed, 1 if such queries are denied, or \-1 on error.
.sp
Also note that these interfaces are not thread-safe, so you have to protect
them from concurrent calls using exclusive locks when multiple threads are
performing.
.
.SH "RETURN VALUE"
.BR selinux_status_open ()
returns 0 or 1 on success. 1 means we are ready to use these interfaces,
but netlink socket was opened as fallback instead of the kernel status page.
On error, \-1 shall be returned.
.sp
Any other functions with a return value shall return its characteristic
value as described above, or \-1 on errors.
.
.SH "SEE ALSO"
.ad l
.nh
.BR mmap (2),
.BR avc_netlink_open (3),
.BR security_getenforce (3),
.BR security_deny_unknown (3)