selinux_status_open, selinux_status_close, selinux_status_updated,
selinux_status_getenforce, selinux_status_policyload and selinux_sta‐
tus_deny_unknown - reference the SELinux kernel status without invo‐
cation of system calls
Linux 2.6.37 or later provides a SELinux kernel status page; being
mostly placed on /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.
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.
These functions provides applications a way to know some kernel
events without system-call invocation or worker thread for
selinux_status_open() tries to open(2)/sys/fs/selinux/status and
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 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 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.
selinux_status_close() unmap the kernel status page and close its
file descriptor, or close the netlink socket if fallbacked.
selinux_status_updated() informs us whether something has been
updated since the last call. It returns 0 if nothing was happened,
however, 1 if something has been updated in this duration, or -1 on
selinux_status_getenforce() returns 0 if SELinux is running in
permissive mode, 1 if enforcing mode, or -1 on error. Same as
security_getenforce(3) except with or without system call invocation.
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
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.
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.
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.
Any other functions with a return value shall return its
characteristic value as described above, or -1 on errors.
This page is part of the selinux (Security-Enhanced Linux user-space
libraries and tools) project. Information about the project can be
found at ⟨https://github.com/SELinuxProject/selinux/wiki⟩. If you
have a bug report for this manual page, see
page was obtained from the project's upstream Git repository
⟨https://github.com/SELinuxProject/selinux⟩ on 2020-06-09. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-06-04.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to firstname.lastname@example.org
email@example.com 22 January 2011 selinux_status_open(3)