avc_open(3) SELinux API documentation avc_open(3)
NAME
avc_open, avc_destroy, avc_reset, avc_cleanup - userspace SELinux AVC
setup and teardown
SYNOPSIS
#include <selinux/selinux.h>
#include <selinux/avc.h>
int avc_open(struct selinux_opt *options, unsigned nopt);
void avc_destroy(void);
int avc_reset(void);
void avc_cleanup(void);
DESCRIPTION
avc_open() initializes the userspace AVC and must be called before any
other AVC operation can be performed.
avc_destroy() destroys the userspace AVC, freeing all internal memory
structures. After this call has been made, avc_open() must be called
again before any AVC operations can be performed. avc_destroy() also
closes the SELinux status page, which might have been opened manually
by selinux_status_open(3).
avc_reset() flushes the userspace AVC, causing it to forget any cached
access decisions. The userspace AVC normally calls this function auto-
matically when needed, see NETLINK NOTIFICATION below.
avc_cleanup() attempts to free unused memory within the userspace AVC,
but does not flush any cached access decisions. Under normal opera-
tion, calling this function should not be necessary.
OPTIONS
The userspace AVC obeys callbacks set via selinux_set_callback(3), in
particular the logging and audit callbacks.
The options which may be passed to avc_open() include the following:
AVC_OPT_SETENFORCE
This option forces the userspace AVC into enforcing mode if the
option value is non-NULL; permissive mode otherwise. The system
enforcing mode will be ignored.
KERNEL STATUS PAGE
Linux kernel version 2.6.37 supports the SELinux kernel status page,
enabling userspace applications to mmap(2) SELinux status state in
read-only mode to avoid system calls during the cache hit code path.
avc_open() calls selinux_status_open(3) to initialize the selinux sta-
tus state.
avc_has_perm(3) and selinux_check_access(3) both check for status up-
dates through calls to selinux_status_updated(3) at the start of each
permission query and take the appropriate action.
Two status types are currently implemented. setenforce events will
change the effective enforcing state used within the AVC, and policy-
load events will result in a cache flush.
NETLINK NOTIFICATION
In the event that the kernel status page is not successfully mmap(2)'ed
the AVC will default to the netlink fallback mechanism, which opens a
netlink socket for receiving status updates. setenforce and policyload
events will have the same results as for the status page implementa-
tion, but all status update checks will now require a system call.
RETURN VALUE
Functions with a return value return zero on success. On error, -1 is
returned and errno is set appropriately.
AUTHOR
Eamon Walsh <ewalsh@tycho.nsa.gov>
SEE ALSO
selinux(8), selinux_check_access(3), avc_has_perm(3), avc_con-
text_to_sid(3), avc_cache_stats(3), avc_add_callback(3), selinux_sta-
tus_open(3), selinux_status_updated(3), selinux_set_callback(3), secu-
rity_compute_av(3)
12 Jun 2008 avc_open(3)
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