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05bdc03130
Commit bc2a8f418e ("libselinux: add selinux_status_* interfaces for
/selinux/status") introduced the sestatus mechanism, which allows for
mmap()'ing of the kernel status page as a replacement for avc_netlink.
The mechanism was initially intended for userspace object managers that
were calculating access decisions within their application and did not
rely on the libselinux AVC implementation. In order to properly make use
of sestatus within avc_has_perm(), the status mechanism needs to
properly set avc internals during status events; else, avc_enforcing is
never updated upon sestatus changes.
This commit gets rid of the default avc_netlink_open() in
avc_init_internal(), replacing it with selinux_status_open(). In the
event that the kernel status page cannot be mapped, the netlink fallback
will be used. By default, avc_has_perm_noaudit() and
selinux_check_access() will now attempt to read the kernel status page,
which removes a system call from two critical code paths.
Since the AVC thread create/stop callbacks were intended to avoid a
system call in the critical code path, they no longer need to be created
by default. In the event that the kernel status page is successfully
mapped, threads will not be created. Threads will still be
created/stopped for the sestatus fallback codepaths.
Userspace object managers that still need a netlink socket can call
avc_netlink_acquire_fd() to open and/or obtain one.
Update the manpage to reflect the new avc_netlink_acquire_fd()
functionality.
Signed-off-by: Mike Palmiotto <mike.palmiotto@crunchydata.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
93 lines
2.9 KiB
Groff
93 lines
2.9 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Author: KaiGai Kohei (kaigai@ak.jp.nec.com) 2009
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.TH "avc_netlink_loop" "3" "30 Mar 2009" "" "SELinux API documentation"
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.SH "NAME"
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avc_netlink_open, avc_netlink_close, avc_netlink_acquire_fd,
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avc_netlink_release_fd, avc_netlink_check_nb, avc_netlink_loop \- SELinux
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netlink processing
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.
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.SH "SYNOPSIS"
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.B #include <selinux/selinux.h>
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.br
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.B #include <selinux/avc.h>
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.sp
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.BI "int avc_netlink_open(int " blocking ");"
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.sp
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.B void avc_netlink_close(void);
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.sp
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.B int avc_netlink_acquire_fd(void);
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.sp
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.B void avc_netlink_release_fd(void);
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.sp
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.B void avc_netlink_loop(void);
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.sp
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.B int avc_netlink_check_nb(void);
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.
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.SH "DESCRIPTION"
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These functions enable applications to handle notification of SELinux events
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via netlink. The userspace AVC normally checks for netlink messages on each
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call to
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.BR avc_has_perm (3).
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Applications may wish to override this behavior and check for notification
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separately, for example in a
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.BR select (2)
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loop. These functions also permit netlink monitoring without requiring a
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call to
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.BR avc_open (3).
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.BR avc_netlink_open ()
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opens a netlink socket to receive SELinux notifications. The socket
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descriptor is stored internally; use
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.BR avc_netlink_acquire_fd (3)
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to take ownership of it in application code. The
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.I blocking
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argument controls whether the O_NONBLOCK flag is set on the socket descriptor.
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.BR avc_open (3)
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calls this function internally, specifying non-blocking behavior.
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.BR avc_netlink_close ()
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closes the netlink socket. This function is called automatically by
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.BR avc_destroy (3).
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.BR avc_netlink_acquire_fd ()
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returns the netlink socket descriptor number and informs the userspace AVC
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not to check the socket descriptor automatically on calls to
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.BR avc_has_perm (3).
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If no such socket descriptor exists,
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.BR avc_netlink_acquire_fd (3)
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will first call
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.BR avc_netlink_open (3)
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and then return the resulting fd.
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.BR avc_netlink_release_fd ()
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returns control of the netlink socket to the userspace AVC, re-enabling
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automatic processing of notifications.
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.BR avc_netlink_check_nb ()
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checks the netlink socket for pending messages and processes them.
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Callbacks for policyload and enforcing changes will be called;
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see
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.BR selinux_set_callback (3).
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This function does not block.
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.BR avc_netlink_loop ()
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enters a loop blocking on the netlink socket and processing messages as they
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are received. This function will not return unless an error occurs on
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the socket, in which case the socket is closed.
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.
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.SH "RETURN VALUE"
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.BR avc_netlink_acquire_fd ()
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returns a non-negative file descriptor number on success. Other functions
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with a return value return zero on success. On error, \-1 is returned and
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.I errno
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is set appropriately.
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.
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.SH "AUTHOR"
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Originally KaiGai Kohei. Updated by Mike Palmiotto <mike.palmiotto@crunchydata.com>
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.
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.SH "SEE ALSO"
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.BR avc_open (3),
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.BR selinux_set_callback (3),
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.BR selinux (8)
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