selabel_file(5) SELinux API documentation selabel_file(5)
NAME
selabel_file - userspace SELinux labeling interface and configuration
file format for the file contexts backend
SYNOPSIS
#include <selinux/label.h>
int selabel_lookup(struct selabel_handle *hnd,
char **context,
const char *path, int mode);
int selabel_lookup_raw(struct selabel_handle *hnd,
char **context,
const char *path, int mode);
DESCRIPTION
The file contexts backend maps from pathname/mode combinations into
security contexts. It is used to find the appropriate context for each
file when relabeling a file system. The returned context must be freed
using freecon(3).
selabel_lookup(3) describes the function with its return and error
codes, however the following errno is clarified further for the file
contexts backend:
ENOENT No context corresponding to the path and mode was found -
This will also be returned when the file contexts series
of files have a context of <<none>> against the path (see
the FILE FORMAT section).
The path argument should be set to the full pathname of the file whose
assigned context is being checked. The mode argument should be set to
the mode bits of the file, as determined by lstat(2). mode may be zero,
however full matching may not occur.
Any messages generated by selabel_lookup(3) are sent to stderr by
default, although this can be changed by selinux_set_callback(3).
selabel_lookup_raw(3) behaves identically to selabel_lookup(3) but does
not perform context translation.
The FILES section details the configuration files used to determine a
file context.
OPTIONS
In addition to the global options described in selabel_open(3), this
backend recognizes the following options:
SELABEL_OPT_PATH
A non-null value for this option specifies a path to a
file that will be opened in lieu of the standard file
contexts file. This value is also used as the base name
for determining the names of local customization files.
SELABEL_OPT_BASEONLY
A non-null value for this option indicates that any local
customizations to the file contexts mapping should be
ignored.
SELABEL_OPT_SUBSET
A non-null value for this option is interpreted as a path
prefix, for example "/etc". Only file context specifica-
tions with starting with a first component that prefix
matches the given prefix are loaded. This may increase
lookup performance, however any attempt to look up a path
not starting with the given prefix may fail. This opti-
mization is no longer required due to the use of
file_contexts.bin files and is deprecated.
FILES
The file context files used to retrieve the default context depends on
the SELABEL_OPT_PATH parameter passed to selabel_open(3). If NULL, then
the SELABEL_OPT_PATH value will default to the active policy file con-
texts location (as returned by selinux_file_context_path(3)), otherwise
the actual SELABEL_OPT_PATH value specified is used.
If SELABEL_OPT_BASEONLY is set, then the following files will be pro-
cessed:
1. The mandatory file contexts file that is either the fully
qualified file name from SELABEL_OPT_PATH.value or if NULL,
then the path returned by selinux_file_context_path(3).
2. The optional local and distribution substitution files that
perform path aliasing on the 'in memory' version of the file
contexts file.
These files have the same name as the mandatory file con-
texts file with the extensions .subs and .subs_dist added.
If the SELABEL_OPT_BASEONLY is not set, then the following files will
be processed:
1. The mandatory file contexts file that is either the fully
qualified file name from SELABEL_OPT_PATH.value or if NULL,
then the path returned by selinux_file_context_path(3).
2. The optional local customizations file that has the same
name as the mandatory file contexts file with the extension
.local added.
selinux_file_context_local_path(3) will return the default
path to this file.
3. The optional user home directory customizations file that
has the same name as the mandatory file contexts file with
the extension .homedirs added.
selinux_file_context_homedir_path(3) will return the default
path to this file.
4. The optional local and distribution substitution files that
perform any path aliasing on the 'in memory' version of the
file contexts file (and the .local and/or .homedirs if
present). These files have the same name as the mandatory
file contexts file with the extensions .subs and .subs_dist
added.
selinux_file_context_subs_path(3) and selinux_file_con-
text_subs_dist_path(3) will return the default paths to
these files.
The default file context series of files are:
/etc/selinux/{SELINUXTYPE}/contexts/files/file_contexts
/etc/selinux/{SELINUXTYPE}/contexts/files/file_contexts.local
/etc/selinux/{SELINUXTYPE}/contexts/files/file_contexts.homedirs
/etc/selinux/{SELINUXTYPE}/contexts/files/file_contexts.subs
/etc/selinux/{SELINUXTYPE}/contexts/files/file_contexts.subs_dist
Where {SELINUXTYPE} is the entry from the selinux configuration file
config (see selinux_config(5)).
Only the file_contexts file is mandatory, the remainder are optional.
The entries within the file contexts series of files are shown in the
FILE FORMAT section.
FILE FORMAT
File Contexts Format
Each line within the file_contexts and the two customization files
(.local and .homedirs) is as follows:
pathname [file_type] context
Where:
pathname
An entry that defines the path to be labeled. May con-
tain either a fully qualified path, or a Perl compatible
regular expression (PCRE), describing fully qualified
path(s). The only PCRE flag in use is PCRE2_DOTALL,
which causes a wildcard '.' to match anything, including
a new line. Strings representing paths are processed as
bytes (as opposed to Unicode), meaning that non-ASCII
characters are not matched by a single wildcard.
file_type
An optional file type consisting of:
-b - Block Device -c - Character Device
-d - Directory -p - Named Pipe
-l - Symbolic Link -s - Socket
-- - Ordinary file
context
This entry can be either:
a. The security context that will be assigned to
the file (i.e. returned as context).
b. A value of <<none>> can be used to indicate
that the matching files should not be re-
labeled and causes selabel_lookup(3) to return
-1 with errno set to ENOENT.
Example:
# ./contexts/files/file_contexts
# pathname file_type context
/.* system_u:object_r:default_t:s0
/[^/]+ -- system_u:object_r:etc_runtime_t:s0
/tmp/.* <<none>>
Substitution File Format
Each line within the substitution files (.subs and .subs_dist) has the
form:
subs_pathname pathname
Where:
pathname
A path that matches an entry in one or more of the file
contexts policy configuration file.
subs_pathname
The path that will be aliased (considered equivalent)
with pathname by the look up process.
Example:
# ./contexts/files/file_contexts.subs
# pathname subs_pathname
/myweb /var/www
/myspool /var/spool/mail
Using the above example, when selabel_lookup(3) is passed a path
of /myweb/index.html the function will substitute the /myweb
component with /var/www, therefore the path used is:
/var/www/index.html
NOTES
1. If contexts are to be validated, then the global option SELA-
BEL_OPT_VALIDATE must be set before calling selabel_open(3). If
this is not set, then it is possible for an invalid context to be
returned.
2. If the size of file contexts series of files contain many entries,
then selabel_open(3) may have a delay as it reads in the files, and
if requested validates the entries.
3. Depending on the version of SELinux it is possible that a file_con-
texts.template file may also be present, however this is now depre-
cated.
The template file has the same format as the file_contexts file and
may also contain the keywords HOME_ROOT, HOME_DIR, ROLE and USER.
This functionality has now been moved to the policy store and man-
aged by semodule(8) and genhomedircon(8).
SEE ALSO
selinux(8), selabel_open(3), selabel_lookup(3), selabel_stats(3),
selabel_close(3), selinux_set_callback(3),
selinux_file_context_path(3), freecon(3), selinux_config(5), lstat(2),
selinux_file_context_subs_path(3),
selinux_file_context_subs_dist_path(3),
selinux_file_context_homedir_path(3),
selinux_file_context_local_path(3), semodule(8), genhomedircon(8)
Security Enhanced Linux 01 Dec 2011 selabel_file(5)
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