Ubuntu Manpage: selabel_file - userspace SELinux labeling interface and configuration file format for the

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 specifications 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 optimization 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 contexts 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 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 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 contexts 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_context_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 contain  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 SELABEL_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_contexts.template  file
           may also be present, however this is now deprecated.
           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 managed by semodule(8) and genhomedircon(8).