Security-Enhanced Linux secures the thumb processes via flexible mandatory access control.
The thumb processes execute with the thumb_t SELinux type. You can check if you have these processes running by executing the ps command with the -Z qualifier.
ps -eZ | grep thumb_t
The thumb_t SELinux type can be entered via the thumb_exec_t file type.
The default entrypoint paths for the thumb_t domain are the following:
/usr/bin/[^/]*thumbnailer, /usr/bin/gnome-[^/]*-thumbnailer(.sh)?, /usr/lib/tumbler-?[^/]*/tumblerd, /usr/bin/raw-thumbnailer, /usr/bin/ffmpegthumbnailer, /usr/bin/whaaw-thumbnailer, /usr/bin/evince-thumbnailer, /usr/bin/mate-thumbnail-font, /usr/bin/gnome-thumbnail-font, /usr/bin/gsf-office-thumbnailer, /usr/bin/totem-video-thumbnailer, /usr/bin/shotwell-video-thumbnailer
You can see the context of a process using the -Z option to psP Policy governs the access confined processes have to files. SELinux thumb policy is very flexible allowing users to setup their thumb processes in as secure a method as possible.
The following process types are defined for thumb:
Note: semanage permissive -a thumb_t can be used to make the process type thumb_t permissive. SELinux does not deny access to permissive process types, but the AVC (SELinux denials) messages are still generated.
If you want to deny user domains applications to map a memory region as both executable and writable, this is dangerous and the executable should be reported in bugzilla, you must turn on the deny_execmem boolean. Disabled by default.
setsebool -P deny_execmem 1
If you want to allow all domains to execute in fips_mode, you must turn on the fips_mode boolean. Enabled by default.
setsebool -P fips_mode 1
If you want to allow all unconfined executables to use libraries requiring text relocation that are not labeled textrel_shlib_t, you must turn on the selinuxuser_execmod boolean. Enabled by default.
setsebool -P selinuxuser_execmod 1
If you want to support NFS home directories, you must turn on the use_nfs_home_dirs boolean. Disabled by default.
setsebool -P use_nfs_home_dirs 1
If you want to support SAMBA home directories, you must turn on the use_samba_home_dirs boolean. Disabled by default.
setsebool -P use_samba_home_dirs 1
The SELinux process type thumb_t can manage files labeled with the following file types. The paths listed are the default paths for these file types. Note the processes UID still need to have DAC permissions.
You can see the context of a file using the -Z option to lsP Policy governs the access confined processes have to these files. SELinux thumb policy is very flexible allowing users to setup their thumb processes in as secure a method as possible.
STANDARD FILE CONTEXT
SELinux defines the file context types for the thumb, if you wanted to store files with these types in a diffent paths, you need to execute the semanage command to sepecify alternate labeling and then use restorecon to put the labels on disk.
semanage fcontext -a -t thumb_tmpfs_t '/srv/mythumb_content(/.*)?'
restorecon -R -v /srv/mythumb_content
Note: SELinux often uses regular expressions to specify labels that match multiple files.
The following file types are defined for thumb:
- Set files with the thumb_exec_t type, if you want to transition an executable to the thumb_t domain.
- Set files with the thumb_home_t type, if you want to store thumb files in the users home directory.
- Set files with the thumb_tmp_t type, if you want to store thumb temporary files in the /tmp directories.
- Set files with the thumb_tmpfs_t type, if you want to store thumb files on a tmpfs file system.
Note: File context can be temporarily modified with the chcon command. If you want to permanently change the file context you need to use the semanage fcontext command. This will modify the SELinux labeling database. You will need to use restorecon to apply the labels.
semanage permissive can also be used to manipulate whether or not a process type is permissive.
semanage module can also be used to enable/disable/install/remove policy modules.
semanage boolean can also be used to manipulate the booleans
system-config-selinux is a GUI tool available to customize SELinux policy settings.