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xsecurelock
1.7.0
XSecureLock is an X11 screen lock utility.
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XSecureLock is an X11 screen lock utility designed with the primary goal of security.
Screen lock utilities are widespread. However, in the past they often had security issues regarding authentication bypass (a crashing screen locker would unlock the screen), information disclosure (notifications may appear on top of the screen saver), or sometimes even worse.
In XSecureLock, security is achieved using a modular design to avoid the usual pitfalls of screen locking utility design on X11. Details are available in the Security Design section.
The following packages need to be installed; their names depend on your Linux distribution of choice, but will be similar:
auth_htpasswd module)authproto_pam module)saver_mplayer module)saver_mpv module)authproto_pamtester module)saver_xscreensaver module)NOTE: In these instructions, please replace SERVICE-NAME by the name of an appropriate and existing file in /etc/pam.d. If xscreensaver is installed, xscreensaver should always be a good choice; otherwise, on Debian and Ubuntu, common-auth would work. This will be used as default and can be overridden with XSECURELOCK_PAM_SERVICE.
Configuring a broken or missing SERVICE-NAME will render unlocking the screen impossible! If this should happen to you, switch to another terminal (Ctrl-Alt-F1), log in there, and run: killall xsecurelock to force unlocking of the screen.
First of all, on BSD systems, /usr/local is owned by the ports system, so unless you are creating a port, it is recommended to install to a separate location by specifying something like --prefix=/opt/xsecurelock in the ./configure call. You can then run XSecureLock as /opt/xsecurelock/bin/xsecurelock.
Also, in order to authenticate with PAM on FreeBSD and NetBSD, you must be root so you can read the shadow password database. The authproto_pam binary can be made to acquire these required privileges like this:
First of all, on BSD systems, /usr/local is owned by the ports system, so unless you are creating a port, it is recommended to install to a separate location by specifying something like --prefix=/opt/xsecurelock in the ./configure call. You can then run XSecureLock as /opt/xsecurelock/bin/xsecurelock.
Also, in order to authenticate with PAM on OpenBSD, you must be in the auth group so you can run a setuid helper called login_passwd that can read the shadow password database. The authproto_pam binary can be made to acquire these required privileges like this:
Note that this adds substantially less attack surface than adding your own user to the auth group, as the login_passwd binary can try out passwords of any user, while authproto_pam is restricted to trying your own user.
Pick one of the authentication modules and one of the screen saver modules.
Tell your desktop environment to run XSecureLock by using a command line such as one of the following:
Just kidding about the last one :)
IMPORTANT: Make sure your desktop environment does not launch any other locker, be it via autostart file or its own configuration, as multiple screen lockers may interfere with each other. You have been warned!
To automatically lock the screen after some time of inactivity, use xss-lock as follows:
The option -l is critical as it makes sure not to allow machine suspend before the screen saver is active - otherwise previous screen content may show up for a short time after wakeup!
NOTE: When using xss-lock, it's recommended to not launch xsecurelock directly for manual locking, but to manually lock using xset s activate. This ensures that xss-lock knows about the locking state and won't try again, which would spam the X11 error log.
WARNING: Never rely on automatic locking for security, for the following reasons:
Automatic locking should merely be seen as a fallback for the case of the user forgetting to lock explicitly, and not as a security feature. If you really want to use this as a security feature, make sure to kill the session whenever attempts to lock fail (in which case xsecurelock will return a non-zero exit status).
xautolock can be used instead of xss-lock as long as you do not care for suspend events (like on laptops):
Ideally, an environment integrating xsecurelock should provide the following facilities:
dimmer.dimmer and go back to the start.dimmer exits, run xsecurelock and wait for it.xsecurelock and wait for it.xsecurelock while passing along XSS_SLEEP_LOCK_FD and wait for it.This is, of course precisely what xss-lock does, and - apart from the suspend handling - what xautolock does.
As an alternative, we also support this way of integrating:
until_nonidle dimmer || exec xsecurelock and wait for it."IDLETIME" timer, as this command can never exit without those being reset).xsecurelock and wait for it.xsecurelock while passing along XSS_SLEEP_LOCK_FD and wait for it.NOTE: When using until_nonidle with other dimming tools than the included dimmer, please set XSECURELOCK_DIM_TIME_MS and XSECURELOCK_WAIT_TIME_MS to match the time your dimming tool takes for dimming, and how long you want to wait in dimmed state before locking.
Options to XSecureLock can be passed by environment variables:
XSECURELOCK_AUTH: specifies the desired authentication module (the part that displays the authentication prompt).XSECURELOCK_AUTHPROTO: specifies the desired authentication protocol module (the part that talks to the system).XSECURELOCK_AUTH_BACKGROUND_COLOR: specifies the X11 color (see manpage of XParseColor) for the background of the auth dialog.XSECURELOCK_AUTH_CURSOR_BLINK: if set, the cursor will blink in the auth dialog. Enabled by default, can be set to 0 to disable.XSECURELOCK_AUTH_SOUNDS: specifies whether to play sounds during authentication to indicate status. Sounds are defined as follows:XSECURELOCK_AUTH_FOREGROUND_COLOR: specifies the X11 color (see manpage of XParseColor) for the foreground text of the auth dialog.XSECURELOCK_AUTH_TIMEOUT: specifies the time (in seconds) to wait for response to a prompt by auth_x11 before giving up and reverting to the screen saver.XSECURELOCK_AUTH_WARNING_COLOR: specifies the X11 color (see manpage of XParseColor) for the warning text of the auth dialog.XSECURELOCK_BLANK_TIMEOUT: specifies the time (in seconds) before telling X11 to fully blank the screen; a negative value disables X11 blanking. The time is measured since the closing of the auth window or xsecurelock startup. Setting this to 0 is rather nonsensical, as key-release events (e.g. from the keystroke to launch xsecurelock or from pressing escape to close the auth dialog) always wake up the screen.XSECURELOCK_BLANK_DPMS_STATE: specifies which DPMS state to put the screen in when blanking (one of standby, suspend, off and on, where "on" means to not invoke DPMS at all).XSECURELOCK_BURNIN_MITIGATION: specifies the number of pixels the prompt of auth_x11 may be moved at startup to mitigate possible burn-in effects due to the auth dialog being displayed all the time (e.g. when spurious mouse events wake up the screen all the time).XSECURELOCK_BURNIN_MITIGATION_DYNAMIC: if set to a non-zero value, auth_x11 will move the prompt while it is being displayed, but stay within the bounds of XSECURELOCK_BURNIN_MITIGATION. The value of this variable is the maximum allowed shift per screen refresh. This mitigates short-term burn-in effects but is probably annoying to most users, and thus disabled by default.XSECURELOCK_COMPOSITE_OBSCURER: create a second full-screen window to obscure window content in case a running compositor unmaps its own window. Helps with some instances of bad compositor behavior (such as compositor crashes/restarts, but also compton has been caught at drawing notification icons above the screen locker when not using the GLX backend), should prevent compositors from unredirecting as it's 1 pixel smaller than the screen from every side, and should otherwise be harmless, so it's enabled by default.XSECURELOCK_DATETIME_FORMAT: the date format to show. Defaults to the locale settings. (see man date for possible formats)XSECURELOCK_DEBUG_ALLOW_LOCKING_IF_INEFFECTIVE: Normally we don't allow locking sessions that are likely not any useful to lock, such as the X11 part of a Wayland session (one could still use Wayland applicatione when locked) or VNC sessions (as it'd only lock the server side session while users will likely think they locked the client, allowing for an easy escape). These checks can be bypassed by setting this variable to 1. Not recommended other than for debugging XSecureLock itself via such connections.XSECURELOCK_DEBUG_WINDOW_INFO: When complaining about another window misbehaving, print not just the window ID but also some info about it. Uses the xwininfo and xprop tools.XSECURELOCK_DIM_ALPHA: Linear-space opacity to fade the screen to.XSECURELOCK_DIM_COLOR: X11 color to fade the screen to.XSECURELOCK_DIM_FPS: Target framerate to attain during the dimming effect of dimmer. Ideally matches the display refresh rate.XSECURELOCK_DIM_MAX_FILL_SIZE: Maximum size (in width or height) to fill at once using an XFillRectangle call. Low values may cause performance loss or noticeable tearing during dimming; high values may cause crashes or hangs with some graphics drivers or a temporarily unresponsive X server.XSECURELOCK_DIM_OVERRIDE_COMPOSITOR_DETECTION: When set to 1, always try to use transparency for dimming; when set to 0, always use a dither pattern. Default is to autodetect whether transparency will likely work.XSECURELOCK_DIM_TIME_MS: Milliseconds to dim for when above xss-lock command line with dimmer is used; also used by wait_nonidle to know when to assume dimming and waiting has finished and exit.XSECURELOCK_DISCARD_FIRST_KEYPRESS: If set to 0, the key pressed to stop the screen saver and spawn the auth child is sent to the auth child (and thus becomes part of the password entry). By default we always discard the key press that started the authentication flow, to prevent users from getting used to type their password on a blank screen (which could be just powered off and have a chat client behind or similar).XSECURELOCK_FONT: X11 or FontConfig font name to use for auth_x11. You can get a list of supported font names by running xlsfonts and fc-list.XSECURELOCK_FORCE_GRAB: When grabbing fails, try stealing the grab from other windows (a value of 2 steals from all descendants of the root window, while a value of 1 only steals from client windows). This works only sometimes and is incompatible with many window managers, so use with care. See the "Forcing Grabs" section below for details.XSECURELOCK_GLOBAL_SAVER: specifies the desired global screen saver module (by default this is a multiplexer that runs XSECURELOCK_SAVER on each screen).XSECURELOCK_IDLE_TIMERS: comma-separated list of idle time counters used by until_nonidle. Typical values are either empty (relies on the X Screen Saver extension instead), "IDLETIME" and "DEVICEIDLETIME <n>" where n is an XInput device index (run xinput to see them). If multiple time counters are specified, the idle time is the minimum of them all. All listed timers must have the same unit.XSECURELOCK_IMAGE_DURATION_SECONDS: how long to show each still image played by saver_mpv. Defaults to 1.XSECURELOCK_KEY_s_COMMAND where s is the name of an X11 keysym (find using xev): a shell command to execute when the specified key is pressed. Useful e.g. for media player control. Beware: be cautious about what you run with this, as it may yield attackers control over your computer.XSECURELOCK_LIST_VIDEOS_COMMAND: shell command to list all video files to potentially play by saver_mpv or saver_mplayer. Defaults to find ~/Videos -type f.XSECURELOCK_NO_COMPOSITE: disables covering the composite overlay window. This switches to a more traditional way of locking, but may allow desktop notifications to be visible on top of the screen lock. Not recommended.XSECURELOCK_NO_PAM_RHOST: do not set PAM_RHOST to localhost, despite recommendation to do so by the Linux-PAM Application Developers' Guide. This may work around bugs in third-party PAM authentication modules. If this solves a problem for you, please report a bug against said PAM module.XSECURELOCK_NO_XRANDR: disables multi monitor support using XRandR.XSECURELOCK_NO_XRANDR15: disables multi monitor support using XRandR 1.5 and fall back to XRandR 1.2. Not recommended.XSECURELOCK_PAM_SERVICE: pam service name. You should have a file with that name in /etc/pam.d.XSECURELOCK_PASSWORD_PROMPT: Choose password prompt mode:asterisks: shows asterisks, like classic password prompts. This is the least secure option because password length is visible. ***_ *******_
cursor: shows a cursor that jumps around on each key press. This is the default. ________|_______________________ ___________________|____________
disco: shows dancers, which dance around on each key press. Requires a font that can handle Unicode line drawing characters, and FontConfig. ┏(･o･)┛ ♪ ┗(･o･)┓ ♪ ┏(･o･)┛ ♪ ┗(･o･)┓ ♪ ┏(･o･)┛ ┗(･o･)┓ ♪ ┏(･o･)┛ ♪ ┏(･o･)┛ ♪ ┏(･o･)┛ ♪ ┏(･o･)┛
emoji: shows an emoji, changing which one on each key press. Requires a font that can handle emoji, and FontConfig. 👍 🎶 💕
emoticon: shows an ascii emoticon, changing which one on each key press. :-O d-X X-\
hidden: completely hides the password, and there's no feedback for keypresses. This would almost be most secure - however as it gives no feedback to input whatsoever, you may not be able to notice accidentally typing to another computer and sending your password to some chatroom.
kaomoji: shows a kaomoji (Japanese emoticon), changing which one on each key press. Requires a Japanese font, and FontConfig. (͡°͜ʖ͡°) (＾ｕ＾) ¯\_(ツ)_/¯
time: shows the current time since the epoch on each keystroke. This may be the most secure mode, as it gives feedback to keystroke based exclusively on public information, and does not carry over any state between keystrokes whatsoever - not even some form of randomness. 1559655410.922329
time_hex: same as time, but in microseconds and hexadecimal. "Because we can". 0x58a7f92bd7359
XSECURELOCK_SAVER: specifies the desired screen saver module.XSECURELOCK_SAVER_RESET_ON_AUTH_CLOSE: specifies whether to reset the saver module when the auth dialog closes. Resetting is done by sending SIGUSR1 to the saver, which may either just terminate, or handle this specifically to do a cheaper reset.XSECURELOCK_SHOW_DATETIME: whether to show local date and time on the login. Disabled by default.XSECURELOCK_SHOW_HOSTNAME: whether to show the hostname on the login screen of auth_x11. Possible values are 0 for not showing the hostname, 1 for showing the short form, and 2 for showing the long form.XSECURELOCK_SHOW_USERNAME: whether to show the username on the login screen of auth_x11.XSECURELOCK_SINGLE_AUTH_WINDOW: whether to show only a single auth window from auth_x11, as opposed to one per screen.XSECURELOCK_SWITCH_USER_COMMAND: shell command to execute when Win-O or Ctrl-Alt-O are pressed (think "_other_ user"). Typical values could be lxdm -c USER_SWITCH, dm-tool switch-to-greeter, gdmflexiserver or kdmctl reserve, depending on your desktop environment.XSECURELOCK_WAIT_TIME_MS: Milliseconds to wait after dimming (and before locking) when above xss-lock command line is used. Should be at least as large as the period time set using "xset s". Also used by wait_nonidle to know when to assume dimming and waiting has finished and exit.XSECURELOCK_XSCREENSAVER_PATH: Location where XScreenSaver hacks are installed for use by saver_xscreensaver.Additionally, command line arguments following a "--" argument will be executed via execvp once locking is successful; this can be used to notify a calling process of successful locking.
The following authentication modules are included:
auth_x11: Authenticates via an authproto module using keyboard input (X11 based; recommended).The authentication module is a separate executable, whose name must start with auth_ and be installed together with the included auth_ modules (default location: /usr/local/libexec/xsecurelock/helpers).
mb* C functions to act on these.$XSCREENSAVER_WINDOW.The following authentication protocol ("authproto") modules are included:
authproto_htpasswd: Authenticates via a htpasswd style file stored in ~/.xsecurelock.pw. To generate this file, run: ( umask 077; htpasswd -cB ~/.xsecurelock.pw "$USER" ) Use this only if you for some reason can't use PAM!authproto_pam: Authenticates via PAM. Use this.authproto_pamtester: Authenticates via PAM using pamtester. Shouldn't be required unless you can't compile authproto_pam. Only supports simple password based conversations.The authentication protocol module is a separate executable, whose name must start with authproto_ and be installed together with the included authproto_ modules (default location: /usr/local/libexec/xsecurelock/helpers).
The following screen saver modules are included:
saver_blank: Simply blanks the screen.saver_mplayer and saver_mpv: Plays a video using mplayer or mpv, respectively. The video to play is selected at random among all files in ~/Videos.saver_multiplex: Watches the display configuration and runs another screen saver module once on each screen; used internally.saver_xscreensaver: Runs an XScreenSaver hack from an existing XScreenSaver setup. NOTE: some screen savers included by this may display arbitrary pictures from your home directory; if you care about this, either run xscreensaver-demo and disable screen savers that may do this, or stay away from this one!The screen saver module is a separate executable, whose name must start with saver_ and be installed together with the included auth_ modules (default location: /usr/local/libexec/xsecurelock/helpers).
$XSCREENSAVER_WINDOW.XSECURELOCK_SAVER_RESET_ON_AUTH_CLOSE.In order to achieve maximum possible security against screen lock bypass exploits, the following measures are taken:
sh -c "xsecurelock ... || kill -9 -1" :)xss-lock, this could leave a workstation open for days. Above ... || kill -9 -1 workaround would mitigate this issue too by simply killing the entire session if locking it fails.XQueryKeymap).XQueryPointer)./dev/input), including other input devices than keyboard and mouse, such as gamepads or joysticks.Most these issues are inherent with X11 and can only really be fixed by migrating to an alternative such as Wayland; some of the issues (in particular the gamepad input issue) will probably persist even with Wayland.
As a workaround to the issue of another window already holding a grab, we offer an XSECURELOCK_FORCE_GRAB option.
This adds a last measure attempt to force grabbing by iterating through all subwindows of the root window, unmapping them (which closes down their grabs), then taking the grab and mapping them again.
This has the following known issues:
OverrideRedirect to gain fullscreen mode), the window will become unresponsive, as your actions will be interpreted by another window - which you can't see - instead. Alt-Tabbing around may often work around this.nouveau graphics driver, using a compositor that uses the Composite Overlay Window (e.g. compton with the flags --backend glx --paint-on-overlay) or passing XSECURELOCK_NO_COMPOSITE=1 to XSecureLock (which however may make notifications appear on top of the screen lock).metacity (a GNOME component) because it draws on the Compositor Overlay Window with IncludeInferiors set (i.e. it explicitly requests to draw on top of programs like XSecureLock). It likely does this because the same is necessary when drawing on top of the root window, which it had done in the past but no longer does. Workarounds include disabling its compositor with gsettings set org.gnome.metacity compositing-manager false or passing XSECURELOCK_NO_COMPOSITE=1 to XSecureLock.compton --backend glx --paint-on-overlay. In worst case you can turn off our workaround for transparent windows by setting XSECURELOCK_NO_COMPOSITE=1.The code is released under the Apache 2.0 license. See the LICENSE file for more details.
This project is not an official Google project. It is not supported by Google and Google specifically disclaims all warranties as to its quality, merchantability, or fitness for a particular purpose.
1.8.14