Session lock

Secure session locking with arbitrary graphics

This protocol allows for a privileged Wayland client to lock the session and display arbitrary graphics while the session is locked.

The compositor may choose to restrict this protocol to a special client launched by the compositor itself or expose it to all privileged clients, this is compositor policy.

The client is responsible for performing authentication and informing the compositor when the session should be unlocked. If the client dies while the session is locked the session remains locked, possibly permanently depending on compositor policy.

The key words "must", "must not", "required", "shall", "shall not", "should", "should not", "recommended", "may", and "optional" in this document are to be interpreted as described in IETF RFC 2119.

Warning! The protocol described in this file is currently in the testing phase. Backward compatible changes may be added together with the corresponding interface version bump. Backward incompatible changes can only be done by creating a new major version of the extension.

Used to lock the session

This interface is used to request that the session be locked.

destroy()
Destroy the session lock manager object

This informs the compositor that the session lock manager object will no longer be used. Existing objects created through this interface remain valid.

lock(id: new_id<ext_session_lock_v1>)
Argument
Type
Description
idnew_id<ext_session_lock_v1>
Attempt to lock the session

This request creates a session lock and asks the compositor to lock the session. The compositor will send either the ext_session_lock_v1.locked or ext_session_lock_v1.finished event on the created object in response to this request.


Manage lock state and create lock surfaces

In response to the creation of this object the compositor must send either the locked or finished event.

The locked event indicates that the session is locked. This means that the compositor must stop rendering and providing input to normal clients. Instead the compositor must blank all outputs with an opaque color such that their normal content is fully hidden.

The only surfaces that should be rendered while the session is locked are the lock surfaces created through this interface and optionally, at the compositor's discretion, special privileged surfaces such as input methods or portions of desktop shell UIs.

The locked event must not be sent until a new "locked" frame (either from a session lock surface or the compositor blanking the output) has been presented on all outputs and no security sensitive normal/unlocked content is possibly visible.

The finished event should be sent immediately on creation of this object if the compositor decides that the locked event will not be sent.

The compositor may wait for the client to create and render session lock surfaces before sending the locked event to avoid displaying intermediate blank frames. However, it must impose a reasonable time limit if waiting and send the locked event as soon as the hard requirements described above can be met if the time limit expires. Clients should immediately create lock surfaces for all outputs on creation of this object to make this possible.

This behavior of the locked event is required in order to prevent possible race conditions with clients that wish to suspend the system or similar after locking the session. Without these semantics, clients triggering a suspend after receiving the locked event would race with the first "locked" frame being presented and normal/unlocked frames might be briefly visible as the system is resumed if the suspend operation wins the race.

If the client dies while the session is locked, the compositor must not unlock the session in response. It is acceptable for the session to be permanently locked if this happens. The compositor may choose to continue to display the lock surfaces the client had mapped before it died or alternatively fall back to a solid color, this is compositor policy.

Compositors may also allow a secure way to recover the session, the details of this are compositor policy. Compositors may allow a new client to create a ext_session_lock_v1 object and take responsibility for unlocking the session, they may even start a new lock client instance automatically.

destroy()
Destroy the session lock

This informs the compositor that the lock object will no longer be used. Existing objects created through this interface remain valid.

After this request is made, lock surfaces created through this object should be destroyed by the client as they will no longer be used by the compositor.

It is a protocol error to make this request if the locked event was sent, the unlock_and_destroy request must be used instead.

get_lock_surface(id: new_id<ext_session_lock_surface_v1>, surface: object<wl_surface>, output: object<wl_output>)
Argument
Type
Description
idnew_id<ext_session_lock_surface_v1>
surfaceobject<wl_surface>
outputobject<wl_output>
Create a lock surface for a given output

The client is expected to create lock surfaces for all outputs currently present and any new outputs as they are advertised. These won't be displayed by the compositor unless the lock is successful and the locked event is sent.

Providing a wl_surface which already has a role or already has a buffer attached or committed is a protocol error, as is attaching/committing a buffer before the first ext_session_lock_surface_v1.configure event.

Attempting to create more than one lock surface for a given output is a duplicate_output protocol error.

unlock_and_destroy()
Unlock the session, destroying the object

This request indicates that the session should be unlocked, for example because the user has entered their password and it has been verified by the client.

This request also informs the compositor that the lock object will no longer be used and should be destroyed. Existing objects created through this interface remain valid.

After this request is made, lock surfaces created through this object should be destroyed by the client as they will no longer be used by the compositor.

It is a protocol error to make this request if the locked event has not been sent. In that case, the lock object must be destroyed using the destroy request.

Note that a correct client that wishes to exit directly after unlocking the session must use the wl_display.sync request to ensure the server receives and processes the unlock_and_destroy request. Otherwise there is no guarantee that the server has unlocked the session due to the asynchronous nature of the Wayland protocol. For example, the server might terminate the client with a protocol error before it processes the unlock_and_destroy request.

locked()
Session successfully locked

This client is now responsible for displaying graphics while the session is locked and deciding when to unlock the session.

The locked event must not be sent until a new "locked" frame has been presented on all outputs and no security sensitive normal/unlocked content is possibly visible.

If this event is sent, making the destroy request is a protocol error, the lock object must be destroyed using the unlock_and_destroy request.

finished()
The session lock object should be destroyed

The compositor has decided that the session lock should be destroyed as it will no longer be used by the compositor. Exactly when this event is sent is compositor policy, but it must never be sent more than once for a given session lock object.

This might be sent because there is already another ext_session_lock_v1 object held by a client, or the compositor has decided to deny the request to lock the session for some other reason. This might also be sent because the compositor implements some alternative, secure way to authenticate and unlock the session.

The finished event should be sent immediately on creation of this object if the compositor decides that the locked event will not be sent.

If the locked event is sent on creation of this object the finished event may still be sent at some later time in this object's lifetime. This is compositor policy.

Upon receiving this event, the client should make either the destroy request or the unlock_and_destroy request, depending on whether or not the locked event was received on this object.

Argument
Value
Description
invalid_destroy0
attempted to destroy session lock while locked
invalid_unlock1
unlock requested but locked event was never sent
role2
given wl_surface already has a role
duplicate_output3
given output already has a lock surface
already_constructed4
given wl_surface has a buffer attached or committed

A surface displayed while the session is locked

The client may use lock surfaces to display a screensaver, render a dialog to enter a password and unlock the session, or however else it sees fit.

On binding this interface the compositor will immediately send the first configure event. After making the ack_configure request in response to this event the client should attach and commit the first buffer. Committing the surface before acking the first configure is a protocol error. Committing the surface with a null buffer at any time is a protocol error.

The compositor is free to handle keyboard/pointer focus for lock surfaces however it chooses. A reasonable way to do this would be to give the first lock surface created keyboard focus and change keyboard focus if the user clicks on other surfaces.

destroy()
Destroy the lock surface object

This informs the compositor that the lock surface object will no longer be used.

It is recommended for a lock client to destroy lock surfaces if their corresponding wl_output global is removed.

If a lock surface on an active output is destroyed before the ext_session_lock_v1.unlock_and_destroy event is sent, the compositor must fall back to rendering a solid color.

ack_configure(serial: uint)
Argument
Type
Description
serialuint
serial from the configure event
Ack a configure event

When a configure event is received, if a client commits the surface in response to the configure event, then the client must make an ack_configure request sometime before the commit request, passing along the serial of the configure event.

If the client receives multiple configure events before it can respond to one, it only has to ack the last configure event.

A client is not required to commit immediately after sending an ack_configure request - it may even ack_configure several times before its next surface commit.

A client may send multiple ack_configure requests before committing, but only the last request sent before a commit indicates which configure event the client really is responding to.

Sending an ack_configure request consumes the configure event referenced by the given serial, as well as all older configure events sent on this object.

It is a protocol error to issue multiple ack_configure requests referencing the same configure event or to issue an ack_configure request referencing a configure event older than the last configure event acked for a given lock surface.

configure(serial: uint, width: uint, height: uint)
Argument
Type
Description
serialuint
serial for use in ack_configure
widthuint
heightuint
The client should resize its surface

This event is sent once on binding the interface and may be sent again at the compositor's discretion, for example if output geometry changes.

The width and height are in surface-local coordinates and are exact requirements. Failing to match these surface dimensions in the next commit after acking a configure is a protocol error.

Argument
Value
Description
commit_before_first_ack0
surface committed before first ack_configure request
null_buffer1
surface committed with a null buffer
dimensions_mismatch2
failed to match ack'd width/height
invalid_serial3
serial provided in ack_configure is invalid

Compositor Support

MutterMutter
8/31/2023
KWinKWin
11/13/2023
SwaySway
1/7/2023
WestonWeston
9/27/2023
MirMir
7/22/2023
gamescopegamescope
12/14/2023
ext_session_lock_manager_v1
x
x
1
x
1
x

Copyright 2021 Isaac Freund

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