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Mitigate UAF crashes due to iteration over freed wl_resources

Thomas Lukaszewicz requested to merge tluk/wayland:resource-destruction-iteration into main

Currently it is possible to iterate over client-owned resources during client destruction that have had their associated memory released.

This can occur when client code calls wl_client_destroy(). The following sequence illustrates how this may occur.

  1. The server initiates destruction of the connected client via call to wl_client_destroy().

  2. Resource destroy listeners / destructors are invoked and resource memory is freed one resource at a time [1].

  3. If a listener / destructor for a resource results in a call to wl_client_for_each_resource(), the iteration will proceed over resources that have been previously freed in step 2, resulting in UAFs / crashes.

The issue is that resources remain in the client's object map even after they have had their memory freed, and are removed from the map only after each individual resource has had its memory released.

This patch corrects this by ensuring resource destruction first invokes listeners / destructors and then removing them from the client's object map before releasing the associated memory.

[1] https://gitlab.freedesktop.org/wayland/wayland/-/blob/main/src/wayland-server.c?ref_type=heads#L928

Signed-off-by: Thomas Lukaszewicz thomaslukaszewicz@gmail.com

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