Re: [PATCH] rust_binder: do not query current thread for all ioctls

[Alice Ryhl]

On Mon, Jul 27, 2026 at 2:29 PM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
>
> The get_current_thread() method is currently called for every ioctl to
> ensure that a Thread struct exists for the thread calling into the
> driver. However, not all ioctls require a Thread object, so this means
> we are unnecessarily creating these objects in cases where we don't need
> to. If said thread does not invoke BINDER_THREAD_EXIT on exit, Binder's
> Thread struct stays around until the fd is closed. For long-lived
> processes the Thread object is effectively leaked.
>
> Furthermore, when the BINDER_GET_NODE_DEBUG_INFO ioctl is invoked by
> libmemunreachable to ensure that objects reachable only through the
> Binder driver are not considered leaked, this is done from a fork of the
> process owning the fd, which means that it fails the group_leader check
> inside get_current_thread(). This results in EINVAL errors for this
> ioctl, causing libmemunreachable to report a false positive memory leak.
>
> Thus, do not invoke get_current_thread() for ioctls that do not require
> it.
>
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>

Oh I forgot to mark this as Fixes

Cc: stable@xxxxxxxxxxxxxxx
Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver")

Greg let me know if you need a version for this.