rust: drm: ioctl: fix unbounded lifetimes in ioctl handler arguments

References to dev, data, and file in the declare_drm_ioctls! macro are
created via unsafe pointer dereferences, producing unbounded lifetimes.
If an ioctl handler explicitly annotates its parameters with 'static,
the compiler accepts this, allowing the handler to stash references that
outlive the ioctl call.

Fix this by adding a higher-ranked function pointer coercion that
enforces the handler accepts universally quantified lifetimes:

  let _: for<'a> fn(&'a _, &'a mut _, &'a _) -> _ = $func;

Since the handler must be coercible to a function pointer accepting any
lifetime 'a, it can no longer demand 'static on any parameter.

Cc: stable@vger.kernel.org
Fixes: 9a69570682 ("rust: drm: ioctl: Add DRM ioctl abstraction")
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/all/20260620011346.A47D01F000E9@smtp.kernel.org/
Suggested-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Tested-by: Deborah Brouwer <deborah.brouwer@collabora.com>
Link: https://patch.msgid.link/20260628145406.2107056-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

rust/kernel/drm/ioctl.rs

@@ -135,6 +135,12 @@ macro_rules! declare_drm_ioctls {
                             // dev/file match the current driver these ioctls are being declared
                             // for, and it's not clear how to enforce this within the type system.
                             let dev = $crate::drm::device::Device::from_raw(raw_dev);
+
+                            // Enforce that the handler accepts higher-ranked
+                            // lifetimes, preventing it from requiring 'static
+                            // references that could escape this scope.
+                            let _: for<'a> fn(&'a _, &'a mut _, &'a _) -> _ = $func;
+
                             // SAFETY: The ioctl argument has size `_IOC_SIZE(cmd)`, which we
                             // asserted above matches the size of this type, and all bit patterns of
                             // UAPI structs must be valid.