CVE-2026-64509

rust: block: fix GenDisk cleanup paths

In the Linux kernel, the following vulnerability has been resolved: rust: block: fix GenDisk cleanup paths GenDiskBuilder::build() still has fallible work after __blk_mq_alloc_disk(), but its error path only recovers the foreign queue data. That leaks the temporary gendisk and request_queue until later teardown. If the caller moved the last Arc<TagSet<T>> into build(), the leaked queue can retain blk-mq state after the tag set is dropped. Fix the pre-registration failure path by dropping the temporary gendisk reference with put_disk() before recovering queue_data, so disk_release() can tear down the owned queue. Also pair GenDisk::drop() with put_disk() after del_gendisk(). Once a Rust GenDisk has been added with device_add_disk(), del_gendisk() only unregisters it; the final gendisk reference still has to be dropped to complete the release path.