Advisory [CVE-2026-64509] 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> 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.

This vulnerability occurs in the `GenDisk` cleanup paths, where temporary disk and request queue resources may not be properly released during error handling or after unregistration. This can lead to a resource leak, potentially causing system instability or a denial of service (DoS) due to resource exhaustion.

Red Hat severity: not rated. Weakness: CWE-772.

Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9 as not affected.