CVE-2026-52930

In the Linux kernel, the following vulnerability has been resolved:

ipc/shm: serialize orphan cleanup with shm_nattch updates

shm_destroy_orphaned() walks the shm idr under shm_ids(ns).rwsem, but that
does not serialize all fields tested by shm_may_destroy().  In particular,
shm_nattch is updated while holding shm_perm.lock, and attach paths can do
that without holding the rwsem.

Do not decide that an orphaned segment is unused before taking the object
lock.  Move the shm_may_destroy() check under shm_perm.lock, matching the
other destroy paths, and unlock the segment when it no longer qualifies
for removal.