CVE-2026-58094: TOCTOU race in POSIX shared memory large page configuration
The FIOSSHMLPGCNF ioctl(2) operation configures the page size for a largepage shared memory object. This is intended to be used immediately after creating the object, before any memory is allocated for the object. The handler checked whether a page size had already been configured without holding the rangelock. Two concurrent callers could both observe an unconfigured object and set conflicting page sizes, leaving the object in an inconsistent state.
An unprivileged local user can exploit this race to escalate privileges.
Event History
Frequently Asked Questions
Who is exposed to this issue?
Systems where unprivileged local users can create and concurrently configure largepage POSIX shared memory objects are exposed. The described impact is local privilege escalation, so remote access is not indicated by the available information.
What does an attacker need to exploit the flaw?
An attacker needs local unprivileged access and must race two concurrent FIOSSHMLPGCNF ioctl(2) calls against the same newly created largepage shared memory object before memory is allocated for it. The race relies on both callers observing that no page size has yet been configured.
How can I tell whether an object has entered the vulnerable inconsistent state?
The available information states that conflicting page sizes can leave the object in an inconsistent state, but it does not provide a detection method, affected version list, or observable indicators.