CVE-2026-80778

/// Technical description

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

futex/pi: Reject cross-mm private futex owners

A private futex key borrows the waiter's mm without taking an mm_users

reference. Nevertheless, attach_to_pi_owner() currently accepts an owner

from a different address space and copies the private key into the owner's

PI state.

When that owner exits, exit_pi_state_list() uses the saved key to find the

hash bucket and acquires a reference to the waiter's private hash. If the

last user of the waiter's mm exits concurrently, futex_hash_free() frees

the hash while the owner still uses its bucket and reference.

Prevent this by validating in attach_to_pi_owner() that, for private

futexes, the owner mm and waiter mm are the same. Perform the check with

the owner's pi_lock held and after validating owner::futex::state to

serialize against a concurrent PI-state exit cleanup.

[ tglx: Amended comment ]

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References