UBUNTU-CVE-2026-80778

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UBUNTU-CVE-2026-80778

Summary:

Details: 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 ]

References: https://ubuntu.com/security/CVE-2026-80778, https://www.cve.org/CVERecord?id=CVE-2026-80778, https://git.kernel.org/linus/59b3732f95dda1fbd2234514d35f4fb6b5bb6d85