Bug 2528594 (CVE-2026-80778)

Summary: CVE-2026-80778 kernel: futex/pi: Reject cross-mm private futex owners
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel. A race condition exists in the futex/pi (Fast Userspace Mutexes / Priority Inheritance) subsystem. When a private futex key borrows a waiter's memory management (mm) structure without proper referencing, the attach_to_pi_owner() function can accept an owner from a different address space. This can lead to a situation where the futex hash is freed while still being used by an owner, potentially causing a use-after-free vulnerability. A local attacker could exploit this to cause a denial of service or system instability.
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Description OSIDB Bzimport 2026-09-04 15:37:35 UTC 
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 ]
Comment 1 gkamathe 2026-09-08 10:38:47 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-80778.mbox