Bug 2562711 (CVE-2026-99169)

Summary: CVE-2026-99169 kernel: futex: Fix mm reuse handling for FUT_OFF_MMSHARED
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
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's futex (fast userspace mutex) subsystem. A local user can cause a Denial of Service (DoS) by exploiting improper handling of shared waiters when memory is reused. By requeuing synchronization waiters across different memory contexts, a waiter tied to freed memory can intercept wakeups intended for newly allocated memory at the same address, causing threads to deadlock or hang indefinitely.
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Description OSIDB Bzimport 2026-10-28 10:55:04 UTC 
In the Linux kernel, the following vulnerability has been resolved:

futex: Fix mm reuse handling for FUT_OFF_MMSHARED

A FUT_OFF_MMSHARED futex is a shared futex that refers to an MM.
It is possible for a process to wait on a shared futex with a different MM
because a FUT_OFF_INODE waiter can be requeued onto a FUT_OFF_MMSHARED
futex by another process.
This can cause FUT_OFF_MMSHARED waiters on a freed MM to consume
wakeups intended for a newly allocated MM at the same address.

Fix it by keying FUT_OFF_MMSHARED using a unique 64-bit per-MM ID.
Leave private futexes as before to avoid influencing the performance of the
hotpath.

(Multi-threaded processes typically implicitly use FUT_OFF_MMSHARED by
setting clear_child_tid such that it points into anonymous memory, which
causes mm_release() in a multi-threaded mm to perform FUTEX_WAKE.)