futex: Fix mm reuse handling for FUT_OFF_MMSHARED

Summary

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.)

Timeline

1. Oct 28, 2026, 10:35 AM UTCCVE published
2. Oct 28, 2026, 10:41 AM UTCFirst seen by cve.now
3. Oct 30, 2026, 12:42 PM UTCRecord last updated

Affected versions

• Linux Linux

  Version range not reported

• Linux Linux

  5.7

• KernelLinux

  From 5.7.0 · fixed in 6.18.59; From 6.19.0 · fixed in 7.2.13

References 8