CVE-2026-99169futex: Fix mm reuse handling for FUT_OFF_MMSHARED

Official description

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.)

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/096b5d4b80d19b1f7bf8e63fae0d0a32dbb6e1a2
• https://git.kernel.org/stable/c/a7aa4ce1b56a688fe4da75430ec7bf9fe3311807
• https://git.kernel.org/stable/c/f470b76584b5e32d9f9436ef78fb899914116d75
• https://git.kernel.org/stable/c/0c133ed51700036796318f038dde813976bf1227
• https://git.kernel.org/stable/c/16cc0fee39dffd9994b7bea676a886ed52206754
• https://git.kernel.org/stable/c/c17cc2027773e8e4913c5ab0fe3a489b1ed5bf81
• https://git.kernel.org/stable/c/2855ddc6844f527e375e78afb55ec2a5182f23b3
• https://git.kernel.org/stable/c/3267512ad1c2cc0c7768c5b014dc2cceb398a801