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.)
Analysis
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Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||
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| Linux | Linux | unaffected |
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| Linux | Linux | affected |
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Wed, 28 Oct 2026 13:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-416 |
Wed, 28 Oct 2026 10:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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.) | |
| Title | futex: Fix mm reuse handling for FUT_OFF_MMSHARED | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-28T10:35:20.170Z
Reserved: 2026-09-25T10:25:14.398Z
Link: CVE-2026-99169
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-28T11:17:37.403
Modified: 2026-10-28T11:17:37.403
Link: CVE-2026-99169
Redhat
No data.
OpenCVE Enrichment
Updated: 2026-10-28T13:00:15Z
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CWE-416
Use After Free