GHSA-M59R-FCC7-PM78
Vulnerability from github – Published: 2026-09-16 12:30 – Updated: 2026-09-16 15:31In the Linux kernel, the following vulnerability has been resolved:
futex: Prevent rcuwait use-after-free during requeue PI
On PREEMPT_RT, FUTEX_CMP_REQUEUE_PI can trigger a KASAN report (slab-out-of-bounds) in futex_requeue_pi_complete() invocation of rcuwait_wake_up().
The futex_q used by futex_wait_requeue_pi() is allocated on the waiter's stack. An early wakeup can race with a PI requeue as follows:
waiter requeue task
------ ------------
futex_wait_requeue_pi() futex_do_wait() schedule() futex_requeue futex_proxy_trylock_atomic() futex_requeue_pi_prepare() Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_IN_PROGRESS * timeout/ signal wakes waiter * futex_requeue_pi_wakeup_sync() Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_WAIT requeue_pi_wake_futex futex_requeue_pi_complete() cmpxchg Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_LOCKED rcuwait_wait_event() if (atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT) break / no schedule() /
/ q.pi_state->owner == current / futex_private_hash_put() / return from syscall / rcuwait_wake_up(&q->requeue_wait) / q is gone /
futex_requeue_pi_complete() publishes Q_REQUEUE_PI_LOCKED before calling rcuwait_wake_up(). The waiter observes this state in rcuwait_wait_event() before invoking schedule() in rcuwait_wait_event(). Here, the waiter is free leave the syscall before requeue task can complete the wake.
To address this race skip rcuwait_wake_up() in the Q_REQUEUE_PI_LOCKED case. This state is only published by requeue_pi_wake_futex(), which saves q->task before futex_requeue_pi_complete() and wakes the waiter via wake_up_state().
This wake is intended to wake the waiter from its futex_do_wait() sleep. If the waiter is still sleeping there, it can not get into the Q_REQUEUE_PI_WAIT state (and require this removed wake). Should the waiter be woken up from futex_do_wait() by other means (as in this example) and sleep in futex_requeue_pi_wakeup_sync() then the wake_up_state() from requeue_pi_wake_futex() will wake it, too. Should the waiter task terminate before wake_up_state() had a chance to wake the task then the task pointer does not become invalid because the futex_hash_bucket::lock is held and the task pointer is RCU protected.
[bigeasy: Updated comment and commit message]
{
"affected": [],
"aliases": [
"CVE-2026-90003"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-16T11:17:12Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nfutex: Prevent rcuwait use-after-free during requeue PI\n\nOn PREEMPT_RT, FUTEX_CMP_REQUEUE_PI can trigger a KASAN report\n(slab-out-of-bounds) in futex_requeue_pi_complete() invocation of\nrcuwait_wake_up().\n\nThe futex_q used by futex_wait_requeue_pi() is allocated on the waiter\u0027s\nstack. An early wakeup can race with a PI requeue as follows:\n\n waiter requeue task\n ------ ------------\nfutex_wait_requeue_pi()\n futex_do_wait()\n schedule()\n futex_requeue\n futex_proxy_trylock_atomic()\n futex_requeue_pi_prepare()\n Q_REQUEUE_PI_NONE -\u003e Q_REQUEUE_PI_IN_PROGRESS\n* timeout/ signal wakes waiter *\n futex_requeue_pi_wakeup_sync()\n Q_REQUEUE_PI_IN_PROGRESS -\u003e Q_REQUEUE_PI_WAIT\n requeue_pi_wake_futex\n futex_requeue_pi_complete()\n cmpxchg Q_REQUEUE_PI_WAIT -\u003e Q_REQUEUE_PI_LOCKED\n rcuwait_wait_event()\n if (atomic_read(\u0026q-\u003erequeue_state) != Q_REQUEUE_PI_WAIT)\n break /* no schedule() */\n\n /* q.pi_state-\u003eowner == current */\n futex_private_hash_put()\n /* return from syscall */\n rcuwait_wake_up(\u0026q-\u003erequeue_wait)\n /* q is gone */\n\nfutex_requeue_pi_complete() publishes Q_REQUEUE_PI_LOCKED before\ncalling rcuwait_wake_up(). The waiter observes this state in\nrcuwait_wait_event() before invoking schedule() in rcuwait_wait_event().\nHere, the waiter is free leave the syscall before requeue task can\ncomplete the wake.\n\nTo address this race skip rcuwait_wake_up() in the Q_REQUEUE_PI_LOCKED\ncase.\nThis state is only published by requeue_pi_wake_futex(), which saves\nq-\u003etask before futex_requeue_pi_complete() and wakes the waiter via\nwake_up_state().\n\nThis wake is intended to wake the waiter from its futex_do_wait() sleep.\nIf the waiter is still sleeping there, it can not get into the\nQ_REQUEUE_PI_WAIT state (and require this removed wake).\nShould the waiter be woken up from futex_do_wait() by other means (as in\nthis example) and sleep in futex_requeue_pi_wakeup_sync() then the\nwake_up_state() from requeue_pi_wake_futex() will wake it, too.\nShould the waiter task terminate before wake_up_state() had a chance to\nwake the task then the task pointer does not become invalid because the\nfutex_hash_bucket::lock is held and the task pointer is RCU protected.\n\n[bigeasy: Updated comment and commit message]",
"id": "GHSA-m59r-fcc7-pm78",
"modified": "2026-09-16T15:31:06Z",
"published": "2026-09-16T12:30:44Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90003"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/220ee9e04ca3b7f014c000264aa6c884f036c86e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/244f301759fd34b1dd0b4192ce44f8ef224e027d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7d1559126d86be6e4f6a85663dfbfe85caa47e37"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/81aadbd09bf1dcd3238212f336ba699503557ae8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a3b8d46fe401cba3a5c46dea610e6eb3dc15370e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e4a4ccfa470f910b747b3ee8d18670ed8ac8a236"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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