FKIE_CVE-2026-31555

Vulnerability from fkie_nvd - Published: 2026-04-24 15:16 - Updated: 2026-04-24 17:51
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: futex: Clear stale exiting pointer in futex_lock_pi() retry path Fuzzying/stressing futexes triggered: WARNING: kernel/futex/core.c:825 at wait_for_owner_exiting+0x7a/0x80, CPU#11: futex_lock_pi_s/524 When futex_lock_pi_atomic() sees the owner is exiting, it returns -EBUSY and stores a refcounted task pointer in 'exiting'. After wait_for_owner_exiting() consumes that reference, the local pointer is never reset to nil. Upon a retry, if futex_lock_pi_atomic() returns a different error, the bogus pointer is passed to wait_for_owner_exiting(). CPU0 CPU1 CPU2 futex_lock_pi(uaddr) // acquires the PI futex exit() futex_cleanup_begin() futex_state = EXITING; futex_lock_pi(uaddr) futex_lock_pi_atomic() attach_to_pi_owner() // observes EXITING *exiting = owner; // takes ref return -EBUSY wait_for_owner_exiting(-EBUSY, owner) put_task_struct(); // drops ref // exiting still points to owner goto retry; futex_lock_pi_atomic() lock_pi_update_atomic() cmpxchg(uaddr) *uaddr ^= WAITERS // whatever // value changed return -EAGAIN; wait_for_owner_exiting(-EAGAIN, exiting) // stale WARN_ON_ONCE(exiting) Fix this by resetting upon retry, essentially aligning it with requeue_pi.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/210d36d892de5195e6766c45519dfb1e65f3eb83
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5e8e06bf8909e79b4acd950cf578cfc2f10bbefa
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/71112e62807d1925dc3ae6188b11f8cfc85aec23
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7475dfad10a05a5bfadebf5f2499bd61b19ed293
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/92e47ad03e03dbb5515bdf06444bf6b1e147310d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/de7c0c04ad868f2cee6671b11c0a6d20421af1da
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e7824ec168d2ac883a213cd1f4d6cc0816002a85
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfutex: Clear stale exiting pointer in futex_lock_pi() retry path\n\nFuzzying/stressing futexes triggered:\n\n    WARNING: kernel/futex/core.c:825 at wait_for_owner_exiting+0x7a/0x80, CPU#11: futex_lock_pi_s/524\n\nWhen futex_lock_pi_atomic() sees the owner is exiting, it returns -EBUSY\nand stores a refcounted task pointer in \u0027exiting\u0027.\n\nAfter wait_for_owner_exiting() consumes that reference, the local pointer\nis never reset to nil. Upon a retry, if futex_lock_pi_atomic() returns a\ndifferent error, the bogus pointer is passed to wait_for_owner_exiting().\n\n  CPU0\t\t\t     CPU1\t\t       CPU2\n  futex_lock_pi(uaddr)\n  // acquires the PI futex\n  exit()\n    futex_cleanup_begin()\n      futex_state = EXITING;\n\t\t\t     futex_lock_pi(uaddr)\n\t\t\t       futex_lock_pi_atomic()\n\t\t\t\t attach_to_pi_owner()\n\t\t\t\t   // observes EXITING\n\t\t\t\t   *exiting = owner;  // takes ref\n\t\t\t\t   return -EBUSY\n\t\t\t       wait_for_owner_exiting(-EBUSY, owner)\n\t\t\t\t put_task_struct();   // drops ref\n\t\t\t       // exiting still points to owner\n\t\t\t       goto retry;\n\t\t\t       futex_lock_pi_atomic()\n\t\t\t\t lock_pi_update_atomic()\n\t\t\t\t   cmpxchg(uaddr)\n\t\t\t\t\t*uaddr ^= WAITERS // whatever\n\t\t\t\t   // value changed\n\t\t\t\t return -EAGAIN;\n\t\t\t       wait_for_owner_exiting(-EAGAIN, exiting) // stale\n\t\t\t\t WARN_ON_ONCE(exiting)\n\nFix this by resetting upon retry, essentially aligning it with requeue_pi."
    }
  ],
  "id": "CVE-2026-31555",
  "lastModified": "2026-04-24T17:51:40.810",
  "metrics": {},
  "published": "2026-04-24T15:16:29.837",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/210d36d892de5195e6766c45519dfb1e65f3eb83"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/5e8e06bf8909e79b4acd950cf578cfc2f10bbefa"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/71112e62807d1925dc3ae6188b11f8cfc85aec23"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/7475dfad10a05a5bfadebf5f2499bd61b19ed293"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/92e47ad03e03dbb5515bdf06444bf6b1e147310d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/de7c0c04ad868f2cee6671b11c0a6d20421af1da"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e7824ec168d2ac883a213cd1f4d6cc0816002a85"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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