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CVE-2022-49783

Estado: AnalizadaMedia (5.5)—

In the Linux kernel, the following vulnerability has been resolved:

x86/fpu: Drop fpregs lock before inheriting FPU permissions

Mike Galbraith reported the following against an old fork of preempt-rt but the same issue also applies to the current preempt-rt tree.

Mike says:

Mike's assessment looks correct. fpregs_lock on a PREEMPT_RT kernel disables preemption so calling spin_lock_irq() in fpu_inherit_perms() is unsafe. This problem exists since commit

Even though the original bug report should not have enabled the paths at all, the bug still exists.

fpregs_lock is necessary when editing the FPU registers or a task's FP state but it is not necessary for fpu_inherit_perms().

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The only write of any FP state in fpu_inherit_perms() is for the new child which is not running yet and cannot context switch or be borrowed by a kernel thread yet. Hence, fpregs_lock is not protecting anything in the new child until clone() completes and can be dropped earlier. The siglock still needs to be acquired by fpu_inherit_perms() as the read of the parent's permissions has to be serialised.

Detalles técnicos trazas, registros y código del informe original
   BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
   in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd
   preempt_count: 1, expected: 0
   RCU nest depth: 0, expected: 0
   Preemption disabled at:
   fpu_clone
   CPU: 6 PID: 1 Comm: systemd Tainted: G            E       (unreleased)
   Call Trace:
    <TASK>
    dump_stack_lvl
    ? fpu_clone
    __might_resched
    rt_spin_lock
    fpu_clone
    ? copy_thread
    ? copy_process
    ? shmem_alloc_inode
    ? kmem_cache_alloc
    ? kernel_clone
    ? __do_sys_clone
    ? do_syscall_64
    ? __x64_sys_rt_sigprocmask
    ? syscall_exit_to_user_mode
    ? do_syscall_64
    ? syscall_exit_to_user_mode
    ? do_syscall_64
    ? syscall_exit_to_user_mode
    ? do_syscall_64
    ? exc_page_fault
    ? entry_SYSCALL_64_after_hwframe
    </TASK>

  The splat comes from fpu_inherit_perms() being called under fpregs_lock(),
  and us reaching the spin_lock_irq() therein due to fpu_state_size_dynamic()
  returning true despite static key __fpu_state_size_dynamic having never
  been enabled.

  9e798e9aa14c ("x86/fpu: Prepare fpu_clone() for dynamically enabled features").

  [ bp: Cleanup splat. ]

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

Mostrar
{
  "id": "CVE-2022-49783",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
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        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
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          "version": "3.1",
          "baseScore": 5.5,
          "attackVector": "LOCAL",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "NONE"
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      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/fpu: Drop fpregs lock before inheriting FPU permissions\n\nMike Galbraith reported the following against an old fork of preempt-rt\nbut the same issue also applies to the current preempt-rt tree.\n\n   BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46\n   in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd\n   preempt_count: 1, expected: 0\n   RCU nest depth: 0, expected: 0\n   Preemption disabled at:\n   fpu_clone\n   CPU: 6 PID: 1 Comm: systemd Tainted: G            E       (unreleased)\n   Call Trace:\n    <TASK>\n    dump_stack_lvl\n    ? fpu_clone\n    __might_resched\n    rt_spin_lock\n    fpu_clone\n    ? copy_thread\n    ? copy_process\n    ? shmem_alloc_inode\n    ? kmem_cache_alloc\n    ? kernel_clone\n    ? __do_sys_clone\n    ? do_syscall_64\n    ? __x64_sys_rt_sigprocmask\n    ? syscall_exit_to_user_mode\n    ? do_syscall_64\n    ? syscall_exit_to_user_mode\n    ? do_syscall_64\n    ? syscall_exit_to_user_mode\n    ? do_syscall_64\n    ? exc_page_fault\n    ? entry_SYSCALL_64_after_hwframe\n    </TASK>\n\nMike says:\n\n  The splat comes from fpu_inherit_perms() being called under fpregs_lock(),\n  and us reaching the spin_lock_irq() therein due to fpu_state_size_dynamic()\n  returning true despite static key __fpu_state_size_dynamic having never\n  been enabled.\n\nMike's assessment looks correct. fpregs_lock on a PREEMPT_RT kernel disables\npreemption so calling spin_lock_irq() in fpu_inherit_perms() is unsafe. This\nproblem exists since commit\n\n  9e798e9aa14c (\"x86/fpu: Prepare fpu_clone() for dynamically enabled features\").\n\nEven though the original bug report should not have enabled the paths at\nall, the bug still exists.\n\nfpregs_lock is necessary when editing the FPU registers or a task's FP\nstate but it is not necessary for fpu_inherit_perms(). The only write\nof any FP state in fpu_inherit_perms() is for the new child which is\nnot running yet and cannot context switch or be borrowed by a kernel\nthread yet. Hence, fpregs_lock is not protecting anything in the new\nchild until clone() completes and can be dropped earlier. The siglock\nstill needs to be acquired by fpu_inherit_perms() as the read of the\nparent's permissions has to be serialised.\n\n  [ bp: Cleanup splat. ]"
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: x86/fpu: Eliminar el bloqueo de fpregs antes de heredar los permisos de FPU Mike Galbraith informó lo siguiente contra una antigua bifurcación de preempt-rt, pero el mismo problema también se aplica al árbol preempt-rt actual. ERROR: función inactiva llamada desde un contexto no válido en kernel/locking/spinlock_rt.c:46 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd preempt_count: 1, expected: 0 Profundidad de anidamiento de RCU: 0, expected: 0 Preempción deshabilitada en: fpu_clone CPU: 6 PID: 1 Comm: systemd Tainted: GE (no publicado) Rastreo de llamadas:   dump_stack_lvl ? fpu_clone __might_resched rt_spin_lock fpu_clone ? copy_thread ? copy_process ? shmem_alloc_inode ? kmem_cache_alloc ? kernel_clone ? __do_sys_clone ? do_syscall_64 ? __x64_sys_rt_sigprocmask ? syscall_exit_to_user_mode ? do_syscall_64 ? syscall_exit_to_user_mode ? do_syscall_64 ? syscall_exit_to_user_mode ? do_syscall_64 ? exc_page_fault ? entry_SYSCALL_64_after_hwframe   Mike dice: El problema se debe a que fpu_inherit_perms() se llama bajo fpregs_lock() y a que alcanzamos spin_lock_irq() debido a que fpu_state_size_dynamic() devuelve verdadero a pesar de que la clave estática __fpu_state_size_dynamic nunca se ha habilitado. La evaluación de Mike parece correcta. fpregs_lock en un kernel PREEMPT_RT deshabilita la preempción, por lo que llamar a spin_lock_irq() en fpu_inherit_perms() no es seguro. Este problema existe desde la confirmación 9e798e9aa14c (\"x86/fpu: Preparar fpu_clone() para funciones habilitadas dinámicamente\"). Aunque el informe de error original no debería haber habilitado las rutas, el error persiste. fpregs_lock es necesario al editar los registros de FPU o el estado de FP de una tarea, pero no es necesario para fpu_inherit_perms(). La única escritura de cualquier estado de FP en fpu_inherit_perms() es para el nuevo hijo, que aún no se está ejecutando y aún no puede cambiar de contexto ni ser tomado prestado por un hilo del kernel. Por lo tanto, fpregs_lock no protege nada en el nuevo hijo hasta que clone() se complete y pueda eliminarse antes. El siglock aún debe ser adquirido por fpu_inherit_perms(), ya que la lectura de los permisos del padre debe serializarse. [bp: Limpieza splat.]"
    }
  ],
  "lastModified": "2026-06-17T05:19:08.250",
  "configurations": [
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