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

cxl: Fix race of nvdimm_bus object when creating nvdimm objects

Found issue during running of cxl-translate.sh unit test. Adding a 3s
sleep right before the test seems to make the issue reproduce fairly
consistently. The cxl_translate module has dependency on cxl_acpi and
causes orphaned nvdimm objects to reprobe after cxl_acpi is removed.
The nvdimm_bus object is registered by the cxl_nvb object when
cxl_acpi_probe() is called. With the nvdimm_bus object missing,
__nd_device_register() will trigger NULL pointer dereference when
accessing the dev->parent that points to &nvdimm_bus->dev.

[ 192.884510] BUG: kernel NULL pointer dereference, address: 000000000000006c
[ 192.895383] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20250812-19.fc42 08/12/2025
[ 192.897721] Workqueue: cxl_port cxl_bus_rescan_queue [cxl_core]
[ 192.899459] RIP: 0010:kobject_get+0xc/0x90
[ 192.924871] Call Trace:
[ 192.925959] <TASK>
[ 192.926976] ? pm_runtime_init+0xb9/0xe0
[ 192.929712] __nd_device_register.part.0+0x4d/0xc0 [libnvdimm]
[ 192.933314] __nvdimm_create+0x206/0x290 [libnvdimm]
[ 192.936662] cxl_nvdimm_probe+0x119/0x1d0 [cxl_pmem]
[ 192.940245] cxl_bus_probe+0x1a/0x60 [cxl_core]
[ 192.943349] really_probe+0xde/0x380

This patch also relies on the previous change where
devm_cxl_add_nvdimm_bridge() is called from drivers/cxl/pmem.c instead
of drivers/cxl/core.c to ensure the dependency of cxl_acpi on cxl_pmem.

1. Set probe_type of cxl_nvb to PROBE_FORCE_SYNCHRONOUS to ensure the
driver is probed synchronously when add_device() is called.
2. Add a check in __devm_cxl_add_nvdimm_bridge() to ensure that the
cxl_nvb driver is attached during cxl_acpi_probe().
3. Take the cxl_root uport_dev lock and the cxl_nvb->dev lock in
devm_cxl_add_nvdimm() before checking nvdimm_bus is valid.
4. Set cxl_nvdimm flag to CXL_NVD_F_INVALIDATED so cxl_nvdimm_probe()
will exit with -EBUSY.

The removal of cxl_nvdimm devices should prevent any orphaned devices
from probing once the nvdimm_bus is gone.

[ dj: Fixed 0-day reported kdoc issue. ]
[ dj: Fix cxl_nvb reference leak on error. Gregory (kreview-0811365) ]

En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:

cxl: Corrige la condición de carrera del objeto nvdimm_bus al crear objetos nvdimm

Se encontró el problema durante la ejecución de la prueba unitaria cxl-translate.sh. Añadir un retardo de 3s justo antes de la prueba parece hacer que el problema se reproduzca de forma bastante consistente. El módulo cxl_translate tiene una dependencia de cxl_acpi y provoca que los objetos nvdimm huérfanos se vuelvan a sondear después de que se elimine cxl_acpi. El objeto nvdimm_bus es registrado por el objeto cxl_nvb cuando se llama a cxl_acpi_probe(). Al faltar el objeto nvdimm_bus, __nd_device_register() activará una desreferencia de puntero NULL al acceder a dev-&gt;parent que apunta a &amp;nvdimm_bus-&gt;dev.

[ 192.884510] BUG: desreferencia de puntero NULL del kernel, dirección: 000000000000006c
[ 192.895383] Nombre del hardware: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20250812-19.fc42 08/12/2025
[ 192.897721] Cola de trabajo: cxl_port cxl_bus_rescan_queue [cxl_core]
[ 192.899459] RIP: 0010:kobject_get+0xc/0x90
[ 192.924871] Traza de llamada:
[ 192.925959]
[ 192.926976] ? pm_runtime_init+0xb9/0xe0
[ 192.929712] __nd_device_register.part.0+0x4d/0xc0 [libnvdimm]
[ 192.933314] __nvdimm_create+0x206/0x290 [libnvdimm]
[ 192.936662] cxl_nvdimm_probe+0x119/0x1d0 [cxl_pmem]
[ 192.940245] cxl_bus_probe+0x1a/0x60 [cxl_core]
[ 192.943349] really_probe+0xde/0x380

Este parche también se basa en el cambio anterior donde se llama a devm_cxl_add_nvdimm_bridge() desde drivers/cxl/pmem.c en lugar de drivers/cxl/core.c para asegurar la dependencia de cxl_acpi en cxl_pmem.

1. Establecer probe_type de cxl_nvb a PROBE_FORCE_SYNCHRONOUS para asegurar que el controlador sea sondeado sincrónicamente cuando se llama a add_device().
2. Añadir una comprobación en __devm_cxl_add_nvdimm_bridge() para asegurar que el controlador cxl_nvb esté adjunto durante cxl_acpi_probe().
3. Tomar el bloqueo cxl_root uport_dev y el bloqueo cxl_nvb-&gt;dev en devm_cxl_add_nvdimm() antes de comprobar que nvdimm_bus es válido.
4. Establecer el indicador cxl_nvdimm a CXL_NVD_F_INVALIDATED para que cxl_nvdimm_probe() salga con -EBUSY.

La eliminación de dispositivos cxl_nvdimm debería evitar que cualquier dispositivo huérfano se sondee una vez que el nvdimm_bus haya desaparecido.

[ dj: Se corrigió el problema de kdoc reportado el día 0. ]
[ dj: Corrige la fuga de referencia de cxl_nvb en caso de error. Gregory (kreview-0811365) ]