// For flags

CVE-2024-36892

mm/slub: avoid zeroing outside-object freepointer for single free

Severity Score

"-"
*CVSS v-

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

Track
*SSVC
Descriptions

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

mm/slub: avoid zeroing outside-object freepointer for single free

Commit 284f17ac13fe ("mm/slub: handle bulk and single object freeing
separately") splits single and bulk object freeing in two functions
slab_free() and slab_free_bulk() which leads slab_free() to call
slab_free_hook() directly instead of slab_free_freelist_hook().

If `init_on_free` is set, slab_free_hook() zeroes the object.
Afterward, if `slub_debug=F` and `CONFIG_SLAB_FREELIST_HARDENED` are
set, the do_slab_free() slowpath executes freelist consistency
checks and try to decode a zeroed freepointer which leads to a
"Freepointer corrupt" detection in check_object().

During bulk free, slab_free_freelist_hook() isn't affected as it always
sets it objects freepointer using set_freepointer() to maintain its
reconstructed freelist after `init_on_free`.

For single free, object's freepointer thus needs to be avoided when
stored outside the object if `init_on_free` is set. The freepointer left
as is, check_object() may later detect an invalid pointer value due to
objects overflow.

To reproduce, set `slub_debug=FU init_on_free=1 log_level=7` on the
command line of a kernel build with `CONFIG_SLAB_FREELIST_HARDENED=y`.

dmesg sample log:
[ 10.708715] =============================================================================
[ 10.710323] BUG kmalloc-rnd-05-32 (Tainted: G B T ): Freepointer corrupt
[ 10.712695] -----------------------------------------------------------------------------
[ 10.712695]
[ 10.712695] Slab 0xffffd8bdc400d580 objects=32 used=4 fp=0xffff9d9a80356f80 flags=0x200000000000a00(workingset|slab|node=0|zone=2)
[ 10.716698] Object 0xffff9d9a80356600 @offset=1536 fp=0x7ee4f480ce0ecd7c
[ 10.716698]
[ 10.716698] Bytes b4 ffff9d9a803565f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 10.720703] Object ffff9d9a80356600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 10.720703] Object ffff9d9a80356610: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 10.724696] Padding ffff9d9a8035666c: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 10.724696] Padding ffff9d9a8035667c: 00 00 00 00 ....
[ 10.724696] FIX kmalloc-rnd-05-32: Object at 0xffff9d9a80356600 not freed

En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: mm/slub: evita poner a cero el puntero libre de objetos externos para un solo commit libre 284f17ac13fe ("mm/slub: maneja la liberación masiva y de objetos individuales por separado") divide la liberación de objetos únicos y masivos en dos funciones slab_free() y slab_free_bulk() lo que lleva a slab_free() a llamar a slab_free_hook() directamente en lugar de slab_free_freelist_hook(). Si se establece `init_on_free`, slab_free_hook() pone a cero el objeto. Luego, si se configuran `slub_debug=F` y `CONFIG_SLAB_FREELIST_HARDENED`, la ruta lenta do_slab_free() ejecuta comprobaciones de coherencia de la lista libre e intenta decodificar un freepointer puesto a cero, lo que conduce a una detección de "Freepointer corrupto" en check_object(). Durante la liberación masiva, slab_free_freelist_hook() no se ve afectado ya que siempre establece el puntero libre de sus objetos usando set_freepointer() para mantener su lista libre reconstruida después de `init_on_free`. Para un solo libre, el puntero libre del objeto debe evitarse cuando se almacena fuera del objeto si está configurado "init_on_free". El puntero libre se deja como está, check_object() puede detectar más adelante un valor de puntero no válido debido a un desbordamiento de objetos. Para reproducir, configure `slub_debug=FU init_on_free=1 log_level=7` en la línea de comando de una compilación del kernel con `CONFIG_SLAB_FREELIST_HARDENED=y`. Registro de muestra de dmesg: [10.708715] ============================================ ================================== [10.710323] ERROR kmalloc-rnd-05-32 (Contaminado: GBT) : Freepointer corrupto [10.712695] -------------------------------------------- --------------------------------- [ 10.712695] [ 10.712695] Losa 0xffffd8bdc400d580 objetos=32 usados=4 fp=0xffff9d9a80356f80 flags=0x200000000000a00(workingset|slab|node=0|zone=2) [ 10.716698] Objeto 0xffff9d9a80356600 @offset=1536 fp=0x7ee4f480ce0ecd7c [ 10.716698] [ 10.716698] Bytes b4 9d9a803565f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ [ 10.720703] Objeto ffff9d9a80356600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ........ ........ [ 10.720703] Objeto ffff9d9a80356610: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ [ 10.724696] Relleno ffff9d9a8035666c: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ [ 10.724696] Relleno ffff9d9a8035667c: 00 00 00 00 .... [ 10.724696 ] FIX kmalloc-rnd-05-32: Objeto en 0xffff9d9a80356600 no liberado

*Credits: N/A
CVSS Scores
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Scope
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Confidentiality
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* Common Vulnerability Scoring System
SSVC
  • Decision:Track
Exploitation
None
Automatable
No
Tech. Impact
Partial
* Organization's Worst-case Scenario
Timeline
  • 2024-05-30 CVE Reserved
  • 2024-05-30 CVE Published
  • 2024-05-31 EPSS Updated
  • 2024-12-19 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 6.8 < 6.8.10
Search vendor "Linux" for product "Linux Kernel" and version " >= 6.8 < 6.8.10"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 6.8 < 6.9
Search vendor "Linux" for product "Linux Kernel" and version " >= 6.8 < 6.9"
en
Affected