CVE-2026-74576

Estado: RecibidaAlta (7.5)—

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

mm/slab: prevent unbounded recursion in free path with new kmalloc type

Commit 280ea9c3154b ("mm/slab: avoid allocating slabobj_ext array from its own slab") avoided recursive allocation of obj_exts from kmalloc caches of the same size, by bumping the obj_exts array's allocation size whenever the array size equals the size of the object being allocated.

However, as reported by Danielle Costantino and Shakeel Butt, even slabs from kmalloc caches of different sizes can form a cycle by allocating obj_exts arrays from each other [1]:

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With memory allocation profiling, this allows unbounded recursion in the free path and led to a stack overflow on a production host in the Meta fleet [1]:

It is proposed [1] to resolve this issue by always serving the obj_exts array allocation from kmalloc caches (or large kmalloc) of sizes larger than the object size. However, as pointed out by Vlastimil Babka [2], this can waste an excessive amount of memory as slabs from large kmalloc sizes (e.g. kmalloc-8k) generally need obj_exts arrays much smaller than the object size.

Therefore, rather than bumping the size, let us take a different approach; disallow formation of cycles between kmalloc types when allocating obj_exts arrays. Currently, all obj_exts arrays are served from normal kmalloc caches. Cycles cannot be created if obj_exts arrays of normal kmalloc caches are served from a special kmalloc type that can never have obj_exts arrays.

To achieve this, create a new kmalloc type called KMALLOC_NO_OBJ_EXT. KMALLOC_NO_OBJ_EXT caches are created with SLAB_NO_OBJ_EXT flag when either 1) memory allocation profiling is not permanently disabled, or 2) kmalloc types with a priority higher than KMALLOC_CGROUP are aliased with KMALLOC_NORMAL.

Sheaf bootstrapping for KMALLOC_NO_OBJ_EXT caches now must be deferred because allocation of a barn can trigger obj_exts array allocation of normal kmalloc caches when the KMALLOC_NO_OBJ_EXT cache for that size is not ready yet. For simplicity, perform bootstrapping of sheaves for all kmalloc caches later.

Introduce a new slab alloc flag, SLAB_ALLOC_NO_OBJ_EXT, to prevent allocation of obj_exts arrays, and let kmalloc_slab() override the type to KMALLOC_NO_OBJ_EXT when specified. Note that kmalloc_type() remains unchanged because kmalloc_flags() bypasses the kmalloc fastpath.

Do not pass SLAB_ALLOC_NO_RECURSE to kmalloc_flags() in alloc_slab_obj_exts() and instead use SLAB_ALLOC_NO_OBJ_EXT only when the objects are allocated from normal kmalloc caches. While this prevents unbounded recursive allocation of obj_exts, it allows KMALLOC_NO_OBJ_EXT caches to have sheaves.

Since sheaf allocations specify SLAB_ALLOC_NO_RECURSE that prevents allocation of both sheaves and obj_exts arrays, the recursion depth is bounded.

obj_exts arrays for non- ---truncated---

Detalles técnicos trazas, registros y código del informe original

  What happened: a KMALLOC_NORMAL slab's obj_exts array (used by
  allocation profiling / memcg accounting) is itself kmalloc()'d from a
  KMALLOC_NORMAL cache, so the "slab holds another slab's obj_exts array"
  relation can form cycles. With sizeof(struct slabobj_ext) == 16 and
  the host's geometry:

  - kmalloc-512 has 64 objects/slab -> array is 64*16 == 1024 bytes,
    served from kmalloc-1k;
  - kmalloc-1k  has 32 objects/slab -> array is 32*16 ==  512 bytes,
    served from kmalloc-512.

  A kmalloc-512 slab and a kmalloc-1k slab therefore hold each other's
  obj_exts array.  Discarding one frees the other's array, which empties
  and discards that slab, which frees the first's array, and so on:
  __free_slab() -> free_slab_obj_exts() -> kfree() -> discard_slab() ->
  __free_slab() recurses along the cycle until the stack is exhausted.

  BUG: TASK stack guard page was hit
  Oops: stack guard page
  RIP: 0010:kfree+0x8/0x5d0
  Call Trace:
   __free_slab+0x66/0xc0
   kfree+0x3f0/0x5d0
   ... ( ~125x __free_slab <-> kfree ) ...
   <kernel driver freeing a resource>
   do_syscall_64

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Puntuación base: 7.5

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.67%
Percentil entre todas las CVEs puntuadas: 50
Fecha de la puntuación: 6/10/2026

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).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1190 Exploit Public-Facing Applicationinitial access60 %
Impacto principalT1499 Endpoint Denial of Serviceimpact55 %

Inferido por reglas deterministas a partir del vector CVSS y la CWE. Solo orientativo.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network Traffic Vulnerability Scanning Privileged Account Management Network Segmentation Limit Access to Resource Over Network Application Isolation and Sandboxing

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux Kernel^AI

Referencias

JSON original (NVD)

Mostrar

{
  "id": "CVE-2026-74576",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.5,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4b8736964640fe160724e7135dc62883bddcdace",
              "lessThan": "3e71bfbdd3fd81ee9fefd867fdb2be62bade4140",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "4b8736964640fe160724e7135dc62883bddcdace",
              "lessThan": "d01e88d421a6d07f35235600a43fbd0e551cf292",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "4b8736964640fe160724e7135dc62883bddcdace",
              "lessThan": "ebefca49e4c69df24ba9307bfe0806230301d5c6",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "4b8736964640fe160724e7135dc62883bddcdace",
              "lessThan": "d9e6a7623938968e3752b67e37eaff097e559a54",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "include/linux/slab.h",
            "mm/slab.h",
            "mm/slab_common.c",
            "mm/slub.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.10"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.10",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "6.12.103",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.18.44",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "status": "unaffected",
              "version": "7.1.8",
              "versionType": "semver",
              "lessThanOrEqual": "7.1.*"
            },
            {
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "include/linux/slab.h",
            "mm/slab.h",
            "mm/slab_common.c",
            "mm/slub.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-08-15T13:18:03.290",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/3e71bfbdd3fd81ee9fefd867fdb2be62bade4140",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/d01e88d421a6d07f35235600a43fbd0e551cf292",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/d9e6a7623938968e3752b67e37eaff097e559a54",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/ebefca49e4c69df24ba9307bfe0806230301d5c6",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/slab: prevent unbounded recursion in free path with new kmalloc type\n\nCommit 280ea9c3154b (\"mm/slab: avoid allocating slabobj_ext array from\nits own slab\") avoided recursive allocation of obj_exts from kmalloc\ncaches of the same size, by bumping the obj_exts array's allocation\nsize whenever the array size equals the size of the object being\nallocated.\n\nHowever, as reported by Danielle Costantino and Shakeel Butt,\neven slabs from kmalloc caches of different sizes can form a cycle\nby allocating obj_exts arrays from each other [1]:\n\n  What happened: a KMALLOC_NORMAL slab's obj_exts array (used by\n  allocation profiling / memcg accounting) is itself kmalloc()'d from a\n  KMALLOC_NORMAL cache, so the \"slab holds another slab's obj_exts array\"\n  relation can form cycles. With sizeof(struct slabobj_ext) == 16 and\n  the host's geometry:\n\n  - kmalloc-512 has 64 objects/slab -> array is 64*16 == 1024 bytes,\n    served from kmalloc-1k;\n  - kmalloc-1k  has 32 objects/slab -> array is 32*16 ==  512 bytes,\n    served from kmalloc-512.\n\n  A kmalloc-512 slab and a kmalloc-1k slab therefore hold each other's\n  obj_exts array.  Discarding one frees the other's array, which empties\n  and discards that slab, which frees the first's array, and so on:\n  __free_slab() -> free_slab_obj_exts() -> kfree() -> discard_slab() ->\n  __free_slab() recurses along the cycle until the stack is exhausted.\n\nWith memory allocation profiling, this allows unbounded recursion\nin the free path and led to a stack overflow on a production host in\nthe Meta fleet [1]:\n\n  BUG: TASK stack guard page was hit\n  Oops: stack guard page\n  RIP: 0010:kfree+0x8/0x5d0\n  Call Trace:\n   __free_slab+0x66/0xc0\n   kfree+0x3f0/0x5d0\n   ... ( ~125x __free_slab <-> kfree ) ...\n   <kernel driver freeing a resource>\n   do_syscall_64\n\nIt is proposed [1] to resolve this issue by always serving the obj_exts\narray allocation from kmalloc caches (or large kmalloc) of sizes larger\nthan the object size. However, as pointed out by Vlastimil Babka [2],\nthis can waste an excessive amount of memory as slabs from large\nkmalloc sizes (e.g. kmalloc-8k) generally need obj_exts arrays much\nsmaller than the object size.\n\nTherefore, rather than bumping the size, let us take a different\napproach; disallow formation of cycles between kmalloc types when\nallocating obj_exts arrays. Currently, all obj_exts arrays are served\nfrom normal kmalloc caches. Cycles cannot be created if obj_exts arrays\nof normal kmalloc caches are served from a special kmalloc type that can\nnever have obj_exts arrays.\n\nTo achieve this, create a new kmalloc type called KMALLOC_NO_OBJ_EXT.\nKMALLOC_NO_OBJ_EXT caches are created with SLAB_NO_OBJ_EXT flag when\neither 1) memory allocation profiling is not permanently disabled,\nor 2) kmalloc types with a priority higher than KMALLOC_CGROUP are\naliased with KMALLOC_NORMAL.\n\nSheaf bootstrapping for KMALLOC_NO_OBJ_EXT caches now must be deferred\nbecause allocation of a barn can trigger obj_exts array allocation of\nnormal kmalloc caches when the KMALLOC_NO_OBJ_EXT cache for that size\nis not ready yet. For simplicity, perform bootstrapping of sheaves for\nall kmalloc caches later.\n\nIntroduce a new slab alloc flag, SLAB_ALLOC_NO_OBJ_EXT, to prevent\nallocation of obj_exts arrays, and let kmalloc_slab() override the type\nto KMALLOC_NO_OBJ_EXT when specified. Note that kmalloc_type() remains\nunchanged because kmalloc_flags() bypasses the kmalloc fastpath.\n\nDo not pass SLAB_ALLOC_NO_RECURSE to kmalloc_flags() in\nalloc_slab_obj_exts() and instead use SLAB_ALLOC_NO_OBJ_EXT only when\nthe objects are allocated from normal kmalloc caches. While this\nprevents unbounded recursive allocation of obj_exts, it allows\nKMALLOC_NO_OBJ_EXT caches to have sheaves.\n\nSince sheaf allocations specify SLAB_ALLOC_NO_RECURSE that prevents\nallocation of both sheaves and obj_exts arrays, the recursion depth\nis bounded.\n\nobj_exts arrays for non-\n---truncated---"
    }
  ],
  "lastModified": "2026-08-17T06:19:56.017",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}