CVE-2026-89966 (GCVE-0-2026-89966)
Vulnerability from cvelistv5
Published
2026-09-16 10:32
Modified
2026-10-19 08:55
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb_cma: fix null nodemask dereference in hugetlb_cma_alloc_frozen_folio alloc_buddy_hugetlb_folio_with_mpol() can pass a NULL nodemask to alloc_fresh_hugetlb_folio() as a fallback to allocate from all nodes. If order is gigantic, alloc_fresh_hugetlb_folio() propagates the NULL nodemask down to hugetlb_cma_alloc_frozen_folio() via alloc_gigantic_frozen_folio(). Additionally, hugetlb_cma_alloc_frozen_folio() previously attempted allocation on hugetlb_cma[nid] without verifying if nid is included in the caller's nodemask. Adding a node_isset(nid, *nodemask) check ensures the initial preferred node allocation honors the memory policy / nodemask. However, hugetlb_cma_alloc_frozen_folio() dereferences the nodemask in node_isset(nid, *nodemask) and for_each_node_mask(node, *nodemask), leading to a null pointer dereference kernel panic when nodemask is NULL. Fix this by checking if nodemask is NULL in hugetlb_cma_alloc_frozen_folio() and defaulting it to cpuset_current_mems_allowed. Enclose the allocation attempts within the cpuset seqcount retry loop so that if the cpuset changes concurrently during allocation, the attempts are retried using the updated nodemask. This ensures that the initial node check and fallback loop safely honor the task's cpuset without violating cpuset constraints or causing NULL pointer dereferences or unexpected allocation failures. From a userspace perspective, this bug allows an unprivileged user to crash the kernel (trigger a panic) by requesting a gigantic hugepage allocation with MPOL_PREFERRED_MANY on a system where CMA is only configured on a subset of NUMA nodes. This can be reproduced by booting a VM with two NUMA nodes, restricting CMA to Node 1 (e.g., hugetlb_cma=1:1G default_hugepagesz=1G hugepagesz=1G hugepages=0), and running a program that allocates a 1GB hugepage area without reserving, restricts allocation to Node 0 using mbind() with MPOL_PREFERRED_MANY, and triggers a page fault: void *ptr = mmap(NULL, 1UL << 30, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_HUGE_1GB | MAP_NORESERVE, -1, 0); unsigned long nodemask = 1; /* Node 0 */ mbind(ptr, 1UL << 30, MPOL_PREFERRED_MANY, &nodemask, sizeof(nodemask) * 8, 0); memset(ptr, 0, 1UL << 30); /* Trigger fault */ This results in a NULL pointer dereference: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page Oops: Oops: 0000 [#1] SMP NOPTI RIP: 0010:hugetlb_cma_alloc_frozen_folio+0x75/0x120 Call Trace: <TASK> only_alloc_fresh_hugetlb_folio.isra.0+0x2c/0x160 alloc_surplus_hugetlb_folio+0x6d/0x100 alloc_hugetlb_folio+0x3c5/0x660 hugetlb_no_page+0x3d9/0x650
References
Impacted products
Vendor Product Version
Linux Linux Version: eb02f14c4a2bf4c242d91c4a5d7fb57c3c0ad1b1
Version: eb02f14c4a2bf4c242d91c4a5d7fb57c3c0ad1b1
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/hugetlb_cma.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "10f616ef06c5bd2d656a0eebaf73f9b09d150c24",
              "status": "affected",
              "version": "eb02f14c4a2bf4c242d91c4a5d7fb57c3c0ad1b1",
              "versionType": "git"
            },
            {
              "lessThan": "7b8a8ae4dd176a232e973017d2aa3c536a7275e2",
              "status": "affected",
              "version": "eb02f14c4a2bf4c242d91c4a5d7fb57c3c0ad1b1",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "mm/hugetlb_cma.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.5",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/hugetlb_cma: fix null nodemask dereference in hugetlb_cma_alloc_frozen_folio\n\nalloc_buddy_hugetlb_folio_with_mpol() can pass a NULL nodemask to\nalloc_fresh_hugetlb_folio() as a fallback to allocate from all nodes.  If\norder is gigantic, alloc_fresh_hugetlb_folio() propagates the NULL\nnodemask down to hugetlb_cma_alloc_frozen_folio() via\nalloc_gigantic_frozen_folio().\n\nAdditionally, hugetlb_cma_alloc_frozen_folio() previously attempted\nallocation on hugetlb_cma[nid] without verifying if nid is included in the\ncaller\u0027s nodemask.  Adding a node_isset(nid, *nodemask) check ensures the\ninitial preferred node allocation honors the memory policy / nodemask.\n\nHowever, hugetlb_cma_alloc_frozen_folio() dereferences the nodemask in\nnode_isset(nid, *nodemask) and for_each_node_mask(node, *nodemask),\nleading to a null pointer dereference kernel panic when nodemask is NULL.\n\nFix this by checking if nodemask is NULL in\nhugetlb_cma_alloc_frozen_folio() and defaulting it to\ncpuset_current_mems_allowed.  Enclose the allocation attempts within the\ncpuset seqcount retry loop so that if the cpuset changes concurrently\nduring allocation, the attempts are retried using the updated nodemask. \nThis ensures that the initial node check and fallback loop safely honor\nthe task\u0027s cpuset without violating cpuset constraints or causing NULL\npointer dereferences or unexpected allocation failures.\n\nFrom a userspace perspective, this bug allows an unprivileged user to\ncrash the kernel (trigger a panic) by requesting a gigantic hugepage\nallocation with MPOL_PREFERRED_MANY on a system where CMA is only\nconfigured on a subset of NUMA nodes.\n\nThis can be reproduced by booting a VM with two NUMA nodes, restricting\nCMA to Node 1 (e.g., hugetlb_cma=1:1G default_hugepagesz=1G hugepagesz=1G\nhugepages=0), and running a program that allocates a 1GB hugepage area\nwithout reserving, restricts allocation to Node 0 using mbind() with\nMPOL_PREFERRED_MANY, and triggers a page fault:\n\n  void *ptr = mmap(NULL, 1UL \u003c\u003c 30, PROT_READ | PROT_WRITE,\n                   MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB |\n                   MAP_HUGE_1GB | MAP_NORESERVE, -1, 0);\n  unsigned long nodemask = 1; /* Node 0 */\n  mbind(ptr, 1UL \u003c\u003c 30, MPOL_PREFERRED_MANY, \u0026nodemask,\n        sizeof(nodemask) * 8, 0);\n  memset(ptr, 0, 1UL \u003c\u003c 30); /* Trigger fault */\n\nThis results in a NULL pointer dereference:\n\n  BUG: kernel NULL pointer dereference, address: 0000000000000000\n  #PF: supervisor read access in kernel mode\n  #PF: error_code(0x0000) - not-present page\n  Oops: Oops: 0000 [#1] SMP NOPTI\n  RIP: 0010:hugetlb_cma_alloc_frozen_folio+0x75/0x120\n  Call Trace:\n   \u003cTASK\u003e\n   only_alloc_fresh_hugetlb_folio.isra.0+0x2c/0x160\n   alloc_surplus_hugetlb_folio+0x6d/0x100\n   alloc_hugetlb_folio+0x3c5/0x660\n   hugetlb_no_page+0x3d9/0x650"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:55:39.844Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/10f616ef06c5bd2d656a0eebaf73f9b09d150c24"
        },
        {
          "url": "https://git.kernel.org/stable/c/7b8a8ae4dd176a232e973017d2aa3c536a7275e2"
        }
      ],
      "title": "mm/hugetlb_cma: fix null nodemask dereference in hugetlb_cma_alloc_frozen_folio",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89966",
    "datePublished": "2026-09-16T10:32:47.482Z",
    "dateReserved": "2026-09-11T19:38:34.778Z",
    "dateUpdated": "2026-10-19T08:55:39.844Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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