KVM: Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot

{
  "id": "c034924d3bd65143d042ec203204872e27cf5bab2fdff962b5501f7905bdf409",
  "url": "https://osv.dev/vulnerability/CVE-2025-68810",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "KVM: Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: KVM: Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot Reject attempts to disable KVM_MEM_GUEST_MEMFD on a memslot that was initially created with a guest_memfd binding, as KVM doesn't support toggling KVM_MEM_GUEST_MEMFD on existing memslots. KVM prevents enabling KVM_MEM_GUEST_MEMFD, but doesn't prevent clearing the flag. Failure to reject the new memslot results in a use-after-free due to KVM not unbinding from the guest_memfd instance. Unbinding on a FLAGS_ONLY change is easy enough, and can/will be done as a hardening measure (in anticipation of KVM supporting dirty logging on guest_memfd at some point), but fixing the use-after-free would only address the immediate symptom. ================================================================== BUG: KASAN: slab-use-after-free in kvm_gmem_release+0x362/0x400 [kvm] Write of size 8 at addr ffff8881111ae908 by task repro/745 CPU: 7 UID: 1000 PID: 745 Comm: repro Not tainted 6.18.0-rc6-115d5de2eef3-next-kasan #3 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: dump_stack_lvl+0x51/0x60 print_report+0xcb/0x5c0 kasan_report+0xb4/0xe0 kvm_gmem_release+0x362/0x400 [kvm] __fput+0x2fa/0x9d0 task_work_run+0x12c/0x200 do_exit+0x6ae/0x2100 do_group_exit+0xa8/0x230 __x64_sys_exit_group+0x3a/0x50 x64_sys_call+0x737/0x740 do_syscall_64+0x5b/0x900 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f581f2eac31 Allocated by",
    "evidence": "osv:CVE-2025-68810",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.64",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.3",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-68810",
      "aliases": [
        "CVE-2025-68810"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "a7800aa80ea4d5356b8474c2302812e9d4926fa6"
                },
                {
                  "fixed": "89dbbe6ff323fc34659621a577fe0af913f47386"
                },
                {
                  "fixed": "cb51bef465d8ec60a968507330e01020e35dc127"
                },
                {
                  "fixed": "9935df5333aa503a18de5071f53762b65c783c4c"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-68810.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.8.0"
                },
                {
                  "fixed": "6.12.64"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.3"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-68810.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.366283084Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/89dbbe6ff323fc34659621a577fe0af913f47386",
        "https://git.kernel.org/stable/c/9935df5333aa503a18de5071f53762b65c783c4c",
        "https://git.kernel.org/stable/c/cb51bef465d8ec60a968507330e01020e35dc127",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/68xxx/CVE-2025-68810.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-68810",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/68xxx/CVE-2025-68810.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-68810",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 489798,
  "published_at": "2026-01-13T15:29:16.475+00:00"
}