ublk: clear VM_MAYWRITE on read-only ublk char device mmap

{
  "id": "57224364aea896210c23f8c8703323cbc80e2ef8c08d705bcffa4136c4f3e6ff",
  "url": "https://osv.dev/vulnerability/CVE-2026-89793",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ublk: clear VM_MAYWRITE on read-only ublk char device mmap",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ublk: clear VM_MAYWRITE on read-only ublk char device mmap ublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never clears VM_MAYWRITE on the resulting read-only mapping. This allows a userspace daemon to mmap the per-queue command buffer PROT_READ, then upgrade it to PROT_WRITE via mprotect(), since VM_MAYWRITE was never cleared. The command buffer holds struct ublksrv_io_desc entries that are kernel-written ABI; a writable mapping lets an unprivileged daemon process corrupt fields such as addr, op_flags, nr_sectors, and start_sector. Same bug class as the drm/panthor and drm/vc4 VM_MAYWRITE fixes, and the 2026-08-13 ptp/vmclock fix (a5edadbae57e). Verified via mprotect() PoC: before the fix, a PROT_READ mapping can be upgraded to PROT_READ|PROT_WRITE and a write into the command buffer corrupts io_desc fields (confirmed under KASAN). After the fix, mprotect() returns -EACCES.",
    "evidence": "osv:CVE-2026-89793",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.6.157",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.110",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.51",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.2.5",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-89793",
      "aliases": [
        "CVE-2026-89793"
      ],
      "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": "71f28f3136aff5890cd56de78abc673f8393cad9"
                },
                {
                  "fixed": "be41733c24be58e2a1ef718c80fafdfb98a40d5e"
                },
                {
                  "fixed": "5befd06a72216869b607cf7724a4f16c6a2d3999"
                },
                {
                  "fixed": "e373c1acdbcf88cec533ece9f589020adaed0a78"
                },
                {
                  "fixed": "fa5e1bc673ca59722608af67b27e65dba0c97926"
                },
                {
                  "fixed": "6e2b571b0a54755b06e092501913e1dfefe75d6c"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89793.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.0.0"
                },
                {
                  "fixed": "6.6.157"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.110"
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            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.51"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.2.5"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89793.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:29.824574199Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/5befd06a72216869b607cf7724a4f16c6a2d3999",
        "https://git.kernel.org/stable/c/6e2b571b0a54755b06e092501913e1dfefe75d6c",
        "https://git.kernel.org/stable/c/be41733c24be58e2a1ef718c80fafdfb98a40d5e",
        "https://git.kernel.org/stable/c/e373c1acdbcf88cec533ece9f589020adaed0a78",
        "https://git.kernel.org/stable/c/fa5e1bc673ca59722608af67b27e65dba0c97926",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89793.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89793",
        "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/2026/89xxx/CVE-2026-89793.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-89793",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 496820,
  "published_at": "2026-09-16T09:54:33.678+00:00"
}