CVE-2026-89793 (GCVE-0-2026-89793)
Vulnerability from cvelistv5
Published
2026-09-16 09:54
Modified
2026-10-19 08:52
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 71f28f3136aff5890cd56de78abc673f8393cad9
Version: 71f28f3136aff5890cd56de78abc673f8393cad9
Version: 71f28f3136aff5890cd56de78abc673f8393cad9
Version: 71f28f3136aff5890cd56de78abc673f8393cad9
Version: 71f28f3136aff5890cd56de78abc673f8393cad9
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/block/ublk_drv.c"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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        },
        {
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          "product": "Linux",
          "programFiles": [
            "drivers/block/ublk_drv.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.0"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.110",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.51",
              "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": "6.6.157",
                  "versionStartIncluding": "6.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.110",
                  "versionStartIncluding": "6.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.51",
                  "versionStartIncluding": "6.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.5",
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                  "vulnerable": true
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "6.0",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nublk: clear VM_MAYWRITE on read-only ublk char device mmap\n\nublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never\nclears VM_MAYWRITE on the resulting read-only mapping. This allows\na userspace daemon to mmap the per-queue command buffer PROT_READ,\nthen upgrade it to PROT_WRITE via mprotect(), since VM_MAYWRITE was\nnever cleared.\n\nThe command buffer holds struct ublksrv_io_desc entries that are\nkernel-written ABI; a writable mapping lets an unprivileged daemon\nprocess corrupt fields such as addr, op_flags, nr_sectors, and\nstart_sector.\n\nSame bug class as the drm/panthor and drm/vc4 VM_MAYWRITE fixes, and\nthe 2026-08-13 ptp/vmclock fix (a5edadbae57e).\n\nVerified via mprotect() PoC: before the fix, a PROT_READ mapping can\nbe upgraded to PROT_READ|PROT_WRITE and a write into the command\nbuffer corrupts io_desc fields (confirmed under KASAN). After the\nfix, mprotect() returns -EACCES."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reached only through local syscalls: open of /dev/ublkcN (created via /dev/ublk-control), mmap(PROT_READ) of the per-queue command buffer in ublk_ch_mmap(), then mprotect(PROT_WRITE). There is no network, Bluetooth, or physical-bus path into this mmap handler.\nAC:L - The attacker fully controls every step: mmap PROT_READ, mprotect PROT_WRITE, and write through the remap_pfn_range PFNMAP. mprotect upgrades the VMA because VM_MAYWRITE was left set (mm/mprotect.c), with no race, special layout, or victim state required.\nPR:L - ublk_ctrl_add_dev() lets a caller without CAP_SYS_ADMIN create a device with UBLK_F_UNPRIVILEGED_DEV, and ublk_ch_open() has no capability check, so an ordinary local user or a delegated unprivileged ublk daemon can open /dev/ublkcN and mmap the command buffer.\nUI:N - The attacking process performs the full create/open/mmap/mprotect/write sequence itself and can issue I/O to its own ublk disk to drive kernel re-reads of the corrupted descriptors. No other user must mount, open, or otherwise interact.\nS:U - The corrupted io_cmd_buf pages and the ublk/block I/O path that consumes them all sit in the host kernel\u0027s security authority. This is standard local kernel memory corruption, not a VM, IOMMU, or hypervisor boundary escape.\nC:H - The kernel re-reads iod-\u003eop_flags via ublk_iod_is_shmem_zc() on completion; setting UBLK_IO_F_SHMEM_ZC skips ublk_unmap_io(), so READ bios complete with uninitialized request/page-cache pages. That is the same uninitialized kernel-memory leak UBLK_F_SUPPORT_ZERO_COPY was denied to unprivileged devices to prevent.\nI:H - After mprotect, userspace has a writable PFNMAP of kernel-allocated io_cmd_buf pages and can overwrite kernel-written ublksrv_io_desc fields (op_flags, addr, nr_sectors, start_sector). The kernel then trusts op_flags to skip map/unmap, corrupting the block I/O data path for every consumer of that ublk disk.\nA:H - Clearing SHMEM_ZC with a null io-\u003ebuf.addr forces ublk_start_io() into the mapped_bytes==0 requeue loop and stalls the request queue; completing I/O against corrupted descriptors or uninitialized pages can oops or hang the kernel. Attacker-triggerable kernel hang or crash is High."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:52:48.148Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/be41733c24be58e2a1ef718c80fafdfb98a40d5e"
        },
        {
          "url": "https://git.kernel.org/stable/c/5befd06a72216869b607cf7724a4f16c6a2d3999"
        },
        {
          "url": "https://git.kernel.org/stable/c/e373c1acdbcf88cec533ece9f589020adaed0a78"
        },
        {
          "url": "https://git.kernel.org/stable/c/fa5e1bc673ca59722608af67b27e65dba0c97926"
        },
        {
          "url": "https://git.kernel.org/stable/c/6e2b571b0a54755b06e092501913e1dfefe75d6c"
        }
      ],
      "title": "ublk: clear VM_MAYWRITE on read-only ublk char device mmap",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89793",
    "datePublished": "2026-09-16T09:54:33.678Z",
    "dateReserved": "2026-09-11T19:38:34.766Z",
    "dateUpdated": "2026-10-19T08:52:48.148Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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