CVE-2026-89493 (GCVE-0-2026-89493)
Vulnerability from cvelistv5
Published
2026-09-11 19:43
Modified
2026-10-19 08:47
Severity ?
8.8 (High) - CVSS:3.1/AV:N/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: ocfs2: validate rl_used against rl_count in refcount block validator ocfs2_find_refcount_rec_in_rl() walks the on-disk refcount record array with: for (; i < le16_to_cpu(rb->rf_records.rl_used); i++) { rec = &rb->rf_records.rl_recs[i]; ... rl_recs[] lives in a single metadata block (4096 bytes on the common configuration), so its real capacity is fixed by ocfs2_refcount_recs_per_rb(sb) (247 records for a 4K block with the 16-byte ocfs2_refcount_rec). rl_used and rl_count are both read directly off disk by ocfs2_validate_refcount_block() and are never checked against that capacity, nor against each other, before any refcount/reflink/CoW operation walks the array. A crafted (or corrupted) refcount block with rl_used == 0xffff makes the loop above walk far past the end of the block, dereferencing rl_recs[i] for i up to 65534. The resulting index is then handed to the sibling ocfs2_insert_refcount_rec(), whose insert-shift does: if (index < le16_to_cpu(rf_list->rl_used)) memmove(&rf_list->rl_recs[index + 1], &rf_list->rl_recs[index], (le16_to_cpu(rf_list->rl_used) - index) * sizeof(struct ocfs2_refcount_rec)); i.e. a memmove() of up to (0xffff - index) * 16 bytes (~1 MiB) from an offset already past the block. This is reachable from an ordinary reflink (FICLONE) against a crafted/corrupted ocfs2 image: attaching an extent whose cpos sorts past every real record in the leaf forces the lookup to run off the end instead of returning early on a match. The attacker model is local: CAP_SYS_ADMIN mounting a crafted or corrupted ocfs2 image, or a raw write to the block device backing an already-mounted ocfs2 filesystem. ocfs2_validate_refcount_block() already validates the block's ECC, signature, rf_blkno and rf_fs_generation, but never rl_count/rl_used against the block's actual on-disk capacity. This is the same class of gap that ocfs2_validate_extent_block() (fs/ocfs2/alloc.c) already closes for the sibling extent-list header, which checks both the record capacity and the "used" bound before any code walks h_list.l_recs[]: if (le16_to_cpu(eb->h_list.l_count) != ocfs2_extent_recs_per_eb(sb)) { rc = ocfs2_error(...); goto bail; } if (le16_to_cpu(eb->h_list.l_next_free_rec) > le16_to_cpu(eb->h_list.l_count)) { rc = ocfs2_error(...); goto bail; } Add the equivalent pair of checks to ocfs2_validate_refcount_block(): reject a refcount block whose rl_count does not match the fixed per-block capacity returned by ocfs2_refcount_recs_per_rb(), and reject rl_used > rl_count. Both checks are skipped when OCFS2_REFCOUNT_TREE_FL is set, because in that case the same union bytes hold an ocfs2_extent_list (rf_list), not the refcount record list (rf_records) -- that layout is already validated separately by ocfs2_validate_extent_block() when the referenced extent block is read. This mirrors the existing "!(rb->rf_flags & OCFS2_REFCOUNT_TREE_FL)" guard used elsewhere in this file (e.g. ocfs2_get_refcount_rec()) to decide whether rf_records or rf_list is the live member of the union. With this in place, a forged rl_used/rl_count is caught at block validation time (ocfs2_error()), consistent with every other corruption check in this function, instead of driving an out-of-bounds read in ocfs2_find_refcount_rec_in_rl() and a subsequent out-of-bounds memmove() in ocfs2_insert_refcount_rec(). Verified against a crafted image on a v6.19 KASAN (KASAN_GENERIC) build: replaying the same reflink (FICLONE) reliably hit a KASAN report in __ocfs2_increase_refcount()/ocfs2_insert_refcount_rec() before this patch, and triggers no report once ocfs2_validate_refcount_block() rejects the forged rl_used/rl_count.
References
Impacted products
Vendor Product Version
Linux Linux Version: f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4
Version: f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4
Version: f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4
Version: f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4
Version: f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4
Version: f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4
Version: f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4
Version: f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ocfs2/refcounttree.c"
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          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "2.6.32"
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "5.10.270",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.221",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.188",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.109",
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
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              "version": "7.2.4",
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            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
                },
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                  "versionEndExcluding": "5.15.221",
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                },
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                  "versionEndExcluding": "6.6.157",
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                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nocfs2: validate rl_used against rl_count in refcount block validator\n\nocfs2_find_refcount_rec_in_rl() walks the on-disk refcount record array\nwith:\n\n\tfor (; i \u003c le16_to_cpu(rb-\u003erf_records.rl_used); i++) {\n\t\trec = \u0026rb-\u003erf_records.rl_recs[i];\n\t\t...\n\nrl_recs[] lives in a single metadata block (4096 bytes on the common\nconfiguration), so its real capacity is fixed by\nocfs2_refcount_recs_per_rb(sb) (247 records for a 4K block with the\n16-byte ocfs2_refcount_rec).  rl_used and rl_count are both read directly\noff disk by ocfs2_validate_refcount_block() and are never checked against\nthat capacity, nor against each other, before any refcount/reflink/CoW\noperation walks the array.\n\nA crafted (or corrupted) refcount block with rl_used == 0xffff makes the\nloop above walk far past the end of the block, dereferencing rl_recs[i]\nfor i up to 65534.  The resulting index is then handed to the sibling\nocfs2_insert_refcount_rec(), whose insert-shift does:\n\n\tif (index \u003c le16_to_cpu(rf_list-\u003erl_used))\n\t\tmemmove(\u0026rf_list-\u003erl_recs[index + 1],\n\t\t\t\u0026rf_list-\u003erl_recs[index],\n\t\t\t(le16_to_cpu(rf_list-\u003erl_used) - index) *\n\t\t\t sizeof(struct ocfs2_refcount_rec));\n\ni.e.  a memmove() of up to (0xffff - index) * 16 bytes (~1 MiB) from an\noffset already past the block.  This is reachable from an ordinary reflink\n(FICLONE) against a crafted/corrupted ocfs2 image: attaching an extent\nwhose cpos sorts past every real record in the leaf forces the lookup to\nrun off the end instead of returning early on a match.  The attacker model\nis local: CAP_SYS_ADMIN mounting a crafted or corrupted ocfs2 image, or a\nraw write to the block device backing an already-mounted ocfs2 filesystem.\n\nocfs2_validate_refcount_block() already validates the block\u0027s ECC,\nsignature, rf_blkno and rf_fs_generation, but never rl_count/rl_used\nagainst the block\u0027s actual on-disk capacity.  This is the same class of\ngap that ocfs2_validate_extent_block() (fs/ocfs2/alloc.c) already closes\nfor the sibling extent-list header, which checks both the record capacity\nand the \"used\" bound before any code walks h_list.l_recs[]:\n\n\tif (le16_to_cpu(eb-\u003eh_list.l_count) != ocfs2_extent_recs_per_eb(sb)) {\n\t\trc = ocfs2_error(...);\n\t\tgoto bail;\n\t}\n\n\tif (le16_to_cpu(eb-\u003eh_list.l_next_free_rec) \u003e\n\t    le16_to_cpu(eb-\u003eh_list.l_count)) {\n\t\trc = ocfs2_error(...);\n\t\tgoto bail;\n\t}\n\nAdd the equivalent pair of checks to ocfs2_validate_refcount_block():\nreject a refcount block whose rl_count does not match the fixed per-block\ncapacity returned by ocfs2_refcount_recs_per_rb(), and reject rl_used \u003e\nrl_count.  Both checks are skipped when OCFS2_REFCOUNT_TREE_FL is set,\nbecause in that case the same union bytes hold an ocfs2_extent_list\n(rf_list), not the refcount record list (rf_records) -- that layout is\nalready validated separately by ocfs2_validate_extent_block() when the\nreferenced extent block is read.  This mirrors the existing\n\"!(rb-\u003erf_flags \u0026 OCFS2_REFCOUNT_TREE_FL)\" guard used elsewhere in this\nfile (e.g.  ocfs2_get_refcount_rec()) to decide whether rf_records or\nrf_list is the live member of the union.\n\nWith this in place, a forged rl_used/rl_count is caught at block\nvalidation time (ocfs2_error()), consistent with every other corruption\ncheck in this function, instead of driving an out-of-bounds read in\nocfs2_find_refcount_rec_in_rl() and a subsequent out-of-bounds memmove()\nin ocfs2_insert_refcount_rec().\n\nVerified against a crafted image on a v6.19 KASAN (KASAN_GENERIC) build:\nreplaying the same reflink (FICLONE) reliably hit a KASAN report in\n__ocfs2_increase_refcount()/ocfs2_insert_refcount_rec() before this patch,\nand triggers no report once ocfs2_validate_refcount_block() rejects the\nforged rl_used/rl_count."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - OCFS2 registers export_operations and is commonly NFS-exported or ksmbd-shared on cluster storage; remote NFSv4.2 CLONE or ksmbd FSCTL_DUPLICATE_EXTENTS reaches vfs_clone_file_range\u2192ocfs2_remap_file_range, and NFS WRITE/truncate on refcounted files reaches ocfs2_get_refcount_rec() and the OOB walk/memmove.\nAC:L - A crafted refcount block with rl_used=0xffff plus FICLONE/clone or write/CoW whose cpos sorts past the real leaf records deterministically drives the OOB loop and memmove; the fix commit reproduced this under KASAN with no race or uncontrollable layout.\nPR:L - Triggering needs only write/clone permission on a file whose inode points at the forged refcount block (unprivileged local user or authenticated NFS/SMB client); ocfs2_remap_file_range and ocfs2_reflink_ioctl have no capability check, and planting on-disk metadata does not require init-namespace root.\nUI:N - Once the malformed refcount block is on an already-mounted or NFS/SMB-exported OCFS2 volume, the attacker issues clone, write, or truncate themselves; no separate victim mount, click, or administrator action is required at exploit time.\nS:U - The out-of-bounds read and write corrupt kernel memory in the host parsing the OCFS2 refcount block; impact stays within that kernel\u0027s security authority and does not cross a VM, container, or IOMMU boundary.\nC:H - ocfs2_find_refcount_rec_in_rl() indexes rl_recs[i] for i up to 65534 past a single 4K metadata block, performing an approximately 1 MiB out-of-bounds read of adjacent kernel memory and enabling high-bandwidth disclosure.\nI:H - ocfs2_insert_refcount_rec() memmove()s up to (0xffff-index)*16 bytes (~1 MiB) from and to offsets already past the block and writes rl_recs[index] out of bounds, which is an arbitrary kernel out-of-bounds write exploitable for control-flow hijacking.\nA:H - The same OOB access was reproduced as a KASAN fault in __ocfs2_increase_refcount()/ocfs2_insert_refcount_rec() and causes a kernel oops or panic, fully denying availability on the affected node."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:47:44.950Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/f882e9e32d017a6569b2996c63ba3864717788e6"
        },
        {
          "url": "https://git.kernel.org/stable/c/5593b63028cb43a6cda75a65ce1db95f00ea6857"
        },
        {
          "url": "https://git.kernel.org/stable/c/c8b02f4ee91e757b3fff556c7168b24b7ae55132"
        },
        {
          "url": "https://git.kernel.org/stable/c/97584e93fc49a2d59252ac60467e9279f11b1b5b"
        },
        {
          "url": "https://git.kernel.org/stable/c/af56e90cb546cb0c47bef059335365283f61d6a4"
        },
        {
          "url": "https://git.kernel.org/stable/c/0761d2c9494424469a0d30a9da3496ca010b0b2d"
        },
        {
          "url": "https://git.kernel.org/stable/c/04ead708e13ddcb9c39319cbe02a18cef99cb823"
        },
        {
          "url": "https://git.kernel.org/stable/c/4ca62df6bc0708947b48da3f6a712ecb8e73929c"
        }
      ],
      "title": "ocfs2: validate rl_used against rl_count in refcount block validator",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89493",
    "datePublished": "2026-09-11T19:43:44.803Z",
    "dateReserved": "2026-09-11T19:38:34.714Z",
    "dateUpdated": "2026-10-19T08:47:44.950Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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