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CVE-2026-89767 (GCVE-0-2026-89767)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:47 – Updated: 2026-09-13 06:34
VLAI
Title
ovl: fix double end_creating() on the casefold-mismatch path
Summary
In the Linux kernel, the following vulnerability has been resolved: ovl: fix double end_creating() on the casefold-mismatch path ovl_create_real() releases the new dentry twice when the casefold consistency check fails. The S_IFDIR branch calls end_creating() and sets err, then falls through to the common out: label which calls end_creating() on the same dentry again: case S_IFDIR: newdentry = ovl_do_mkdir(ofs, dir, newdentry, attr->mode); err = PTR_ERR_OR_ZERO(newdentry); if (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) { pr_warn_ratelimited(...); end_creating(newdentry); /* first */ err = -EINVAL; } break; ... if (err) goto out; ... out: if (err) { end_creating(newdentry); /* second, same dentry */ return ERR_PTR(err); } end_creating() is end_dirop(), which does inode_unlock() on the parent and dput() on the dentry, so the parent directory's i_rwsem is unlocked twice and the dentry is put twice. The second unlock releases a lock that is not held, which is what wedges every later creation under that parent, and the second dput() drops a reference that was never taken. The branch was added by commit dfc7da402ccc ("ovl: Check for casefold consistency when creating new dentries") as a bare dput(), which already released the reference twice; commit fe497f0759e0 ("VFS: change vfs_mkdir() to unlock on failure.") converted both sites to end_creating(), adding the double unlock. This is reachable by an unprivileged user. The casefold consistency of the layers is validated at mount time in ovl_parse_layer(), and again on every lookup in ovl_lookup_single(), but ofs->workdir is the internal "work" subdirectory created inside the user-supplied workdir, and that subdirectory is not re-checked. Marking it casefolded after the mount therefore makes every ovl_create_temp() inherit the wrong state - and that path reaches ovl_create_real() through ovl_start_creating_temp(), which uses start_creating() with a generated name and so never runs the lookup-time check. unshare -Urm mount -t tmpfs -o casefold=utf8-12.1.0 tmpfs mnt mkdir -p mnt/lower/d mnt/upper mnt/work mnt/merged mount -t overlay ovl -o lowerdir=mnt/lower,\ upperdir=mnt/upper,workdir=mnt/work mnt/merged chattr +F mnt/work/work mkdir mnt/merged/d/sub # directory copy-up overlayfs: wrong inherited casefold (work/#5) and the next copy-up blocks forever on the parent's i_rwsem: mkdir D start_creating+0x65/0xb0 ovl_start_creating_temp+0xb0/0xe0 [overlay] ovl_create_temp+0xa3/0x1d0 [overlay] ovl_copy_up_one+0x1f1c/0x21c0 [overlay] ovl_copy_up_flags+0xf5/0x140 [overlay] ovl_create_object+0xb7/0x220 [overlay] ovl_mkdir+0x23/0x40 [overlay] Drop the end_creating() from the branch and let out: own the cleanup, which is what every other error path in this function already does.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: dfc7da402ccc92d6e4b01a4778a3f15f2496b9af , < 2fa220bc0f84597cb6de665e5b5021c5901ddf00 (git)
Affected: dfc7da402ccc92d6e4b01a4778a3f15f2496b9af , < b1aa8ab78a8e87aee9e306971465408e059f839a (git)
Affected: dfc7da402ccc92d6e4b01a4778a3f15f2496b9af , < 077ab8985ee278c3d8618182d335b0f0cd919e16 (git)
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Linux Linux Affected: 6.18
Unaffected: 0 , < 6.18 (semver)
Unaffected: 6.18.51 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/overlayfs/dir.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "dfc7da402ccc92d6e4b01a4778a3f15f2496b9af",
              "versionType": "git"
            },
            {
              "lessThan": "b1aa8ab78a8e87aee9e306971465408e059f839a",
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              "version": "dfc7da402ccc92d6e4b01a4778a3f15f2496b9af",
              "versionType": "git"
            },
            {
              "lessThan": "077ab8985ee278c3d8618182d335b0f0cd919e16",
              "status": "affected",
              "version": "dfc7da402ccc92d6e4b01a4778a3f15f2496b9af",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/overlayfs/dir.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.18"
            },
            {
              "lessThan": "6.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.51",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\novl: fix double end_creating() on the casefold-mismatch path\n\novl_create_real() releases the new dentry twice when the casefold\nconsistency check fails.  The S_IFDIR branch calls end_creating() and\nsets err, then falls through to the common out: label which calls\nend_creating() on the same dentry again:\n\n\tcase S_IFDIR:\n\t\tnewdentry = ovl_do_mkdir(ofs, dir, newdentry, attr-\u003emode);\n\t\terr = PTR_ERR_OR_ZERO(newdentry);\n\t\tif (!err \u0026\u0026 ofs-\u003ecasefold != ovl_dentry_casefolded(newdentry)) {\n\t\t\tpr_warn_ratelimited(...);\n\t\t\tend_creating(newdentry);\t/* first */\n\t\t\terr = -EINVAL;\n\t\t}\n\t\tbreak;\n\t...\n\tif (err)\n\t\tgoto out;\n\t...\n out:\n\tif (err) {\n\t\tend_creating(newdentry);\t/* second, same dentry */\n\t\treturn ERR_PTR(err);\n\t}\n\nend_creating() is end_dirop(), which does inode_unlock() on the parent\nand dput() on the dentry, so the parent directory\u0027s i_rwsem is unlocked\ntwice and the dentry is put twice.  The second unlock releases a lock\nthat is not held, which is what wedges every later creation under that\nparent, and the second dput() drops a reference that was never taken.\n\nThe branch was added by commit dfc7da402ccc (\"ovl: Check for casefold\nconsistency when creating new dentries\") as a bare dput(), which already\nreleased the reference twice; commit fe497f0759e0 (\"VFS: change\nvfs_mkdir() to unlock on failure.\") converted both sites to\nend_creating(), adding the double unlock.\n\nThis is reachable by an unprivileged user.  The casefold consistency of\nthe layers is validated at mount time in ovl_parse_layer(), and again on\nevery lookup in ovl_lookup_single(), but ofs-\u003eworkdir is the internal\n\"work\" subdirectory created inside the user-supplied workdir, and that\nsubdirectory is not re-checked.  Marking it casefolded after the mount\ntherefore makes every ovl_create_temp() inherit the wrong state - and\nthat path reaches ovl_create_real() through ovl_start_creating_temp(),\nwhich uses start_creating() with a generated name and so never runs the\nlookup-time check.\n\n  unshare -Urm\n  mount -t tmpfs -o casefold=utf8-12.1.0 tmpfs mnt\n  mkdir -p mnt/lower/d mnt/upper mnt/work mnt/merged\n  mount -t overlay ovl -o lowerdir=mnt/lower,\\\n        upperdir=mnt/upper,workdir=mnt/work mnt/merged\n  chattr +F mnt/work/work\n  mkdir mnt/merged/d/sub\t\t# directory copy-up\n\n  overlayfs: wrong inherited casefold (work/#5)\n\nand the next copy-up blocks forever on the parent\u0027s i_rwsem:\n\n  mkdir           D  start_creating+0x65/0xb0\n                     ovl_start_creating_temp+0xb0/0xe0 [overlay]\n                     ovl_create_temp+0xa3/0x1d0 [overlay]\n                     ovl_copy_up_one+0x1f1c/0x21c0 [overlay]\n                     ovl_copy_up_flags+0xf5/0x140 [overlay]\n                     ovl_create_object+0xb7/0x220 [overlay]\n                     ovl_mkdir+0x23/0x40 [overlay]\n\nDrop the end_creating() from the branch and let out: own the cleanup,\nwhich is what every other error path in this function already does."
        }
      ],
      "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 in overlayfs ovl_create_real() on the S_IFDIR casefold-mismatch path, reached from local mkdir/creat copy-up (ovl_mkdir \u2192 ovl_create_object \u2192 ovl_copy_up_one \u2192 ovl_create_temp). An unprivileged user can mount overlay on tmpfs in a user+mount namespace; this is not a network packet path.\nAC:L - The attacker fully controls the overlay mount, the post-mount chattr +F on the internal work/ workdir, and the mkdir that forces directory copy-up. The mismatch is deterministic with no race or victim state beyond the attacker\u0027s control.\nPR:L - Overlayfs sets FS_USERNS_MOUNT, so a normal local user can unshare a user and mount namespace, mount overlay, and reach ovl_create_real without init-namespace root. The commit\u0027s unshare -Urm reproducer matches this unprivileged path.\nUI:N - The attacker mounts the overlay, marks the internal workdir casefolded, and issues mkdir themselves. No separate victim action is required.\nS:U - Double end_creating() corrupts kernel VFS locking and dentry references on the local host. This stays within the kernel\u0027s security authority and is not a VM escape, IOMMU bypass, or other cross-boundary impact.\nC:H - end_creating() is end_dirop(), which inode_unlock()s the parent and dput()s the dentry. The extra dput can free or underflow a still-used dentry, and the extra unlock corrupts i_rwsem so concurrent VFS operations can race, enabling kernel memory disclosure.\nI:H - Double dput plus double inode_unlock of the parent i_rwsem break directory serialization and dentry lifetime. That enables use-after-free and unsynchronized create/lookup on the workdir, a high-integrity kernel memory-corruption primitive.\nA:H - The extra unlock leaves the workdir i_rwsem corrupt so later copy-up/create sleeps uninterruptibly in D state, and the extra dput/UAF can oops or panic the kernel. Either outcome is high availability impact."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-13T06:34:10.053Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/2fa220bc0f84597cb6de665e5b5021c5901ddf00"
        },
        {
          "url": "https://git.kernel.org/stable/c/b1aa8ab78a8e87aee9e306971465408e059f839a"
        },
        {
          "url": "https://git.kernel.org/stable/c/077ab8985ee278c3d8618182d335b0f0cd919e16"
        }
      ],
      "title": "ovl: fix double end_creating() on the casefold-mismatch path",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89767",
    "datePublished": "2026-09-11T19:47:07.353Z",
    "dateReserved": "2026-09-11T19:38:34.764Z",
    "dateUpdated": "2026-09-13T06:34:10.053Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-89767",
      "date": "2026-09-13",
      "epss": "0.00151",
      "percentile": "0.04588"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-89767\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-09-11T20:20:07.960\",\"lastModified\":\"2026-09-13T07:17:41.050\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\novl: fix double end_creating() on the casefold-mismatch path\\n\\novl_create_real() releases the new dentry twice when the casefold\\nconsistency check fails.  The S_IFDIR branch calls end_creating() and\\nsets err, then falls through to the common out: label which calls\\nend_creating() on the same dentry again:\\n\\n\\tcase S_IFDIR:\\n\\t\\tnewdentry = ovl_do_mkdir(ofs, dir, newdentry, attr-\u003emode);\\n\\t\\terr = PTR_ERR_OR_ZERO(newdentry);\\n\\t\\tif (!err \u0026\u0026 ofs-\u003ecasefold != ovl_dentry_casefolded(newdentry)) {\\n\\t\\t\\tpr_warn_ratelimited(...);\\n\\t\\t\\tend_creating(newdentry);\\t/* first */\\n\\t\\t\\terr = -EINVAL;\\n\\t\\t}\\n\\t\\tbreak;\\n\\t...\\n\\tif (err)\\n\\t\\tgoto out;\\n\\t...\\n out:\\n\\tif (err) {\\n\\t\\tend_creating(newdentry);\\t/* second, same dentry */\\n\\t\\treturn ERR_PTR(err);\\n\\t}\\n\\nend_creating() is end_dirop(), which does inode_unlock() on the parent\\nand dput() on the dentry, so the parent directory\u0027s i_rwsem is unlocked\\ntwice and the dentry is put twice.  The second unlock releases a lock\\nthat is not held, which is what wedges every later creation under that\\nparent, and the second dput() drops a reference that was never taken.\\n\\nThe branch was added by commit dfc7da402ccc (\\\"ovl: Check for casefold\\nconsistency when creating new dentries\\\") as a bare dput(), which already\\nreleased the reference twice; commit fe497f0759e0 (\\\"VFS: change\\nvfs_mkdir() to unlock on failure.\\\") converted both sites to\\nend_creating(), adding the double unlock.\\n\\nThis is reachable by an unprivileged user.  The casefold consistency of\\nthe layers is validated at mount time in ovl_parse_layer(), and again on\\nevery lookup in ovl_lookup_single(), but ofs-\u003eworkdir is the internal\\n\\\"work\\\" subdirectory created inside the user-supplied workdir, and that\\nsubdirectory is not re-checked.  Marking it casefolded after the mount\\ntherefore makes every ovl_create_temp() inherit the wrong state - and\\nthat path reaches ovl_create_real() through ovl_start_creating_temp(),\\nwhich uses start_creating() with a generated name and so never runs the\\nlookup-time check.\\n\\n  unshare -Urm\\n  mount -t tmpfs -o casefold=utf8-12.1.0 tmpfs mnt\\n  mkdir -p mnt/lower/d mnt/upper mnt/work mnt/merged\\n  mount -t overlay ovl -o lowerdir=mnt/lower,\\\\\\n        upperdir=mnt/upper,workdir=mnt/work mnt/merged\\n  chattr +F mnt/work/work\\n  mkdir mnt/merged/d/sub\\t\\t# directory copy-up\\n\\n  overlayfs: wrong inherited casefold (work/#5)\\n\\nand the next copy-up blocks forever on the parent\u0027s i_rwsem:\\n\\n  mkdir           D  start_creating+0x65/0xb0\\n                     ovl_start_creating_temp+0xb0/0xe0 [overlay]\\n                     ovl_create_temp+0xa3/0x1d0 [overlay]\\n                     ovl_copy_up_one+0x1f1c/0x21c0 [overlay]\\n                     ovl_copy_up_flags+0xf5/0x140 [overlay]\\n                     ovl_create_object+0xb7/0x220 [overlay]\\n                     ovl_mkdir+0x23/0x40 [overlay]\\n\\nDrop the end_creating() from the branch and let out: own the cleanup,\\nwhich is what every other error path in this function already does.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/overlayfs/dir.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"dfc7da402ccc92d6e4b01a4778a3f15f2496b9af\",\"lessThan\":\"2fa220bc0f84597cb6de665e5b5021c5901ddf00\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"dfc7da402ccc92d6e4b01a4778a3f15f2496b9af\",\"lessThan\":\"b1aa8ab78a8e87aee9e306971465408e059f839a\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"dfc7da402ccc92d6e4b01a4778a3f15f2496b9af\",\"lessThan\":\"077ab8985ee278c3d8618182d335b0f0cd919e16\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/overlayfs/dir.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"6.18\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"6.18\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.51\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2.4\",\"lessThanOrEqual\":\"7.2.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.3-rc1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":7.8,\"baseSeverity\":\"HIGH\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":5.9}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/077ab8985ee278c3d8618182d335b0f0cd919e16\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/2fa220bc0f84597cb6de665e5b5021c5901ddf00\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/b1aa8ab78a8e87aee9e306971465408e059f839a\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-13T06:53:04+00:00",
      "cve": "CVE-2026-89767",
      "id": "CVE-2026-89767",
      "initial_release_date": "2026-09-11T19:47:07.353000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel overlayfs: Denial of Service due to double unlock during directory creation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89767.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "not set",
      "current_release_date": "2026-09-12T16:21:52Z",
      "cve": "CVE-2026-89767",
      "id": "CVE-2026-89767",
      "initial_release_date": "2026-09-12T16:21:52Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89767",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89767.json",
      "version": "2"
    }
  }
}



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