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CVE-2026-89768 (GCVE-0-2026-89768)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:47 – Updated: 2026-09-11 19:47
VLAI
Title
fs: fix user path of nested backing files
Summary
In the Linux kernel, the following vulnerability has been resolved: fs: fix user path of nested backing files backing_file_open() derives the path to be stored in the new backing file from user_file->f_path. This is incorrect when user_file itself is a backing file, which is the case for nested stacking filesystems, e.g. overlayfs mounts where the lowerdir of one overlayfs is the merged directory of another. Since commit def3ae83da02 ("fs: store real path instead of fake path in backing file f_path") the f_path of a backing file holds the real path of the intermediate layer, not the path that the user opened. Commit 924577e4f6ca ("ovl: Fix nested backing file paths") fixed this for such configurations by passing file_user_path() from ovl_open_realfile(). However, commit 6af36aeb147a ("lsm: add backing_file LSM hooks") changed the first argument of backing_file_open() from the user path back to the user file and derived the path from user_file->f_path again, silently re-introducing the problem. As a result, files mapped through a nested overlayfs show the wrong path in /proc/<pid>/maps and in perf/ftrace mmap records. For example, with two nested overlayfs mounts: mkdir -p /ovl/{lower,upper,work,merged} /ovl/nested echo hello > /ovl/lower/foo mount -t overlay overlay \ -o lowerdir=/ovl/lower,upperdir=/ovl/upper,workdir=/ovl/work \ /ovl/merged # at least two lowerdirs are needed when upperdir is nonexistent mount -t overlay overlay \ -o lowerdir=/ovl/merged:/ovl/lower /ovl/nested mapping /ovl/nested/foo shows a disconnected path instead of the user path: # readlink /proc/self/fd/3 /ovl/nested/foo # grep foo /proc/self/maps 7f6e2c100000-7f6e2c101000 r--s 00000000 00:24 15813027 /foo The bogus path is derived from the f_path of the intermediate backing file, whose mount is a private clone that d_path() cannot resolve. Fix this by using file_user_path(), which returns the outermost user-visible path for backing files and falls back to &user_file->f_path for regular files. This restores the behavior of commit 924577e4f6ca ("ovl: Fix nested backing file paths") for overlayfs and also fixes the same problem for the other backing_file_open() callers, fuse passthrough and erofs ishare, when their user file is itself a backing file. backing_tmpfile_open() has the same pattern but is not affected: it is only called by ovl_create_tmpfile() for the upper layer, and another overlayfs is rejected as upperdir by the DCACHE_OP_REAL check in ovl_mount_dir_check(), so its user_file can never be a backing file.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 5b6aa9a843205da92d860e5011a7b29062a76b8f , < 88c927a63dc717b6d46b20fe13ea713916e49089 (git)
Affected: 5dfcb15974e7d0f96aca278dd9f1b85df91523ef , < c03114634d342648bd34910aa8fb88007e92cc3c (git)
Affected: 6af36aeb147a06dea47c49859cd6ca5659aeb987 , < a35cc21355734e1acb89973d9be90ca8e4c3ed2f (git)
Affected: 6af36aeb147a06dea47c49859cd6ca5659aeb987 , < f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d (git)
Affected: 41c5b269af8b1f0bffcab7766a793f294ae6764e (git)
Affected: 27e795afba0018b0ea9460dbad4bd706d1ba5ee0 (git)
Affected: 6.12.95 , < 6.12.109 (semver)
Affected: 6.18.38 , < 6.18.50 (semver)
Affected: 6.6.144 , < 6.7 (semver)
Affected: 7.0.4 , < 7.1 (semver)
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Linux Linux Affected: 7.1
Unaffected: 0 , < 7.1 (semver)
Unaffected: 6.12.109 , ≤ 6.12.* (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs: fix user path of nested backing files\n\nbacking_file_open() derives the path to be stored in the new backing\nfile from user_file-\u003ef_path.  This is incorrect when user_file itself\nis a backing file, which is the case for nested stacking filesystems,\ne.g. overlayfs mounts where the lowerdir of one overlayfs is the merged\ndirectory of another.  Since commit def3ae83da02 (\"fs: store real path\ninstead of fake path in backing file f_path\") the f_path of a backing\nfile holds the real path of the intermediate layer, not the path that\nthe user opened.\n\nCommit 924577e4f6ca (\"ovl: Fix nested backing file paths\") fixed this\nfor such configurations by passing file_user_path() from\novl_open_realfile().  However, commit 6af36aeb147a (\"lsm: add\nbacking_file LSM hooks\") changed the first argument of\nbacking_file_open() from the user path back to the user file and\nderived the path from user_file-\u003ef_path again, silently re-introducing\nthe problem.\n\nAs a result, files mapped through a nested overlayfs show the wrong\npath in /proc/\u003cpid\u003e/maps and in perf/ftrace mmap records.  For example,\nwith two nested overlayfs mounts:\n\n  mkdir -p /ovl/{lower,upper,work,merged} /ovl/nested\n  echo hello \u003e /ovl/lower/foo\n  mount -t overlay overlay \\\n\t-o lowerdir=/ovl/lower,upperdir=/ovl/upper,workdir=/ovl/work \\\n\t/ovl/merged\n  # at least two lowerdirs are needed when upperdir is nonexistent\n  mount -t overlay overlay \\\n\t-o lowerdir=/ovl/merged:/ovl/lower /ovl/nested\n\nmapping /ovl/nested/foo shows a disconnected path instead of the user\npath:\n\n  # readlink /proc/self/fd/3\n  /ovl/nested/foo\n  # grep foo /proc/self/maps\n  7f6e2c100000-7f6e2c101000 r--s 00000000 00:24 15813027 /foo\n\nThe bogus path is derived from the f_path of the intermediate backing\nfile, whose mount is a private clone that d_path() cannot resolve.\n\nFix this by using file_user_path(), which returns the outermost\nuser-visible path for backing files and falls back to\n\u0026user_file-\u003ef_path for regular files.  This restores the behavior of\ncommit 924577e4f6ca (\"ovl: Fix nested backing file paths\") for\noverlayfs and also fixes the same problem for the other\nbacking_file_open() callers, fuse passthrough and erofs ishare, when\ntheir user file is itself a backing file.\n\nbacking_tmpfile_open() has the same pattern but is not affected: it is\nonly called by ovl_create_tmpfile() for the upper layer, and another\noverlayfs is rejected as upperdir by the DCACHE_OP_REAL check in\novl_mount_dir_check(), so its user_file can never be a backing file."
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    "datePublished": "2026-09-11T19:47:08.119Z",
    "dateReserved": "2026-09-11T19:38:34.764Z",
    "dateUpdated": "2026-09-11T19:47:08.119Z",
    "state": "PUBLISHED"
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      "cve": "CVE-2026-89768",
      "id": "msrc_CVE-2026-89768",
      "initial_release_date": "2026-09-13T01:04:55.000Z",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "fs: fix user path of nested backing files",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-89768.json",
      "version": "2"
    },
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Since commit def3ae83da02 (\\\"fs: store real path\\ninstead of fake path in backing file f_path\\\") the f_path of a backing\\nfile holds the real path of the intermediate layer, not the path that\\nthe user opened.\\n\\nCommit 924577e4f6ca (\\\"ovl: Fix nested backing file paths\\\") fixed this\\nfor such configurations by passing file_user_path() from\\novl_open_realfile().  However, commit 6af36aeb147a (\\\"lsm: add\\nbacking_file LSM hooks\\\") changed the first argument of\\nbacking_file_open() from the user path back to the user file and\\nderived the path from user_file-\u003ef_path again, silently re-introducing\\nthe problem.\\n\\nAs a result, files mapped through a nested overlayfs show the wrong\\npath in /proc/\u003cpid\u003e/maps and in perf/ftrace mmap records.  For example,\\nwith two nested overlayfs mounts:\\n\\n  mkdir -p /ovl/{lower,upper,work,merged} /ovl/nested\\n  echo hello \u003e /ovl/lower/foo\\n  mount -t overlay overlay \\\\\\n\\t-o lowerdir=/ovl/lower,upperdir=/ovl/upper,workdir=/ovl/work \\\\\\n\\t/ovl/merged\\n  # at least two lowerdirs are needed when upperdir is nonexistent\\n  mount -t overlay overlay \\\\\\n\\t-o lowerdir=/ovl/merged:/ovl/lower /ovl/nested\\n\\nmapping /ovl/nested/foo shows a disconnected path instead of the user\\npath:\\n\\n  # readlink /proc/self/fd/3\\n  /ovl/nested/foo\\n  # grep foo /proc/self/maps\\n  7f6e2c100000-7f6e2c101000 r--s 00000000 00:24 15813027 /foo\\n\\nThe bogus path is derived from the f_path of the intermediate backing\\nfile, whose mount is a private clone that d_path() cannot resolve.\\n\\nFix this by using file_user_path(), which returns the outermost\\nuser-visible path for backing files and falls back to\\n\u0026user_file-\u003ef_path for regular files.  This restores the behavior of\\ncommit 924577e4f6ca (\\\"ovl: Fix nested backing file paths\\\") for\\noverlayfs and also fixes the same problem for the other\\nbacking_file_open() callers, fuse passthrough and erofs ishare, when\\ntheir user file is itself a backing file.\\n\\nbacking_tmpfile_open() has the same pattern but is not affected: it is\\nonly called by ovl_create_tmpfile() for the upper layer, and another\\noverlayfs is rejected as upperdir by the DCACHE_OP_REAL check in\\novl_mount_dir_check(), so its user_file can never be a backing file.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/backing-file.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"5b6aa9a843205da92d860e5011a7b29062a76b8f\",\"lessThan\":\"88c927a63dc717b6d46b20fe13ea713916e49089\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5dfcb15974e7d0f96aca278dd9f1b85df91523ef\",\"lessThan\":\"c03114634d342648bd34910aa8fb88007e92cc3c\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"6af36aeb147a06dea47c49859cd6ca5659aeb987\",\"lessThan\":\"a35cc21355734e1acb89973d9be90ca8e4c3ed2f\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"6af36aeb147a06dea47c49859cd6ca5659aeb987\",\"lessThan\":\"f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"41c5b269af8b1f0bffcab7766a793f294ae6764e\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"27e795afba0018b0ea9460dbad4bd706d1ba5ee0\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"6.12.95\",\"lessThan\":\"6.12.109\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"6.18.38\",\"lessThan\":\"6.18.50\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"6.6.144\",\"lessThan\":\"6.7\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"7.0.4\",\"lessThan\":\"7.1\",\"versionType\":\"semver\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/backing-file.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"7.1\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"7.1\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.109\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.50\",\"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\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/88c927a63dc717b6d46b20fe13ea713916e49089\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a35cc21355734e1acb89973d9be90ca8e4c3ed2f\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/c03114634d342648bd34910aa8fb88007e92cc3c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-09-15T04:56:05+00:00",
      "cve": "CVE-2026-89768",
      "id": "CVE-2026-89768",
      "initial_release_date": "2026-09-11T19:47:08.119000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel: Information disclosure via incorrect path derivation in nested overlayfs",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89768.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "low",
      "current_release_date": "2026-09-12T16:21:49Z",
      "cve": "CVE-2026-89768",
      "id": "CVE-2026-89768",
      "initial_release_date": "2026-09-12T16:21:49Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89768",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89768.json",
      "version": "2"
    }
  }
}



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