# cveboard — Historical CVE brief

## Instructions for the operator's AI
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Fix information unknown; no fixed version is derived here. Missing information does not prove that no fix exists.
Exploitation unknown; this catalogue does not assess exploitation.

## Source facts (JSON-quoted data)
CNA source text (English)
id: "CVE-2026-89768"
idYear: 2026
status: "PUBLISHED"
publishedAt: "2026-09-11T19:47:08.119Z"
updatedAt: "2026-10-19T08:52:21.786Z"
importedAt: "2026-10-24T01:58:35.090Z"
snapshot: {"id":"cve_2026-10-24_midnight_baseline","at":"2026-10-24T00:00:00.000Z","source":"https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z"}
url: "https://cveboard.org/cve/CVE-2026-89768"
json: "https://cveboard.org/cve/CVE-2026-89768.json"
sourceURL: "https://www.cve.org/CVERecord?id=CVE-2026-89768"
title: "fs: fix user path of nested backing files"
summary: "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&user_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: [{"versions":[{"version":"5b6aa9a843205da92d860e5011a7b29062a76b8f","status":"affected","versionType":"git","lessThan":"88c927a63dc717b6d46b20fe13ea713916e49089"},{"version":"5dfcb15974e7d0f96aca278dd9f1b85df91523ef","status":"affected","versionType":"git","lessThan":"c03114634d342648bd34910aa8fb88007e92cc3c"},{"version":"6af36aeb147a06dea47c49859cd6ca5659aeb987","status":"affected","versionType":"git","lessThan":"a35cc21355734e1acb89973d9be90ca8e4c3ed2f"},{"version":"6af36aeb147a06dea47c49859cd6ca5659aeb987","status":"affected","versionType":"git","lessThan":"f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d"},{"version":"41c5b269af8b1f0bffcab7766a793f294ae6764e","status":"affected","versionType":"git"},{"version":"27e795afba0018b0ea9460dbad4bd706d1ba5ee0","status":"affected","versionType":"git"},{"version":"6.12.95","status":"affected","versionType":"semver","lessThan":"6.12.109"},{"version":"6.18.38","status":"affected","versionType":"semver","lessThan":"6.18.50"},{"version":"6.6.144","status":"affected","versionType":"semver","lessThan":"6.7"},{"version":"7.0.4","status":"affected","versionType":"semver","lessThan":"7.1"}],"vendor":"Linux","product":"Linux","defaultStatus":"unaffected"},{"versions":[{"version":"7.1","status":"affected"},{"version":"0","status":"unaffected","versionType":"semver","lessThan":"7.1"},{"version":"6.12.109","status":"unaffected","versionType":"semver","lessThanOrEqual":"6.12.*"},{"version":"6.18.50","status":"unaffected","versionType":"semver","lessThanOrEqual":"6.18.*"},{"version":"7.2.4","status":"unaffected","versionType":"semver","lessThanOrEqual":"7.2.*"},{"version":"7.3","status":"unaffected","versionType":"original_commit_for_fix","lessThanOrEqual":"*"}],"vendor":"Linux","product":"Linux","defaultStatus":"affected"}]

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GitHub Advisory Database: https://github.com/advisories (CC BY 4.0)
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