{"id":"CVE-2026-89768","summary":"fs: fix user path of nested backing files","details":"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.","modified":"2026-10-28T02:31:02.449785439Z","published":"2026-09-11T19:47:08.119Z","related":["openSUSE-SU-2026:11880-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89768.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/88c927a63dc717b6d46b20fe13ea713916e49089"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a35cc21355734e1acb89973d9be90ca8e4c3ed2f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c03114634d342648bd34910aa8fb88007e92cc3c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89768.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89768"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"5b6aa9a843205da92d860e5011a7b29062a76b8f"},{"fixed":"88c927a63dc717b6d46b20fe13ea713916e49089"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"5dfcb15974e7d0f96aca278dd9f1b85df91523ef"},{"fixed":"c03114634d342648bd34910aa8fb88007e92cc3c"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"6af36aeb147a06dea47c49859cd6ca5659aeb987"},{"fixed":"a35cc21355734e1acb89973d9be90ca8e4c3ed2f"},{"fixed":"f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"6.12.95"},{"fixed":"6.12.109"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"6.18.38"},{"fixed":"6.18.50"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"6.6.144"},{"fixed":"6.7"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"7.0.4"},{"fixed":"7.1"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"41c5b269af8b1f0bffcab7766a793f294ae6764e"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"27e795afba0018b0ea9460dbad4bd706d1ba5ee0"}]}],"versions":["v6.12.108","v6.12.107","v6.12.106","v6.12.105","v6.12.104","v6.12.103","v6.12.102","v6.12.101","v6.12.100","v6.12.99","v6.12.98","v6.12.97","v6.12.96","v6.12.95","v6.18.49","v6.18.48","v6.18.47","v6.18.46","v6.18.45","v6.18.44","v6.18.43","v6.18.42","v6.18.41","v6.18.40","v6.18.39","v6.18.38","v6.6.160","v6.6.159","v6.6.158","v6.6.157","v6.6.156","v6.6.155","v6.6.154","v6.6.153","v6.6.152","v6.6.151","v6.6.150","v6.6.149","v6.6.148","v6.6.147","v6.6.146","v6.6.145","v6.6.144","v7.0.14","v7.0.13","v7.0.12","v7.0.11","v7.0.10","v7.0.9","v7.0.8","v7.0.7","v7.0.6","v7.0.5","v7.0.4"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89768.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.12.109"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.50"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89768.json"}}],"schema_version":"1.9.2"}