{"id":"AZL-100442","summary":"CVE-2026-89768 affecting package kernel 6.6.150.1-1","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":"2026-09-13T06:06:36Z","published":"2026-09-11T20:20:08Z","upstream":["CVE-2026-89768"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89768"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.150.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-100442.json"}}],"schema_version":"1.9.0"}