CVE-2026-89768

CVE CVE-2026-89768EUVD EUVD-2026-76680Veröffentlicht 2026-09-11T19:47:08.000Z

Was das Advisory beschreibt

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.

Quelle: EUVD (ENISA), im Wortlaut der Meldung.

Produkte, die das Advisory nennt

Diese Angaben stammen aus der Meldung selbst, nicht aus einer Prüfung durch uns.

• Linux — Linux 41c5b269af8b1f0bffcab7766a793f294ae6764e; 6af36aeb147a06dea47c49859cd6ca5659aeb987 <a35cc21355734e1acb89973d9be90ca8e4c3ed2f; patch: 7.2.4; 6.12.95 <6.12.109; patch: 6.18.50; 5dfcb15974e7d0f96aca278dd9f1b85df91523ef <c03114634d342648bd34910aa8fb88007e92cc3c; patch: 6.12.109; 5b6aa9a843205da92d860e5011a7b29062a76b8f <88c927a63dc717b6d46b20fe13ea713916e49089; 7.1; 6.6.144 <6.7; 6.18.38 <6.18.50; patch: 7.3-rc1; 7.0.4 <7.1; 6af36aeb147a06dea47c49859cd6ca5659aeb987 <f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d; 27e795afba0018b0ea9460dbad4bd706d1ba5ee0; patch: 0

Die genannten Versionen sind die Angabe der Meldung. Patchlage vergleicht keine Versionsnummern und leitet aus ihnen keine Aussage ab — welche Version installiert ist, muss ein Mensch nachsehen.

Im Produktkatalog geführt

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• Linux — Linux

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