{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-89768",
  "modified": "2026-10-07T14:35:31Z",
  "upstream": [
    "CVE-2026-89768"
  ],
  "published": "2026-09-11T19:47:07Z",
  "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->f_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->f_path again, silently re-introducing\nthe problem.\n\nAs a result, files mapped through a nested overlayfs show the wrong\npath in /proc/<pid>/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 > /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->f_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": [
    {
      "package": {
        "ecosystem": "Raspberry Pi OS:12",
        "name": "linux"
      },
      "versions": [
        "1:6.12.96-1+rpt1"
      ],
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "linux-image-6.12.96+rpt-rpi-2712",
            "binary_version": "1:6.12.96-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.96+rpt-rpi-v6",
            "binary_version": "1:6.12.96-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.96+rpt-rpi-v7",
            "binary_version": "1:6.12.96-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.96+rpt-rpi-v7l",
            "binary_version": "1:6.12.96-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.96+rpt-rpi-v8",
            "binary_version": "1:6.12.96-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.96+rpt-rpi-v8-rt",
            "binary_version": "1:6.12.96-1+rpt1"
          }
        ]
      },
      "database_specific": {
        "per_version": {
          "1:6.12.96-1+rpt1": {
            "linux_commit": "ae161617d7a4552fa91d03626b8d9f3696d17481",
            "upstream_version": "6.12.96",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.12.109"
          }
        }
      }
    },
    {
      "package": {
        "ecosystem": "Raspberry Pi OS:13",
        "name": "linux"
      },
      "versions": [
        "1:6.18.39-1+rpt1"
      ],
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "linux-image-6.18.39+rpt-rpi-2712",
            "binary_version": "1:6.18.39-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.18.39+rpt-rpi-v6",
            "binary_version": "1:6.18.39-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.18.39+rpt-rpi-v7",
            "binary_version": "1:6.18.39-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.18.39+rpt-rpi-v8",
            "binary_version": "1:6.18.39-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.18.39+rpt-rpi-v8-rt",
            "binary_version": "1:6.18.39-1+rpt1"
          }
        ]
      },
      "database_specific": {
        "per_version": {
          "1:6.18.39-1+rpt1": {
            "linux_commit": "60ea684a8ace97bb0db1a16e20753bdd6ab371ff",
            "upstream_version": "6.18.39",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.18.50"
          }
        }
      }
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-89768"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/88c927a63dc717b6d46b20fe13ea713916e49089"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c03114634d342648bd34910aa8fb88007e92cc3c"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/a35cc21355734e1acb89973d9be90ca8e4c3ed2f"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-09-11T19:47:07Z"
  }
}