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CVE-2026-89768— fs: fix user path of nested backing files

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Linux 内核中，以下漏洞已得到修复： 文件系统：修复嵌套 backing 文件（backing file）的用户路径 从 推导应存储在新 backing 文件中的路径。但当 本身就是一个 backing 文件时（例如在嵌套堆叠文件系统中，一个 overlayfs 的 lowerdir 是另一个 overlayfs 的 merged 目录），这种推导方式是不正确的。自提交 （“fs: 在 backing 文件的 f_path 中存储真实路径而非伪造路径”）之后，backing 文件的 保存的是中间层的真实路径

AI Predicted 1.0 Difficulty: Theoretical

Possible ATT&CK Techniques 2 AI

T1015 T1059.007 · JavaScript

Affected Version Matrix 16

VendorProduct Version RangeStatus
Linux Linux 5b6aa9a843205da92d860e5011a7b29062a76b8f< 88c927a63dc717b6d46b20fe13ea713916e49089 affected
5dfcb15974e7d0f96aca278dd9f1b85df91523ef< c03114634d342648bd34910aa8fb88007e92cc3c affected
6af36aeb147a06dea47c49859cd6ca5659aeb987< a35cc21355734e1acb89973d9be90ca8e4c3ed2f affected
6af36aeb147a06dea47c49859cd6ca5659aeb987< f2381b546e7e6a35c9fcee0d0ccb6c042a9aeb5d affected
41c5b269af8b1f0bffcab7766a793f294ae6764e affected
27e795afba0018b0ea9460dbad4bd706d1ba5ee0 affected
6.12.95< 6.12.109 affected
6.18.38< 6.18.50 affected
… +8 more rows
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I. Basic Information for CVE-2026-89768

Vulnerability Information
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Vulnerability Title
fs: fix user path of nested backing files
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 5b6aa9a843205da92d860e5011a7b29062a76b8f ~ 88c927a63dc717b6d46b20fe13ea713916e49089 -
Linux Linux 7.1 -

II. Public POCs for CVE-2026-89768

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III. Intelligence Information for CVE-2026-89768

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Other References for CVE-2026-89768 (4)

Same Patch Batch · Linux · 2026-09-11 · 431 CVEs total

CVE-2026-89491 ocfs2: cluster: don't sleep while holding o2hb_live_lock in o2hb_region_pin()
CVE-2026-89477 sctp: fix NULL deref on untransmitted RECONF completion
CVE-2026-89478 sctp: drop a chunk if its transport was removed
CVE-2026-89479 sctp: stop processing a packet once its association is deleted
CVE-2026-89480 nvme-tcp: reject a read that transferred too few bytes
CVE-2026-89482 nvme-tcp: do not accept C2HData based on blk_rq_payload_bytes() alone
CVE-2026-89481 nvme-tcp: fix host memory disclosure on R2T for a read command
CVE-2026-89483 nvme: zero the discard fallback page
CVE-2026-89484 lockd: fix NULL dereference on lockowner allocation failure
CVE-2026-89485 lockd: pin next file across nlm_inspect_file lock-drop
CVE-2026-89486 ipmi: Fix use-after-free of cmd_rcvr in _ipmi_destroy_user()
CVE-2026-89487 openvswitch: only skb_tx_error() a packet we are about to drop
CVE-2026-89488 openvswitch: Fix CT limit teardown use-after-free
CVE-2026-89489 openrisc: fix arbitrary kernel memory access via or1k_atomic syscall
CVE-2026-89500 ring-buffer: Make cpu_buffer::free_page a buffer_data_read_page
CVE-2026-89497 orangefs: skip leading spaces before parsing client debug masks
CVE-2026-89498 orangefs: fix double-free of trailer_buf on readdir copy failure
CVE-2026-89499 ring-buffer: Stop remote reader update when page swap fails
CVE-2026-89496 ocfs2: always run deallocs on copy-on-write completion
CVE-2026-89501 ring-buffer: Hold cpu_buffer::lock when resizing a subbuf

Showing top 20 of 431 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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