# CVE-2025-40025: f2fs: fix to do sanity check on node footer for non inode dnode

> A local attacker can cause a kernel panic in the f2fs filesystem by mounting a crafted image, leading to a denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Oct 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-40025, DEBIAN-CVE-2025-40025, GHSA-j968-frjr-f6j9, ROOT-OS-DEBIAN-11-CVE-2025-40025, ROOT-OS-DEBIAN-12-CVE-2025-40025, ROOT-OS-DEBIAN-13-CVE-2025-40025, ROOT-OS-UBUNTU-2204-CVE-2025-40025, ROOT-OS-UBUNTU-2404-CVE-2025-40025, UBUNTU-CVE-2025-40025

## What is CVE-2025-40025?

CVE-2025-40025 is a high-severity denial of service vulnerability in Linux, published on 28 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to do sanity check on node footer for non inode dnode

As syzbot reported below:

------------[ cut here ]------------
kernel BUG at fs/f2fs/file.c:1243!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5354 Comm: syz.0.0 Not tainted 6.17.0-rc1-syzkaller-00211-g90d970cade8e #0 PREEMPT(full)
RIP: 0010:f2fs_truncate_hole+0x69e/0x6c0 fs/f2fs/file.c:1243
Call Trace:
 <TASK>
 f2fs_punch_hole+0x2db/0x330 fs/f2fs/file.c:1306
 f2fs_fallocate+0x546/0x990 fs/f2fs/file.c:2018
 vfs_fallocate+0x666/0x7e0 fs/open.c:342
 ksys_fallocate fs/open.c:366 [inline]
 __do_sys_fallocate fs/open.c:371 [inline]
 __se_sys_fallocate fs/open.c:369 [inline]
 __x64_sys_fallocate+0xc0/0x110 fs/open.c:369
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1e65f8ebe9

w/ a fuzzed image, f2fs may encounter panic due to it detects inconsistent
truncation range in direct node in f2fs_truncate_hole().

The root cause is: a non-inode dnode may has the same footer.ino and
footer.nid, so the dnode will be parsed as an inode, then ADDRS_PER_PAGE()
may return wrong blkaddr count which may be 923 typically, by chance,
dn.ofs_in_node is equal to 923, then count can be calculated to 0 in below
statement, later it will trigger panic w/ f2fs_bug_on(, count == 0 || ...).

	count = min(end_offset - dn.ofs_in_node, pg_end - pg_start);

This patch introduces a new node_type NODE_TYPE_NON_INODE, then allowing
passing the new_type to sanity_check_node_footer in f2fs_get_node_folio()
to detect corruption that a non-inode dnode has the same footer.ino and
footer.nid.

Scripts to reproduce:
mkfs.f2fs -f /dev/vdb
mount /dev/vdb /mnt/f2fs
touch /mnt/f2fs/foo
touch /mnt/f2fs/bar
dd if=/dev/zero of=/mnt/f2fs/foo bs=1M count=8
umount /mnt/f2fs
inject.f2fs --node --mb i_nid --nid 4 --idx 0 --val 5 /dev/vdb
mount /dev/vdb /mnt/f2fs
xfs_io /mnt/f2fs/foo -c "fpunch 6984k 4k"

## Which versions are affected by CVE-2025-40025?


## How do I fix CVE-2025-40025?

Apply the vendor's patch.

## Is CVE-2025-40025 being exploited?

There is no known exploitation of CVE-2025-40025 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40025 and fix it if it is affected.

What it is: CVE-2025-40025 is a high-severity denial of service vulnerability in Linux, published on 28 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40025 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40025/ (Markdown: https://insights.sbomify.com/CVE-2025-40025/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40025
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40025
- OSV: https://osv.dev/vulnerability/CVE-2025-40025

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40025/
Summaries are generated and may contain mistakes; the official description above is the record.