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CVE-2026-89840
f2fs: validate MOVE_RANGE destination size
Published 2026-09-16 (33 days ago) by the Linux kernel CNA. Subsystem fs/f2fs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89840 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixedDSA-6568-1 · 2026-10-16 · text | 6.12.113-1 | Update the kernel and reboot. DSA-6568-1 shipped the fix on 2026-10-16, in 6.12.113-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
F2FS_IOC_MOVE_RANGE checks the source range, but not the destination end before updating i_size. A source hole can expose this: __clone_blkaddrs() skips NULL_ADDR entries and returns success, so the caller can still extend the destination inode with unchecked pos_out + len. Reject destination overflow and use inode_newsize_ok() before extending the destination inode.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/f2fs/file.c
- What this is
- F2FS FILE SYSTEMMAINTAINERS section matched on fs/f2fs/ · linux-f2fs-devel@lists.sourceforge.net · Maintained
- Kernel module
- f2fs
Check it on the machine
grep -w CONFIG_F2FS_FS /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w f2fsPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookworm, trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_F2FS_FS
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-16 (33 days ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/f2fs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.8 | 6.12.112 | bca61ee5192e |
| 4.8 | 6.18.53 | db1306466952 |
| 4.8 | 7.2.5 | dcae1eeda531 |
| 4.8 | 7.3 | e533889fc26a |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DSA-6568-1 | 2026-10-16 | trixie 6.12.113-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- F2FS_IOC_MOVE_RANGE is a local ioctl (f2fs_ioctl → f2fs_ioc_move_range → f2fs_move_file_range) on f2fs file descriptors. f2fs has no remap_file_range, so nfsd/ksmbd copy_file_range cannot reach this path.
- AC:LAttack complexity, low
- The attacker fully controls pos_out and len and can ftruncate a sparse source so __clone_blkaddrs skips NULL_ADDR holes and returns success, making the unchecked destination i_size update deterministic with no race or uncontrollable layout.
- PR:LPrivileges required, low
- f2fs_ioc_move_range has no capable() check; it only needs FMODE_READ|FMODE_WRITE on the source and FMODE_WRITE on the destination. Any unprivileged user with files on mounted f2fs (Android /data, embedded userdata) can trigger it.
- UI:NUser interaction, none
- The attacker opens their own files on an already-mounted f2fs volume and issues F2FS_IOC_MOVE_RANGE; no separate victim action such as mounting a filesystem or opening a crafted file is required.
- S:UScope, unchanged
- Impact is corruption of f2fs inode size metadata and subsequent filesystem/kernel state on the local host, a standard kernel compromise within the same security authority with no VM escape or IOMMU bypass.
- C:NConfidentiality impact, none
- The bug writes an oversized or overflowed i_size; reads of the resulting sparse file return zeros or EOF (negative i_size makes pos >= i_size), and lookups beyond max_file_blocks fail with -E2BIG, so there is no kernel-memory or cross-file disclosure primitive.
- I:HIntegrity impact, high
- Missing overflow and inode_newsize_ok() checks let the attacker set destination i_size past s_maxbytes or wrap size_t into a negative loff_t, persisting corrupt on-disk inode size and poisoning later paths (fallocate COLLAPSE nrpages, __exchange_data_block ALLOC_NODE) that trust i_size for block-tree updates.
- A:HAvailability impact, high
- A poisoned i_size enables unbounded node-tree walks and block-exchange loops (SEEK_DATA/HOLE, fallocate COLLAPSE via DIV_ROUND_UP(i_size)), can hang the kernel or exhaust node space, and leaves durable filesystem corruption on shared f2fs userdata.