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CVE-2026-63812
f2fs: fix incorrect FI_NO_EXTENT handling in __destroy_extent_node()
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs/f2fs. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-63812 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixed | 6.12.95-1 | Update the kernel and reboot. Fixed in 6.12.95-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.3-1 | Update the kernel and reboot. Fixed in 7.1.3-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
When __destroy_extent_node() sets the inode flag FI_NO_EXTENT, it does not reset the length of the largest extent to 0 and update the inode folio. Since modifications to the extent tree are disallowed afterward, the cached largest extent may become stale. This can trigger the following error in xfstests generic/388: F2FS-fs (dm-0): sanity_check_extent_cache: inode (ino=1761) extent info [220057, 57, 6] is incorrect, run fsck to fix In the f2fs_drop_inode path, __destroy_extent_node() does not need to guarantee that et->node_cnt is 0, because concurrency with writeback is expected in this path, and writeback may update the extent cache. This patch reverts commit ed78aeebef05 ("f2fs: fix node_cnt race between extent node destroy and writeback"), and remove the unnecessary zero check of et->node_cnt.
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/extent_cache.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
- 2026-07-19 (3 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.6.140 | 6.6.144 | 7e4d8f98be63 |
| 6.12.88 | 6.12.95 | 58a5deb220bc |
| 6.18.30 | 6.18.38 | 20190e498057 |
| 7.1 | 7.1.3 | edf12cbeeeab |
| 7.1 | 7.2 | 1f70ddb28a3c |
| 7.0.7 | 0 | 0 |
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
- The bug is reached only through local VFS filesystem activity (write, unlink, concurrent writeback) on an F2FS mount, most severely on Android/embedded userdata partitions where F2FS is the default local filesystem.
- AC:LAttack complexity, low
- An attacker can reliably orchestrate the inode-eviction/writeback race by unlinking files while writeback is in progress on the same inode, controlling both sides of the concurrency window.
- PR:LPrivileges required, low
- Triggering the race requires only unprivileged write access to files on a mounted F2FS filesystem (e.g., creating, writing, and unlinking files in one's own directory on Android /data), not real root or CAP_SYS_ADMIN.
- UI:NUser interaction, none
- Exploitation requires no action from a separate victim; the attacker drives the file I/O and unlink operations that provoke the stale extent-cache state.
- S:UScope, unchanged
- Impact is confined to kernel/filesystem integrity on the affected host; there is no cross-security-authority boundary such as VM escape or container-to-host breakout.
- C:HConfidentiality impact, high
- Stale largest-extent metadata persisted to the on-disk inode can cause subsequent reads (after inode reload or inode-number reuse) to map logical file offsets to wrong physical blocks, disclosing data from other files or freed blocks.
- I:HIntegrity impact, high
- Incorrect on-disk extent metadata corrupts the inode-to-block mapping and can cause wrong data blocks to be associated with a file, constituting exploitable filesystem metadata corruption with integrity impact beyond a simple crash.
- A:HAvailability impact, high
- The stale cache triggers sanity_check_extent_cache failures (as seen in xfstests generic/388), f2fs_handle_error(ERROR_CORRUPTED_INODE), and potential kernel BUG_ON via f2fs_bug_on when CONFIG_F2FS_CHECK_FS is enabled, all causing denial of filesystem or kernel service.