[CVE-2026-46002][LOW] ext2: reject inodes with zero i_nlink and valid mode in ext2_iget()

[CVE-2026-46002][LOW] ext2: reject inodes with zero i_nlink and valid mode in ext2_iget()

[AL-KERNEL]

CVE: CVE-2026-46002
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ext2: reject inodes with zero i_nlink and valid mode in ext2_iget()
Commit: 32e0b925572686399243834ec99e2a9d85c62eae
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=32e0b925572686399243834ec99e2a9d85c62eae
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46002
Analysis date: Wed, 27 May 2026 17:18:33 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-46002 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46002

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-46002	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-20;CWE-754;CWE-617;*CWE-664;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'ext2_iget() could accept a corrupted inode with i_nlink equal to 0, a valid mode, and no deletion time, allowing it to reach VFS unlink rename or rmdir paths. A crafted ext2 image can then trigger WARN_ON in drop_nlink() when those operations decrement an already zero link count. For the CVSS the PR:L is used in the paranoid score because a local user may trigger the operation once the crafted filesystem is mounted, although mounting such an image normally requires administrator privileges. The issue is not network reachable and does not provide a memory corruption primitive. Impact is denial of service through WARN or panic_on_warn, not information disclosure or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-46002  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DISK WARNONLY HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=2
ActionableScoreLower=0

1. ActionableScore
* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Availability impact realistic: +1. A crafted ext2 image can trigger `WARN_ON` in `drop_nlink()`, and systems with `panic_on_warn` may turn this into DoS.
* Important filesystem/storage path: +1. The bug is in ext2 inode loading and VFS name operation paths.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Creating the vulnerable state usually requires mounting a crafted ext2 filesystem image, which normally requires administrator privileges.
* Paranoid local trigger: +1. If the crafted filesystem is already mounted by an administrator, a local user with access to that tree may trigger unlink, rename, or rmdir.
* Rare/configuration-dependent exposure: -1. This requires a corrupted or crafted ext2 image with a specific invalid inode state.
* No memory corruption signal. The patch shows WARN/consistency failure, not UAF, OOB write, arbitrary write, info leak, or LPE.

3. Reachability analysis
The primary attacker model is a crafted ext2 filesystem image mounted on the victim. Mounting such an image normally requires root or `CAP_SYS_ADMIN`, so ordinary users usually cannot set up the vulnerable state. Once mounted, local users with access to the affected inode may trigger the WARN through unlink, rename, or rmdir. The issue is not network reachable and containers only matter if they are allowed to mount or access attacker-controlled ext2 images.

4. Severity interpretation
This behaves like a Low-like malformed filesystem DoS issue. The realistic impact is WARN or `panic_on_warn` triggered by corrupted inode metadata reaching VFS operations. There is no demonstrated memory corruption, confidentiality impact, integrity impact beyond malformed filesystem state, or privilege escalation.

5. One-sentence report phrase
A crafted ext2 image with an inode having zero `i_nlink`, valid mode, and no deletion time can reach VFS unlink or rename paths and trigger `drop_nlink()` WARN-based DoS.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This is a crafted-filesystem WARN/DoS issue that typically requires privileged mount and does not show memory corruption or privilege escalation.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: ext2: reject inodes with zero i_nlink and valid mode in ext2_iget()
Commit: 32e0b925572686399243834ec99e2a9d85c62eae
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=32e0b925572686399243834ec99e2a9d85c62eae

Commit description:

ext2_iget() already rejects inodes with i_nlink == 0 when i_mode is
zero or i_dtime is set, treating them as deleted. However, the case of
i_nlink == 0 with a non-zero mode and zero dtime slips through. Since
ext2 has no orphan list, such a combination can only result from
filesystem corruption - a legitimate inode deletion always sets either
i_dtime or clears i_mode before freeing the inode.

A crafted image can exploit this gap to present such an inode to the
VFS, which then triggers WARN_ON inside drop_nlink() (fs/inode.c) via
ext2_unlink(), ext2_rename() and ext2_rmdir():

WARNING: CPU: 3 PID: 609 at fs/inode.c:336 drop_nlink+0xad/0xd0 fs/inode.c:336
CPU: 3 UID: 0 PID: 609 Comm: syz-executor Not tainted 6.12.77+ #1
Call Trace:
 <TASK>
 inode_dec_link_count include/linux/fs.h:2518 [inline]
 ext2_unlink+0x26c/0x300 fs/ext2/namei.c:295
 vfs_unlink+0x2fc/0x9b0 fs/namei.c:4477
 do_unlinkat+0x53e/0x730 fs/namei.c:4541
 __x64_sys_unlink+0xc6/0x110 fs/namei.c:4587
 do_syscall_64+0xf5/0x220 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

WARNING: CPU: 0 PID: 646 at fs/inode.c:336 drop_nlink+0xad/0xd0 fs/inode.c:336
CPU: 0 UID: 0 PID: 646 Comm: syz.0.17 Not tainted 6.12.77+ #1
Call Trace:
 <TASK>
 inode_dec_link_count include/linux/fs.h:2518 [inline]
 ext2_rename+0x35e/0x850 fs/ext2/namei.c:374
 vfs_rename+0xf2f/0x2060 fs/namei.c:5021
 do_renameat2+0xbe2/0xd50 fs/namei.c:5178
 __x64_sys_rename+0x7e/0xa0 fs/namei.c:5223
 do_syscall_64+0xf5/0x220 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

WARNING: CPU: 0 PID: 634 at fs/inode.c:336 drop_nlink+0xad/0xd0 fs/inode.c:336
CPU: 0 UID: 0 PID: 634 Comm: syz-executor Not tainted 6.12.77+ #1
Call Trace:
 <TASK>
 inode_dec_link_count include/linux/fs.h:2518 [inline]
 ext2_rmdir+0xca/0x110 fs/ext2/namei.c:311
 vfs_rmdir+0x204/0x690 fs/namei.c:4348
 do_rmdir+0x372/0x3e0 fs/namei.c:4407
 __x64_sys_unlinkat+0xf0/0x130 fs/namei.c:4577
 do_syscall_64+0xf5/0x220 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
 </TASK>

Extend the existing i_nlink == 0 check to also catch this case,
reporting the corruption via ext2_error() and returning -EFSCORRUPTED.
This rejects the inode at load time and prevents it from reaching any
of the namei.c paths.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
Link: https://patch.msgid.link/20260404152011.2590197-1-kovalev@altlinux.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/inode.c
  include/linux/fs.h
  fs/ext2/namei.c
  fs/namei.c
  arch/x86/entry/common.c
  fs/ext2/inode.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=32e0b925572686399243834ec99e2a9d85c62eae

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-46002 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46002

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 0
  Paranoid ActionableScore: 2

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).