[CVE-2026-46106][MODERATE 7.0] eventfs: Hold eventfs_mutex and SRCU when remount walks events

[CVE-2026-46106][MODERATE 7.0] eventfs: Hold eventfs_mutex and SRCU when remount walks events

[AL-KERNEL]

CVE: CVE-2026-46106
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: eventfs: Hold eventfs_mutex and SRCU when remount walks events
Commit: ae9cd0b46b1890040006a2fc5e905c5d6053fd02
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae9cd0b46b1890040006a2fc5e905c5d6053fd02
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46106
Analysis date: Thu, 28 May 2026 19:31:07 -0400
ActionableScore: 7
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in tracefs eventfs remount handling can walk eventfs children after SRCU protected eventfs_inodes are removed or reclaimed, causing LIST_POISON dereference or a UAF candidate and making this a local DoS with possible memory corruption impact.

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

The original Linux kernel CVE announcement for CVE-2026-46106 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46106

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: MODERATE 7.0
Manual review required: YES

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

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

CVE-2026-46106	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in tracefs eventfs remount handling can let tracefs_apply_options walk eventfs children while eventfs_remove_rec removes entries and frees eventfs_inodes through SRCU. The old path only used rcu_read_lock, which does not protect objects freed by eventfs_srcu, and it also allowed concurrent writes to ei attr against eventfs_set_attr. A local attacker who can remount /sys/kernel/tracing and modify kprobe_events can race remount against event removal, causing LIST_POISON dereference or a use-after-free candidate. For the CVSS the PR:L paranoid case is used because delegated tracefs remount or tracing control can exist for a local service account or container root, while the base case remains PR:H on normal systems. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) 	MAYBE	LOCK DISK TRACE RACE UAF LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid score signals:

* Local lower privilege trigger: +1. A non full root local actor may be relevant if tracefs remount or tracing controls are delegated to a service account, container root, or reduced capability environment.
* Generic memory corruption: +2. The patch context explicitly says eventfs_inodes may be reclaimed under the walk because rcu_read_lock does not protect SRCU freed objects.
* Real lifetime corruption: +1. This is an SRCU lifetime bug with possible stale ti private or eventfs_inode access.
* Reliable kernel crash / strong DoS: +1. The commit describes LIST_POISON1 dereference and provides a reproducer racing remount with kprobe_events creation and deletion.
* Weak LPE concern: +1. UAF candidate plus concurrent writes to ei attr justify manual review, but no reliable reclaim or overwrite primitive is demonstrated.
* Confidentiality impact plausible: +1. Only for paranoid triage because UAF class can sometimes expose stale object state.
* Integrity impact plausible: +1. Only for paranoid triage because racing writes to freed or stale eventfs objects may corrupt state.
* Hard or unreliable race: -1. Trigger requires timing between tracefs remount walking eventfs and event removal.

Conservative score signals:

* Generic memory corruption: +2.
* Real lifetime corruption: +1.
* Reliable kernel crash / strong DoS: +1.
* Hard race: -1.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Normal remount of /sys/kernel/tracing and kprobe_events manipulation are privileged.

## 3. Reachability analysis

The direct trigger is local. A reproducer needs one actor repeatedly remounting /sys/kernel/tracing while another creates and removes kprobe events. On typical systems this requires root or CAP_SYS_ADMIN plus tracing privileges, so the conservative score is low borderline. However, tracefs and tracing controls are sometimes exposed to privileged containers, debugging services, CI agents, or reduced capability service accounts. In those cases PR:L is defensible for paranoid triage. The path is not network reachable. The issue is realistic as a crash because the commit provides a concrete race reproducer and names LIST_POISON1 dereference and SRCU lifetime mismatch.

## 4. Severity interpretation

This is not an ordinary resource leak or warning cleanup. It is a race plus SRCU lifetime bug with a UAF candidate. Realistically demonstrated impact is local kernel crash / DoS. Theoretical memory corruption impact is plausible because an eventfs object can be reclaimed while being walked and attributes can be written without the eventfs_mutex contract. No strong LPE primitive such as controlled reclaim, arbitrary write, or object replacement is demonstrated, so the main risk should be treated as actionable Moderate with Important candidate handling rather than confirmed Important exploitation.

## 5. One-sentence report phrase

A race in tracefs eventfs remount handling can walk eventfs children after SRCU protected eventfs_inodes are removed or reclaimed, causing LIST_POISON dereference or a UAF candidate and making this a local DoS with possible memory corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a race involving SRCU lifetime mismatch and a UAF candidate, with a concrete crash reproducer and possible memory corruption beyond a simple NULL dereference.

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

Patch: eventfs: Hold eventfs_mutex and SRCU when remount walks events
Commit: ae9cd0b46b1890040006a2fc5e905c5d6053fd02
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae9cd0b46b1890040006a2fc5e905c5d6053fd02

Commit description:

Commit 340f0c7 ("eventfs: Update all the eventfs_inodes from the
events descriptor") had eventfs_set_attrs() recurse through ei->children
on remount.  The walk only holds the rcu_read_lock() taken by
tracefs_apply_options() over tracefs_inodes, which is wrong:

  - list_for_each_entry over ei->children races with the list_del_rcu()
    in eventfs_remove_rec() -- LIST_POISON1 deref, same shape as
    d260327 .
  - eventfs_inodes are freed via call_srcu(&eventfs_srcu, ...).
    rcu_read_lock() does not extend an SRCU grace period, so ti->private
    can be reclaimed under the walk.
  - The writes to ei->attr race with eventfs_set_attr(), which holds
    eventfs_mutex.

Reproducer:

  while :; do mount -o remount,uid=$((RANDOM%1000)) /sys/kernel/tracing; done &
  while :; do
      echo "p:kp submit_bio" > /sys/kernel/tracing/kprobe_events
      echo > /sys/kernel/tracing/kprobe_events
  done

Wrap the events portion of tracefs_apply_options() in
eventfs_remount_lock()/_unlock() that take eventfs_mutex and
srcu_read_lock(&eventfs_srcu).  eventfs_set_attrs() doesn't sleep so the
nested rcu_read_lock() is fine; lockdep_assert_held() pins the contract.

Comment in tracefs_drop_inode() said "RCU cycle" -- it is SRCU.

Fixes: 340f0c7 ("eventfs: Update all the eventfs_inodes from the events descriptor")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260418191737.10289-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/tracefs/event_inode.c
  fs/tracefs/inode.c
  fs/tracefs/internal.h

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=ae9cd0b46b1890040006a2fc5e905c5d6053fd02

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

The original Linux kernel CVE announcement for CVE-2026-46106 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46106

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:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 3
  Paranoid ActionableScore: 7

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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).