[CVE-2026-46331][IMPORTANT] net/sched: fix pedit partial COW leading to page cache corruption tcf_pedit_act() computes the COW range for skb_ensure_writable() once before the key loop using tcfp_off_max_hint, but the hint does not account for the runtime header offset added by typed keys. This can leave part of the write region un-COW'd. Fix by moving skb_ensure_writable() inside the per-key loop where the actual write offset is known, and add overflow checking on the offset arithmetic. For negative offsets (e.g. Ethernet header edits at ingress), use skb_cow() to COW the headroom instead. Guard offset_valid() against INT_MIN, where negation is undefined. Fixes: 8b79647 ("net/sched: act_pedit: really ensure the skb is writable") Reported-by: Yiming Qian <yimingqian591@gmail.com> Reported-by: Keenan Dong <keenanat2000@gmail.com> Reported-by: Han Guidong <2045gemini@gmail.com> Reported-by: Zhang Cen <rollkingzzc@gmail.com> Reviewed-by: Han Guidong <2045gemini@gmail.com> Tested-by: Han Guidong <2045gemini@gmail.com> Reviewed-by: Davide Caratti <dcaratti@redhat.com> Tested-by: Davide Caratti <dcaratti@redhat.com> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com> Tested-by: Toke Høiland-Jørgensen <toke@redhat.com> Reviewed-by: Victor Nogueira <victor@mojatatu.com> Tested-by: Victor Nogueira <victor@mojatatu.com> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com> Signed-off-by: Rajat Gupta <rajat.gupta@oss.qualcomm.com> Link: https://patch.msgid.link/20260531123221.48732-1-jhs@mojatatu.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-46331
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net/sched: fix pedit partial COW leading to page cache corruption tcf_pedit_act() computes the COW range for skb_ensure_writable() once before the key loop using tcfp_off_max_hint, but the hint does not account for the runtime header offset added by typed keys. This can leave part of the write region un-COW'd. Fix by moving skb_ensure_writable() inside the per-key loop where the actual write offset is known, and add overflow checking on the offset arithmetic. For negative offsets (e.g. Ethernet header edits at ingress), use skb_cow() to COW the headroom instead. Guard offset_valid() against INT_MIN, where negation is undefined. Fixes: 8b79647 ("net/sched: act_pedit: really ensure the skb is writable") Reported-by: Yiming Qian <yimingqian591@gmail.com> Reported-by: Keenan Dong <keenanat2000@gmail.com> Reported-by: Han Guidong <2045gemini@gmail.com> Reported-by: Zhang Cen <rollkingzzc@gmail.com> Reviewed-by: Han Guidong <2045gemini@gmail.com> Tested-by: Han Guidong <2045gemini@gmail.com> Reviewed-by: Davide Caratti <dcaratti@redhat.com> Tested-by: Davide Caratti <dcaratti@redhat.com> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com> Tested-by: Toke Høiland-Jørgensen <toke@redhat.com> Reviewed-by: Victor Nogueira <victor@mojatatu.com> Tested-by: Victor Nogueira <victor@mojatatu.com> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com> Signed-off-by: Rajat Gupta <rajat.gupta@oss.qualcomm.com> Link: https://patch.msgid.link/20260531123221.48732-1-jhs@mojatatu.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Commit: 899ee91156e57784090c5565e4f31bd7dbffbc5a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=899ee91156e57784090c5565e4f31bd7dbffbc5a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46331
Analysis date: Tue, 16 Jun 2026 02:51:39 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
`tc pedit can corrupt shared or file backed skb memory because the writable COW range was computed before the actual per key write offset was known, making this an actionable page cache corruption issue that usually requires CAP_NET_ADMIN or delegated tc control to trigger.`

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

The original Linux kernel CVE announcement for CVE-2026-46331 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46331

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: IMPORTANT
Manual review required: YES

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

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

CVE-2026-46331	IMPORTANT	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-668;*CWE-664;*CWE-787;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H';BEST CVSS score: '7';DESCR 'tc pedit can corrupt shared skb backing memory because tcf_pedit_act computed the writable COW range once before the key loop and did not include the runtime header offset used by typed keys. As a result a later per key write may modify bytes that were not made private, which can lead to page cache corruption when the skb references shared or file backed pages. For the CVSS the PR:L value is used for the paranoid score because reliable triggering normally requires a local user or container service with delegated CAP_NET_ADMIN or equivalent tc rule control rather than full host root. The issue is not directly network reachable as a pure remote packet bug, although packets can exercise the vulnerable action after such traffic control rules are installed. Impact is at least denial of service and integrity corruption, and the page cache corruption primitive makes privilege escalation plausible enough for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE OOB DANGER SKB IPV6 KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	NO	NO	guess

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* **Memory corruption, strong corruption primitive: +2**
  The commit explicitly describes partial COW failure leading to **page cache corruption**, not just a crash or warning.

* **Dirty-Pipe-like ownership/COW violation: +2**
  The bug allows `tcf_pedit_act()` to write into skb-backed memory that was not made private by `skb_ensure_writable()`. This resembles a COW ownership violation where shared or file-backed memory may be modified unexpectedly.

* **Integrity impact plausible: +1**
  Page cache corruption can affect data integrity and may bypass expected write permissions or object ownership assumptions.

* **Availability impact realistic: +1**
  Corrupting shared skb/page-cache backing memory can plausibly cause crashes, data corruption, or unstable kernel behavior.

* **Important filesystem/storage/page-cache path: +1**
  The impact involves page-cache-backed data, which is a high-value kernel memory and storage integrity boundary.

* **Requires CAP_NET_ADMIN in typical deployments: -2 conservative / -1 paranoid**
  Installing `tc pedit` actions normally requires `CAP_NET_ADMIN`. However, container or namespace delegation can make this reachable to reduced-privilege actors, so the paranoid score uses a smaller penalty.

## 3. Reachability analysis

The bug is triggered through the traffic-control `pedit` action in `net/sched`. Reliable setup normally requires the ability to configure tc rules, typically `CAP_NET_ADMIN`, so this is not a pure remote network-triggered vulnerability. After a vulnerable rule is installed, packet traffic can exercise the affected data path.

Namespaces matter: a container root or delegated service with `CAP_NET_ADMIN` in a network namespace may be able to configure the action without having full host root. This makes `PR:L` a defensible paranoid interpretation for practical triage, even though many host deployments restrict tc administration to privileged users.

The affected subsystem is not a default packet path for all systems, but `net/sched` and tc are common Linux networking components. The key risk is not broad remote exposure, but the **page-cache/COW corruption primitive** once the action is reachable.

## 4. Severity interpretation

This is stronger than an ordinary Moderate DoS issue because the patch and commit message identify **page cache corruption** from an incomplete COW operation. The realistic exploitation evidence does not prove arbitrary code execution, but it does support a meaningful integrity-impact primitive and possible privilege-boundary consequences.

Conservatively this is an **Actionable Moderate** that should not be auto-closed. Paranoid triage reasonably treats it as a **Strong Important candidate**, because page-cache corruption and COW bypass patterns have historically produced underestimated privilege and integrity impact.

## 5. One-sentence report phrase

`tc pedit can corrupt shared or file backed skb memory because the writable COW range was computed before the actual per key write offset was known, making this an actionable page cache corruption issue that usually requires CAP_NET_ADMIN or delegated tc control to trigger.`

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Manual review is required because the issue is explicitly page-cache/COW corruption, not a simple bounds-checking or DoS-only fix. The main open question is how controllable the corrupted bytes and backing pages are under realistic tc and skb construction conditions.

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

Patch: net/sched: fix pedit partial COW leading to page cache corruption tcf_pedit_act() computes the COW range for skb_ensure_writable() once before the key loop using tcfp_off_max_hint, but the hint does not account for the runtime header offset added by typed keys. This can leave part of the write region un-COW'd. Fix by moving skb_ensure_writable() inside the per-key loop where the actual write offset is known, and add overflow checking on the offset arithmetic. For negative offsets (e.g. Ethernet header edits at ingress), use skb_cow() to COW the headroom instead. Guard offset_valid() against INT_MIN, where negation is undefined. Fixes: 8b79647 ("net/sched: act_pedit: really ensure the skb is writable") Reported-by: Yiming Qian <yimingqian591@gmail.com> Reported-by: Keenan Dong <keenanat2000@gmail.com> Reported-by: Han Guidong <2045gemini@gmail.com> Reported-by: Zhang Cen <rollkingzzc@gmail.com> Reviewed-by: Han Guidong <2045gemini@gmail.com> Tested-by: Han Guidong <2045gemini@gmail.com> Reviewed-by: Davide Caratti <dcaratti@redhat.com> Tested-by: Davide Caratti <dcaratti@redhat.com> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com> Tested-by: Toke Høiland-Jørgensen <toke@redhat.com> Reviewed-by: Victor Nogueira <victor@mojatatu.com> Tested-by: Victor Nogueira <victor@mojatatu.com> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com> Signed-off-by: Rajat Gupta <rajat.gupta@oss.qualcomm.com> Link: https://patch.msgid.link/20260531123221.48732-1-jhs@mojatatu.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Commit: 899ee91156e57784090c5565e4f31bd7dbffbc5a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=899ee91156e57784090c5565e4f31bd7dbffbc5a

Changed files:
  include/net/tc_act/tc_pedit.h
  net/sched/act_pedit.c
  net/ipv6.h
  net/netlink.h
  net/pkt_sched.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=899ee91156e57784090c5565e4f31bd7dbffbc5a

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

The original Linux kernel CVE announcement for CVE-2026-46331 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46331

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:L/UI:N/S:U/C:L/I:H/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: 6
  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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).