[CVE-2026-72046][MODERATE 7.0] gve: fix header buffer corruption with header-split and HW-GRO [ Upstream commit d676c9a73bdcd8237425dbb826f2bd1a25c36e40 ]

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

CVE: CVE-2026-72046
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: gve: fix header buffer corruption with header-split and HW-GRO [ Upstream commit d676c9a73bdcd8237425dbb826f2bd1a25c36e40 ]
Commit: 84d3753d4bf284ef770ead6dee2270aaabb3ef41
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=84d3753d4bf284ef770ead6dee2270aaabb3ef41
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72046
Analysis date: Sat, 15 Aug 2026 05:18:37 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
The gve DQO RX path can corrupt packet headers when header-split and HW-GRO are enabled because header buffers are indexed by queue position instead of buffer identity, allowing network traffic with out-of-order completions to cause retransmissions and network DoS.

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

The original Linux kernel CVE announcement for CVE-2026-72046 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72046

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
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CVE-2026-72046	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H';CWE-362;*CWE-664;CWE-345;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.9';DESCR 'gve DQO RX with header split and HW GRO can copy packet headers from the wrong header buffer slot because the post path indexes header buffers by queue position while the receive completion path reads them by completion index. With multiple flows and out of order completions this can mix headers between packets or reuse a header slot while the device may still write to it. For the CVSS the PR:N is used for the paranoid score because a sender does not need local code execution on the victim and only needs network reachability to the affected gve interface under the required offload configuration. The issue is network traffic reachable but depends on specific Google virtual NIC features and traffic patterns, so AC:H is appropriate. Impact is mainly packet corruption and denial of service through retransmissions or degraded throughput, with no strong evidence of kernel memory corruption or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-72046 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 5e37d8254e7f551dda62e7590e819d69c7491845 YES  NO NO unknown 	MAYBE	REMOTE READ OOB DANGER INIT NETWORK SKB TIMER HARDWARE LINUS KPANIC MEMORY PACKET 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

This is not a strong Important candidate by itself because the patch does not show UAF, OOB write into arbitrary kernel objects, privilege escalation, info leak, or kernel crash. It is still actionable because it is network-traffic-influenced and involves DMA-backed RX header buffer corruption in a real packet-processing path.

## 2. Signal breakdown

Paranoid scoring:

* Remote reachable / network-triggerable: +2
  Incoming traffic can influence the affected RX path when the host uses gve DQO RX with header-split and HW-GRO enabled.

* Constrained kernel buffer overwrite / corruption: +1
  The corruption is limited to driver-managed header buffers. The target is bounded and tied to RX buffer slots, not an arbitrary kernel address.

* Real lifetime / ownership corruption: +1
  The driver may re-post a header buffer slot while the device can still write to it, which is an ownership/lifetime mismatch between driver and device.

* Availability impact realistic: +1
  The commit reports about 30 percent throughput loss and many TCP retransmissions. This supports real network DoS or degradation.

* Hard or configuration-specific trigger: -1
  Triggering requires gve, DQO RX, header-split, HW-GRO, multiple flows, and out-of-order completion behavior.

Conservative score uses the same reasoning but treats reachability as less universal because the bug depends on a specific Google NIC driver and offload configuration.

Not awarded:

* No strong generic memory corruption +2 because the patch does not show arbitrary write, heap overwrite, UAF reclaim, type confusion, or attacker-selected kernel object corruption.
* No privilege escalation plausible signal because there is no demonstrated path from packet header mixup to kernel control or credential modification.
* No confidentiality impact because the patch does not show a read-back or information disclosure primitive.

## 3. Reachability analysis

A remote or adjacent network sender may trigger the issue by generating traffic patterns that exercise HW-GRO with multiple flows on an affected gve interface. The attacker does not need local code execution on the victim, but the target must use the Google gve driver with DQO RX, header-split, and HW-GRO enabled. This is more realistic in Google Cloud or similar environments using gve than on general Linux systems.

Namespaces and containers do not meaningfully reduce the attacker requirement if the trigger is external packet traffic. However, local configuration of the NIC features is privileged and normally controlled by the host administrator.

Call-site confidence: high. The patch shows both relevant call paths: buffer posting in `gve_rx_post_buffers_dqo()` and header copy on completion in `gve_rx_dqo()`.

## 4. Severity interpretation

This behaves like an actionable Moderate issue. The realistic impact is packet/header corruption, TCP retransmissions, and degraded network availability. The theoretical concern is that DMA-backed buffer ownership is mishandled, but the patch context supports constrained RX header buffer corruption rather than a general kernel memory corruption or LPE primitive.

Manual review is justified because network traffic can influence the bug and because device DMA buffer lifetime mistakes are easy to underestimate. Still, without evidence of arbitrary memory corruption, this should not be promoted to Important solely from the provided patch.

## 5. One-sentence report phrase

The gve DQO RX path can corrupt packet headers when header-split and HW-GRO are enabled because header buffers are indexed by queue position instead of buffer identity, allowing network traffic with out-of-order completions to cause retransmissions and network DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-triggerable RX data-path corruption plus DMA-backed buffer ownership mismatch warrants manual review, even though the likely impact is constrained network DoS rather than privilege escalation.

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

Patch: gve: fix header buffer corruption with header-split and HW-GRO [ Upstream commit d676c9a73bdcd8237425dbb826f2bd1a25c36e40 ]
Commit: 84d3753d4bf284ef770ead6dee2270aaabb3ef41
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=84d3753d4bf284ef770ead6dee2270aaabb3ef41

Commit description:

The DQO RX datapath programs a per-buffer-queue-descriptor
header_buf_addr at post time and reads the split header back at
completion time. Both the post and the read currently index the
header buffer by queue position rather than by the buffer's identity:

  - post (gve_rx_post_buffers_dqo): header_buf_addr is computed from
    bufq->tail
  - read (gve_rx_dqo): the header is read from desc_idx (the completion
    queue head index)

This relies on the buffer-queue index and the completion-queue index
being equal for the start of every packet, i.e. on the device consuming
posted buffers and returning completions in the exact same order. That
assumption does not hold once HW-GRO is enabled with multiple
flows: coalesced segments are accepted and completed in an order that
may differ from the order buffers were posted, and segments from
different flows may interleave.

That results in two problems:

1. Wrong header slot on read. Because the read offset is derived from
   the completion index (desc_idx) while the device wrote the header to
   the address programmed for the buffer's buf_id, the driver can copy
   a header belonging to a different packet. This shows up as
   throughput drop (about 30% drop and large numbers of TCP
   retransmissions) with header-split and HW-GRO both enabled and many
   streams.

2. Header buffer reused while still owned by the device. The driver
   advances bufq->head by one per completion and re-posts buffers based
   on that. Arrival of N RX completions only guarantees that at least N
   RX buffer descriptors have been read by the device. It does not
   guarantee that the device has relinquished the ownership of all the
   buffers corresponding to those N descriptors. With out-of-order
   completions (e.g. the completion for a packet copied into buffer N
   arrives before the completion for a packet copied into buffer N-1),
   the driver can re-post and overwrite a header buffer that the device
   is still going to write into, corrupting the header of a packet
   whose completion has not yet been processed.

Fix both issues by indexing the header buffer by buf_id on both the post
and read paths. Reading from buf_id's slot is therefore always correct
regardless of completion ordering (fixes problem 1).

Indexing by buf_id also ties each header slot to the lifetime of its
buffer state. A buffer state is only returned to the free/recycle lists
when its own completion (buf_id) is processed, so its header slot can
only be re-posted after the device is done with it. This makes header
slot reuse safe under out-of-order completions (fixes problem 2).

Allocate (gve_rx_alloc_hdr_bufs) and free (gve_rx_free_hdr_bufs) the
header buffers based on num_buf_states to match the buf_id indexing.

Cc: stable@vger.kernel.org
Fixes: 5e37d8254e7f ("gve: Add header split data path")
Signed-off-by: Ankit Garg <nktgrg@google.com>
Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Jordan Rhee <jordanrhee@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Signed-off-by: Joshua Washington <joshwash@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260617013208.3781453-1-joshwash@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- drivers/net/ethernet/google/gve/gve_rx_dqo.c 28

Changed files:
  drivers/net/ethernet/google/gve/gve_rx_dqo.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=84d3753d4bf284ef770ead6dee2270aaabb3ef41

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

The original Linux kernel CVE announcement for CVE-2026-72046 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72046

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 5.9

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: 4
  Paranoid ActionableScore: 5

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).