[CVE-2026-74479][MODERATE REGULAR] net: pktgen: fix proc entry use-after-free

[CVE-2026-74479][MODERATE REGULAR] net: pktgen: fix proc entry use-after-free

[AL-KERNEL]

CVE: CVE-2026-74479
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: pktgen: fix proc entry use-after-free
Commit: 4ef801b838d85c0ea5852c50667f7344ce3b6cd0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ef801b838d85c0ea5852c50667f7344ce3b6cd0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74479
Analysis date: Sat, 15 Aug 2026 14:33:37 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race between pktgen device rename and removal can pass a stale `proc_dir_entry` pointer to `proc_remove()`, causing a kernel use-after-free and likely local DoS, with limited but nonzero privilege-escalation concern in delegated CAP_NET_ADMIN environments.

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

The original Linux kernel CVE announcement for CVE-2026-74479 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74479

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 REGULAR
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-2026-74479	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-416;CWE-362;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 'pktgen has a race between NETDEV_CHANGENAME handling and kpktgend device removal where proc_remove can receive a stale proc_dir_entry pointer. The stale entry may already have been freed by the rename path, causing a slab use-after-free in proc_remove and a kernel crash. For the CVSS the PR:L is used in the paranoid score because reliable triggering may be possible for a local actor with delegated network administration or pktgen control rather than full host root in some deployments. The issue is not directly network reachable and is triggered through local pktgen and netdev control plane operations. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use-after-free, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 3)	YES	REMOTE READ OOB DANGER RACE UAF HARDWARE LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* +1 Memory corruption, weak primitive: confirmed race-dependent slab use-after-free of `proc_dir_entry` in `proc_remove()`.
* +1 Real lifetime corruption: stale procfs entry pointer can survive concurrent rename/removal.
* +1 Reliable kernel crash / strong DoS: KASAN reports UAF in `proc_remove()`, and a normal kernel may crash or oops.
* -1 Hard or unreliable race: triggering depends on timing between `NETDEV_CHANGENAME` and `kpktgend` removal.
* -2 Requires admin/root/CAP_NET_ADMIN in typical deployments: pktgen and netdev rename/removal are normally privileged control-plane operations.

Paranoid adjustments:

* +1 Weak LPE concern: because this is a kernel heap UAF involving a procfs object passed into a removal/lifetime-management path, stale-object reuse should be manually reviewed, although no controlled reclaim or write primitive is demonstrated.
* Privilege penalty is relaxed in the paranoid view because CAP_NET_ADMIN or pktgen control may be delegated to containers or reduced-capability service contexts and may not always mean full host root.

Race-UAF downgrade applied: this is not treated as a strong corruption primitive because the patch does not show attacker-controlled reclaim, write-after-free, type confusion, callback control, or refcount takeover.

## 3. Reachability analysis

The bug is locally triggerable through pktgen and netdev control-plane operations, not through incoming network traffic. In typical deployments, writing to pktgen control interfaces and renaming/removing network devices requires root or CAP_NET_ADMIN, so the conservative score is low. In containerized or delegated network-administration environments, the effective privilege may be closer to PR:L because a reduced-capability actor may control network devices or pktgen without being full host root. pktgen is not a common default data-plane path and is mostly a testing or traffic-generation facility, which limits exposure.

Call-site confidence: high, because the patch directly shows `proc_remove(pkt_dev->entry)` being moved under `if_lock()` and the commit provides the exact racing call paths.

## 4. Severity interpretation

This behaves more like a borderline but actionable Moderate than a clear Important issue. The realistic demonstrated impact is local DoS via kernel crash. The theoretical concern is higher because the primitive is a real kernel heap use-after-free, but there is no evidence in the patch of controlled object replacement, arbitrary write, callback hijack, or reliable privilege escalation. Manual review is still required because early triage should not auto-close confirmed kernel UAF races.

## 5. One-sentence report phrase

A race between pktgen device rename and removal can pass a stale `proc_dir_entry` pointer to `proc_remove()`, causing a kernel use-after-free and likely local DoS, with limited but nonzero privilege-escalation concern in delegated CAP_NET_ADMIN environments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed kernel heap use-after-free in a lifetime-management path. Even though the practical impact appears to be local DoS and triggering is privileged/timing-dependent, UAF cases should not be auto-closed without manual validation of reclaim and privilege-boundary scenarios.

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

Patch: net: pktgen: fix proc entry use-after-free
Commit: 4ef801b838d85c0ea5852c50667f7344ce3b6cd0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ef801b838d85c0ea5852c50667f7344ce3b6cd0

Commit description:

pktgen_change_name() replaces pkt_dev->entry while holding t->if_lock.
pktgen_remove_device() removes the same entry before
_rem_dev_from_if_list() takes that lock.

This allows the following interleaving:

  CPU 0 (NETDEV_CHANGENAME)       CPU 1 (kpktgend)
  if_lock(t)
  proc_remove(pkt_dev->entry)
                                  proc_remove(pkt_dev->entry)
  pkt_dev->entry = proc_create_data(...)
  if_unlock(t)

The kthread can pass the stale proc_dir_entry to proc_remove() after the
rename path has freed it. A reproducer with a widened race window reports:

  BUG: KASAN: slab-use-after-free in proc_remove+0x78/0x80
  Read of size 8 at addr ffff8881478fea70 by task kpktgend_0/67
  Call Trace:
   proc_remove+0x78/0x80
   pktgen_remove_device.isra.0+0x11c/0x4c0
   pktgen_thread_worker+0x1214/0x6bc0
   kthread+0x2c6/0x3b0
  Allocated by task 95:
   __proc_create+0x204/0x790
   proc_create_data+0x72/0xe0
   pktgen_thread_write+0xd61/0x1510
  Freed by task 28:
   kmem_cache_free+0xcb/0x3d0
   proc_free_inode+0x5b/0x80
   rcu_core+0x50a/0x1850
  The buggy address belongs to the object at ffff8881478fea00
   which belongs to the cache proc_dir_entry of size 192

Move proc_remove() into the if_lock-protected list removal helper. Keep it
before list_del_rcu() to preserve the ordering required by add_device().
The rename path must then finish replacing the entry before removal, or
it observes that the device is no longer on the list.

Fixes: 39df232 ("[PKTGEN]: fix device name handling")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260719145740.2888967-1-nicoyip.dev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/core/pktgen.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=4ef801b838d85c0ea5852c50667f7344ce3b6cd0

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

The original Linux kernel CVE announcement for CVE-2026-74479 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74479

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: 2
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).