[CVE-2026-46279][LOW] mm/alloc_tag: clear codetag for pages allocated before page_ext initialization

[CVE-2026-46279][LOW] mm/alloc_tag: clear codetag for pages allocated before page_ext initialization

[AL-KERNEL]

CVE: CVE-2026-46279
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/alloc_tag: clear codetag for pages allocated before page_ext initialization
Commit: d5b495ba9de0423ef39f8bd86729a885870c7efe
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d5b495ba9de0423ef39f8bd86729a885870c7efe
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46279
Analysis date: Mon, 06 Jul 2026 20:25:42 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
Pages allocated before page_ext initialization may lack alloc_tag codetag metadata, causing a debug-only alloc_tag warning on later free paths, with practical impact limited to warning or panic_on_warn DoS in non-default debug configurations.

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

The original Linux kernel CVE announcement for CVE-2026-46279 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46279

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-2026-46279	LOW	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:N/I:N/A:H';CWE-665;CWE-703;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'Pages allocated before page_ext initialization can have no codetag reference, so later freeing them under CONFIG_MEM_ALLOC_PROFILING_DEBUG can trigger an alloc_tag warning. This is a debug configuration issue tied to early boot allocation ordering and later free paths, not a demonstrated UAF, OOB access, information leak, or arbitrary write primitive. For the CVSS the PR:L is used because practical triggering after boot requires a local process or user context that causes allocation and free activity, even though the root cause is created during boot. The issue is not network reachable. Impact is mainly a warning or low availability impact, with a paranoid A:H interpretation only for systems where panic_on_warn or similar debug policy turns the warning into a kernel crash.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) 	YES	OOB LOCK DISK INIT RACE LEAK UAF KERNEL_PANIC_PLUS_UAF HARDWARE LINUS MEMORY  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. After boot, ordinary local allocation/free activity can expose the warning path, although the root cause is created during early boot initialization.
* WARN/state validation concern: +1. The observed failure mode is `WARN_ONCE("alloc_tag was not set")` due to an uninitialized codetag reference.
* Rare/non-default configuration: -1. The warning is explicitly limited to `CONFIG_MEM_ALLOC_PROFILING_DEBUG=Y` with `mem_profiling_compressed` disabled, and the trace also involves KASAN quarantine behavior.

Paranoid-only signal:

* Reliable kernel crash / strong DoS: +1. Only defensible for systems configured with `panic_on_warn` or equivalent debug policy, where this warning becomes a host crash.

Not applied:

* No generic memory corruption. The patch does not show UAF, double free, OOB write, arbitrary write, type confusion, or attacker-controlled reclaim.
* No privilege escalation plausible. The codetag state is accounting/debug metadata, not a demonstrated control or data corruption primitive.
* No confidentiality or integrity impact. There is no read-back, disclosure path, writable stale object access, or protected data modification.
* No network reachability.

Call-site confidence: high. The patch includes the relevant allocation tagging path, the later tag lookup behavior, the early PFN tracking logic, and the warning trace.

## 3. Reachability analysis

The issue is created during early boot because some pages are allocated before `page_ext` and page allocation tagging metadata are fully initialized. A later local process can trigger allocation/free activity that causes these pages to be freed through KASAN-related paths and hits the alloc tag warning. This is not remotely reachable and does not depend on packet input or network protocol parsing.

Namespaces and containers do not materially improve reachability beyond ordinary local execution, because the affected condition is global kernel boot-time/debug metadata state. The path is not default-enabled in normal production kernels because it requires `CONFIG_MEM_ALLOC_PROFILING_DEBUG=Y` and `mem_profiling_compressed` disabled.

## 4. Severity interpretation

This behaves like a Low-like or ordinary Moderate debug-configuration warning, not an Important-class vulnerability. The realistic impact is a kernel warning. The paranoid impact is a kernel crash only on systems where warnings are configured to panic. There is no supported evidence of exploitable memory corruption, privilege escalation, or sensitive data exposure.

## 5. One-sentence report phrase

Pages allocated before page_ext initialization may lack alloc_tag codetag metadata, causing a debug-only alloc_tag warning on later free paths, with practical impact limited to warning or panic_on_warn DoS in non-default debug configurations.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for security triage unless the evaluated product intentionally ships `CONFIG_MEM_ALLOC_PROFILING_DEBUG=Y` with `panic_on_warn` in production.

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

Patch: mm/alloc_tag: clear codetag for pages allocated before page_ext initialization
Commit: d5b495ba9de0423ef39f8bd86729a885870c7efe
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d5b495ba9de0423ef39f8bd86729a885870c7efe

Commit description:

Due to initialization ordering, page_ext is allocated and initialized
relatively late during boot.  Some pages have already been allocated and
freed before page_ext becomes available, leaving their codetag
uninitialized.

A clear example is in init_section_page_ext(): alloc_page_ext() calls
kmemleak_alloc().  If the slab cache has no free objects, it falls back to
the buddy allocator to allocate memory.  However, at this point page_ext
is not yet fully initialized, so these newly allocated pages have no
codetag set.  These pages may later be reclaimed by KASAN, which causes
the warning to trigger when they are freed because their codetag ref is
still empty.

Use a global array to track pages allocated before page_ext is fully
initialized.  The array size is fixed at 8192 entries, and will emit a
warning if this limit is exceeded.  When page_ext initialization
completes, set their codetag to empty to avoid warnings when they are
freed later.

This warning is only observed with CONFIG_MEM_ALLOC_PROFILING_DEBUG=Y and
mem_profiling_compressed disabled:

[    9.582133] ------------[ cut here ]------------
[    9.582137] alloc_tag was not set
[    9.582139] WARNING: ./include/linux/alloc_tag.h:164 at __pgalloc_tag_sub+0x40f/0x550, CPU#5: systemd/1
[    9.582190] CPU: 5 UID: 0 PID: 1 Comm: systemd Not tainted 7.0.0-rc4 #1 PREEMPT(lazy)
[    9.582192] Hardware name: Red Hat KVM, BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[    9.582194] RIP: 0010:__pgalloc_tag_sub+0x40f/0x550
[    9.582196] Code: 00 00 4c 29 e5 48 8b 05 1f 88 56 05 48 8d 4c ad 00 48 8d 2c c8 e9 87 fd ff ff 0f 0b 0f 0b e9 f3 fe ff ff 48 8d 3d 61 2f ed 03 <67> 48 0f b9 3a e9 b3 fd ff ff 0f 0b eb e4 e8 5e cd 14 02 4c 89 c7
[    9.582197] RSP: 0018:ffffc9000001f940 EFLAGS: 00010246
[    9.582200] RAX: dffffc0000000000 RBX: 1ffff92000003f2b RCX: 1ffff110200d806c
[    9.582201] RDX: ffff8881006c0360 RSI: 0000000000000004 RDI: ffffffff9bc7b460
[    9.582202] RBP: 0000000000000000 R08: 0000000000000000 R09: fffffbfff3a62324
[    9.582203] R10: ffffffff9d311923 R11: 0000000000000000 R12: ffffea0004001b00
[    9.582204] R13: 0000000000002000 R14: ffffea0000000000 R15: ffff8881006c0360
[    9.582206] FS:  00007ffbbcf2d940(0000) GS:ffff888450479000(0000) knlGS:0000000000000000
[    9.582208] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    9.582210] CR2: 000055ee3aa260d0 CR3: 0000000148b67005 CR4: 0000000000770ef0
[    9.582211] PKRU: 55555554
[    9.582212] Call Trace:
[    9.582213]  <TASK>
[    9.582214]  ? __pfx___pgalloc_tag_sub+0x10/0x10
[    9.582216]  ? check_bytes_and_report+0x68/0x140
[    9.582219]  __free_frozen_pages+0x2e4/0x1150
[    9.582221]  ? __free_slab+0xc2/0x2b0
[    9.582224]  qlist_free_all+0x4c/0xf0
[    9.582227]  kasan_quarantine_reduce+0x15d/0x180
[    9.582229]  __kasan_slab_alloc+0x69/0x90
[    9.582232]  kmem_cache_alloc_noprof+0x14a/0x500
[    9.582234]  do_getname+0x96/0x310
[    9.582237]  do_readlinkat+0x91/0x2f0
[    9.582239]  ? __pfx_do_readlinkat+0x10/0x10
[    9.582240]  ? get_random_bytes_user+0x1df/0x2c0
[    9.582244]  __x64_sys_readlinkat+0x96/0x100
[    9.582246]  do_syscall_64+0xce/0x650
[    9.582250]  ? __x64_sys_getrandom+0x13a/0x1e0
[    9.582252]  ? __pfx___x64_sys_getrandom+0x10/0x10
[    9.582254]  ? do_syscall_64+0x114/0x650
[    9.582255]  ? ksys_read+0xfc/0x1d0
[    9.582258]  ? __pfx_ksys_read+0x10/0x10
[    9.582260]  ? do_syscall_64+0x114/0x650
[    9.582262]  ? do_syscall_64+0x114/0x650
[    9.582264]  ? __pfx_fput_close_sync+0x10/0x10
[    9.582266]  ? file_close_fd_locked+0x178/0x2a0
[    9.582268]  ? __x64_sys_faccessat2+0x96/0x100
[    9.582269]  ? __x64_sys_close+0x7d/0xd0
[    9.582271]  ? do_syscall_64+0x114/0x650
[    9.582273]  ? do_syscall_64+0x114/0x650
[    9.582275]  ? clear_bhb_loop+0x50/0xa0
[    9.582277]  ? clear_bhb_loop+0x50/0xa0
[    9.582279]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[    9.582280] RIP: 0033:0x7ffbbda345ee
[    9.582282] Code: 0f 1f 40 00 48 8b 15 29 38 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff c3 0f 1f 40 00 f3 0f 1e fa 49 89 ca b8 0b 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d fa 37 0d 00 f7 d8 64 89 01 48
[    9.582284] RSP: 002b:00007ffe2ad8de58 EFLAGS: 00000202 ORIG_RAX: 000000000000010b
[    9.582286] RAX: ffffffffffffffda RBX: 000055ee3aa25570 RCX: 00007ffbbda345ee
[    9.582287] RDX: 000055ee3aa25570 RSI: 00007ffe2ad8dee0 RDI: 00000000ffffff9c
[    9.582288] RBP: 0000000000001000 R08: 0000000000000003 R09: 0000000000001001
[    9.582289] R10: 0000000000001000 R11: 0000000000000202 R12: 0000000000000033
[    9.582290] R13: 00007ffe2ad8dee0 R14: 00000000ffffff9c R15: 00007ffe2ad8deb0
[    9.582292]  </TASK>

[Commit description truncated; see the upstream URL below]

Changed files:
  include/linux/alloc_tag.h
  include/linux/pgalloc_tag.h
  lib/alloc_tag.c
  mm/page_alloc.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=d5b495ba9de0423ef39f8bd86729a885870c7efe

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

The original Linux kernel CVE announcement for CVE-2026-46279 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46279

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 1
  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).