From: AL-KERNEL <[email protected]>
To: [email protected]
Subject: [CVE-2026-68239][MODERATE 7.0] drm/ttm: Account for NULL and handle pages in ttm_pool_backup
Date: Mon, 10 Aug 2026 09:53:38 -0400 [thread overview]
Message-ID: <[email protected]> (raw)
CVE: CVE-2026-68239
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/ttm: Account for NULL and handle pages in ttm_pool_backup
Commit: 22aa7fb4e7d0b3ab41d1240ed743167980912970
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22aa7fb4e7d0b3ab41d1240ed743167980912970
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68239
Analysis date: Mon, 10 Aug 2026 09:53:38 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-68239 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68239
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-68239 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';**CWE-476;CWE-704;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A NULL pointer dereference or invalid struct page access in the DRM/TTM ttm_pool_backup() path can occur because entries in tt pages may be NULL or backup handle values, but the old code could pass them to set_pages_array_wb() or later memory cleanup logic as real pages. A local process that can use a DRM render node and create TTM buffer objects may be able to reach this path through GPU memory pressure and the shrinker, causing an oops in kswapd and a kernel crash (DoS). For the CVSS the PR:L is used because reliable triggering does not normally require full administrator privileges when unprivileged DRM render access is available, but it does require local code execution and access to the GPU device. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in the paranoid interpretation may allow limited confidentiality or integrity impact because encoded backup handles can be treated as struct page pointers in memory management paths.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) SKIP CVE-2026-68239 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: b63d715b8090aed48bdef5930625946fa4c0d324 YES NO NO unknown MAYBE NULLPTR HARDWARE MEMORY DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
1. **ActionableScore**
* Conservative score: **3**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::
ActionableScore=5
ActionableScoreLower=3
2. **Signal breakdown**
* **Local unprivileged trigger: +1**. A local process with access to DRM render nodes may create GPU buffer objects and contribute to memory pressure that reaches the TTM shrinker path.
* **Memory corruption, weak/indirect corruption candidate: +1**. The bug can treat `NULL` or encoded backup-handle entries as real `struct page` pointers. This is stronger than pure bookkeeping, but the patch does not show controlled overwrite, UAF reclaim, or arbitrary write.
* **Reliable kernel crash / strong DoS: +1**. The commit includes a concrete oops in `set_pages_array_wb()` through `ttm_pool_backup()` and `kswapd`.
* **Broad/common subsystem exposure: +1**. DRM/TTM GPU memory management is common on systems with modern GPUs, especially desktop, workstation, and accelerated compute systems.
* **Hard or special triggering conditions: -1**. Triggering appears to require a specific TTM backup/shrinker state with mixed real pages, `NULL` entries, and backup handles under memory pressure.
* **Paranoid only: Weak LPE concern: +1**. Encoded handles being interpreted as `struct page` pointers in page attribute or purge/free-adjacent paths is a plausible corruption sink, but no concrete exploitation primitive is demonstrated.
* **Paranoid only: Integrity impact plausible: +1**. The affected path touches page attributes and page lifecycle handling. This supports limited integrity concern for manual review, but not a strong Important score.
3. **Reachability analysis**
A realistic trigger requires local code execution plus access to the affected DRM device, typically via a render node or GPU device file. Full root privileges are not necessarily required on systems where unprivileged users are allowed GPU render access, but the attacker still needs local device access and a suitable GPU/driver configuration. Containers only matter if the DRM device is passed through or delegated into the container. The issue is not network reachable. The observed crash path runs through TTM/Xe shrinker activity under memory pressure, so exploitation is plausible but condition-dependent rather than a trivial syscall crash.
Call-site confidence: **high**, because the provided trace and patch show the concrete path through `ttm_bo_shrink()`, `xe_bo_shrink_purge()`, the shrinker, and `set_pages_array_wb()`.
4. **Severity interpretation**
Conservatively this behaves like a local Moderate DoS: the demonstrated impact is a kernel oops from invalid page handling. The paranoid interpretation is **Actionable Moderate** because this is not just a warning or resource leak. It is invalid `struct page` handling in a memory-management path, with encoded handle values potentially reaching page attribute or cleanup logic. It should not be promoted to Strong Important based only on the patch, because there is no shown UAF reclaim, attacker-controlled replacement, arbitrary write, callback control, or reliable privilege-escalation primitive.
5. **One-sentence report phrase**
`DRM/TTM ttm_pool_backup() could pass NULL or backup-handle entries as real pages into page attribute and cleanup paths, allowing a local GPU user under memory pressure to trigger a kernel crash and requiring manual review for possible weak memory-corruption impact.`
6. **Manual review recommendation**
**MANUAL CHECK REQUIRED**
Reason: this is an invalid page-pointer handling bug in a kernel memory-management path with a demonstrated crash and a plausible but unproven corruption angle. It should not be auto-closed as ordinary low-risk DoS.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: drm/ttm: Account for NULL and handle pages in ttm_pool_backup
Commit: 22aa7fb4e7d0b3ab41d1240ed743167980912970
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22aa7fb4e7d0b3ab41d1240ed743167980912970
Commit description:
Pages in ttm_pool_backup can be NULL or backup handles
(ttm_backup_page_ptr_is_handle()), neither of which can be passed to
set_pages_array_wb() or freed. Add a dedicated WB pass before the
dma/purge loop that walks allocations using the same i += num_pages
stride, skipping NULL and handle entries, and calls set_pages_array_wb()
once per contiguous run of real pages. Apply the same NULL/handle guard
to the dma/purge loop.
Fixes the following oops:
Oops: general protection fault, kernel NULL pointer dereference 0x0: 0000 [#1] SMP NOPTI
RIP: 0010:__cpa_process_fault+0xf8/0x770
RSP: 0018:ffffc90000a87718 EFLAGS: 00010287
RAX: 0000000000000000 RBX: ffffc90000a87868 RCX: 0000000000000000
RDX: 0000000000001000 RSI: 0005088000000000 RDI: ffffffff827c5f34
RBP: 0005088000000000 R08: ffffc90000a877cb R09: ffffc90000a877d0
R10: 0000000000000000 R11: 000000000000001b R12: 000ffffffffff000
R13: ffffc90000a87868 R14: ffffc90000a87868 R15: ffff88815b882ae0
FS: 0000000000000000(0000) GS:ffff8884ec840000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f930b844000 CR3: 000000000262e003 CR4: 0000000008f70ef0
PKRU: 55555554
Call Trace:
<TASK>
__change_page_attr_set_clr+0x989/0xe90
? __purge_vmap_area_lazy+0x6c/0x3a0
? _vm_unmap_aliases+0x250/0x2a0
set_pages_array_wb+0x7f/0x120
ttm_pool_backup+0x4c9/0x5b0 [ttm]
? dma_resv_wait_timeout+0x3b/0xf0
ttm_tt_backup+0x32/0x60 [ttm]
ttm_bo_shrink+0x66/0x110 [ttm]
xe_bo_shrink_purge+0x12b/0x1b0 [xe]
xe_bo_shrink+0xbb/0x270 [xe]
__xe_shrinker_walk+0xf7/0x160 [xe]
xe_shrinker_walk+0x9d/0xc0 [xe]
xe_shrinker_scan+0x11f/0x210 [xe]
do_shrink_slab+0x13b/0x270
shrink_slab+0xf1/0x400
shrink_node+0x352/0x8a0
balance_pgdat+0x32c/0x700
kswapd+0x205/0x2f0
? __pfx_autoremove_wake_function+0x10/0x10
? __pfx_kswapd+0x10/0x10
kthread+0xd1/0x110
? __pfx_kthread+0x10/0x10
ret_from_fork+0x1b1/0x200
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
Cc: Christian Koenig <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Matthew Auld <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Simona Vetter <[email protected]>
Cc: Thomas Hellström <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Fixes: b63d715 ("drm/ttm/pool, drm/ttm/tt: Provide a helper to shrink pages")
Cc: [email protected]
Assisted-by: GitHub_Copilot:claude-opus-4.8
Signed-off-by: Matthew Brost <[email protected]>
Reviewed-by: Thomas Hellström <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/gpu/drm/ttm/ttm_pool.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=22aa7fb4e7d0b3ab41d1240ed743167980912970
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-68239 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68239
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:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 5.8
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: 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: NO
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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