[CVE-2026-98511][MODERATE REGULAR] drm/nouveau: don't bump pin count on failed re-pin in nouveau_bo_pin_locked()

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

CVE: CVE-2026-98511
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/nouveau: don't bump pin count on failed re-pin in nouveau_bo_pin_locked()
Commit: a6e755acf85793a7b4d29ba27b5421af1087263f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a6e755acf85793a7b4d29ba27b5421af1087263f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98511
Analysis date: Sun, 18 Oct 2026 23:22:26 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A failed incompatible Nouveau BO re-pin incorrectly increments the TTM pin count without a matching unpin, causing invalid resource accounting and a later kernel warning but no established memory corruption, privilege escalation, or host-wide denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-98511 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98511

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: NO

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

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

CVE-2026-98511	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98511 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE RESULT=SAME V39_AEGIS_ONE_STEP_UP=LOW->MODERATE (final reconciliation agrees; DECISION: both MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';CWE-911;CWE-703;*CWE-772;BEST CVSS score: '3.3';DESCR 'nouveau_bo_pin_locked can increment the TTM buffer object pin count even after determining that an existing placement is incompatible with a new pin request and returning EBUSY. Callers treat the failed operation as if no pin was acquired, so no matching unpin occurs and ttm_bo_release later detects a nonzero pin count. For the CVSS the PR:L value is used because a local process must have access to the nouveau DRM device and issue a suitable sequence of buffer object operations. The issue is not network reachable. The demonstrated impact is incorrect GPU resource accounting and a kernel warning, with possible limited resource retention. There is no supported UAF, OOB access, information disclosure, arbitrary write, kernel panic, or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 3.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to MODERATE because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Concrete resource and accounting retention. `ttm_bo_pin()` increments `bo->pin_count` after the domain compatibility check has already failed with `-EBUSY`. The caller therefore performs no matching unpin, leaving the BO pinned longer than intended.
* +0 WARN consequence. `WARN_ON_ONCE(bo->pin_count)` is demonstrated, but no kernel panic, host-wide resource exhaustion, or persistent failure after BO destruction is established.
* +0 Memory corruption. No OOB read or write, UAF, double release, stale pointer, invalid free, or attacker-directed overwrite is present.
* +0 Authorization impact. No security check changes from DENY to ALLOW.
* +0 B5-R. There is no retry-accumulated heap OOB write or later consumption of corrupted descriptors.
* +0 V33 or V34. Although `pin_count` is active BO state, no checksum corruption, privileged downstream packet consumer, or guest or namespace trust-boundary chain exists.
* No privilege penalty was applied because the supplied UID 0 Syzkaller reproducer does not establish that host-admin privileges are required.
* No local-unprivileged bonus was awarded because access to the complete vulnerable Nouveau operation through a render node or another below-admin interface is not established.

3. Reachability analysis

The trigger is local and requires an open Nouveau DRM device plus a sequence that pins a BO and then requests an incompatible memory domain. The supplied reproducer ran as UID 0, but that does not prove UID 0 or effective host-administrator powers are required.

Ordinary logged-in user, render-node, DRM-master, compositor, delegated graphics service, and host-administrator reachability cannot be distinguished from the supplied call trace. The vulnerable operation may be reachable through a delegated DRM file descriptor, but the complete below-host-admin path is not shown. Therefore `HostAdminRequired` and namespace-scoped reachability remain unknown.

A Nouveau-backed GPU or emulated test device is required. This is hardware-specific but not sufficient for a rare-hardware penalty. The defect is deterministic and does not require a race or narrow timing window.

4. Primitive and severity interpretation

The exact primitive is an unmatched increment of a live TTM BO pin counter after a failed re-pin request. This creates invalid active-object accounting and may retain the BO placement until final object cleanup. It is not a stale-object or post-lifetime operation.

There is no first release that can end the BO lifetime followed by a second operation through the same dangling reference. Consequently, the concrete repeated-release signal does not apply, the UAF floors do not apply, and `RealUAF=NO`.

The demonstrated consequence is a kernel warning during `ttm_bo_release()` and possible limited GPU resource retention. Host-wide exhaustion is unresolved and not sufficiently supported to score an additional availability effect. Confidentiality, protected-state integrity, privilege escalation, and remote reachability are not established.

`PrimitiveClass=CLASS_C` because the demonstrated behavior is invalid bookkeeping and WARN-level cleanup behavior without an independently useful corruption primitive. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` because no memory-corruption, ownership, authorization, or trust-boundary mechanism remains unresolved.

5. One-sentence report phrase

A failed incompatible Nouveau BO re-pin incorrectly increments the TTM pin count without a matching unpin, causing invalid resource accounting and a later kernel warning but no established memory corruption, privilege escalation, or host-wide denial of service.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a deterministic pin-accounting mismatch only, with no B5-R OOB write, UAF, authorization bypass, protected-resource impact, or credible Important-preserving primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/nouveau: don't bump pin count on failed re-pin in nouveau_bo_pin_locked()
Commit: a6e755acf85793a7b4d29ba27b5421af1087263f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a6e755acf85793a7b4d29ba27b5421af1087263f

Commit description:

nouveau_bo_pin_locked() checks whether an already pinned BO is in a
memory domain compatible with a new pin request. When the domains are
incompatible, it sets -EBUSY but still calls ttm_bo_pin() before
returning.

Callers treat a failed nouveau_bo_pin() as not having acquired a new pin,
so the extra pin count is never decreased by a matching unpin.
This triggers the warning in ttm_bo_release():

	WARN_ON_ONCE(bo->pin_count);

Found when fuzzing the nouveau driver with a modified Syzkaller:

	WARNING: drivers/gpu/drm/ttm/ttm_bo.c:256 at ttm_bo_release+0x827/0x9e0 drivers/gpu/drm/ttm/ttm_bo.c:256, CPU#1: syz.3.24/2212
	Modules linked in:
	CPU: 1 UID: 0 PID: 2212 Comm: syz.3.24 Not tainted 7.2.0 #24 PREEMPT(lazy)
	nouveau 0000:01:00.0: gsp:msg fn:103 len:0x40/0x20 res:0x19 resp:0x19
	Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
	RIP: 0010:ttm_bo_release+0x827/0x9e0 drivers/gpu/drm/ttm/ttm_bo.c:256
	Code: 02 00 0f 85 51 01 00 00 48 8b 7b 08 e8 d2 20 01 00 e9 80 fd ff ff e8 d8 15 c0 fe 90 0f 0b 90 e9 e1 f8 ff ff e8 ca 15 c0 fe 90 <0f> 0b 90 e9 a4 f8 ff ff e8 bc 15 c0 fe be 03 00 00 00 4c 89 e7 e8
	msg: 00000000: 05 00 d0 c1 04 00 f0 f1 01 30 00 00 2d 90 00 00  .........0..-...
	RSP: 0018:ffffc9000f5cf710 EFLAGS: 00010293
	RAX: 0000000000000000 RBX: ffff888018e5d2a8 RCX: ffffffff82bb1b36
	RDX: ffff888017b68000 RSI: 0000000000000004 RDI: ffff888018e5d2a8
	msg: 00000010: 19 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	RBP: ffff88801261c720 R08: 0000000000000001 R09: ffffed10031cba55
	R10: ffff888018e5d2ab R11: 00000000000000f3 R12: ffff888018e5d290
	R13: ffff888018e5d2d4 R14: ffff88801b219c18 R15: dffffc0000000000
	FS:  0000000000000000(0000) GS:ffff8880e0f6f000(0000) knlGS:0000000000000000
	CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
	CR2: 0000001b31223ffc CR3: 0000000028e00005 CR4: 0000000000770ef0
	PKRU: 80000000
	Call Trace:
	<TASK>
	kref_put include/linux/kref.h:65 [inline]
	ttm_bo_put drivers/gpu/drm/ttm/ttm_bo.c:325 [inline]
	ttm_bo_fini+0x55/0x80 drivers/gpu/drm/ttm/ttm_bo.c:330
	nouveau_gem_object_del+0xb2/0x1b0 drivers/gpu/drm/nouveau/nouveau_gem.c:90
	drm_gem_object_free+0x5f/0x90 drivers/gpu/drm/drm_gem.c:1165
	kref_put include/linux/kref.h:65 [inline]
	__drm_gem_object_put include/drm/drm_gem.h:562 [inline]
	drm_gem_object_put include/drm/drm_gem.h:575 [inline]
	nouveau_abi16_chan_fini.constprop.0+0x44f/0x5a0 drivers/gpu/drm/nouveau/nouveau_abi16.c:195
	nouveau 0000:01:00.0: syz.2.23[2209]: Unknown handle 0x00000000
	nouveau_abi16_fini+0x1d0/0x340 drivers/gpu/drm/nouveau/nouveau_abi16.c:225
	nouveau_drm_postclose+0x18b/0x3e0 drivers/gpu/drm/nouveau/nouveau_drm.c:1284
	nouveau 0000:01:00.0: syz.2.23[2209]: validate_init
	drm_file_free.part.0+0x6d6/0xb60 drivers/gpu/drm/drm_file.c:267
	drm_file_free drivers/gpu/drm/drm_file.c:237 [inline]
	drm_close_helper.isra.0+0x11a/0x160 drivers/gpu/drm/drm_file.c:290
	drm_release+0x1ab/0x330 drivers/gpu/drm/drm_file.c:438
	__fput+0x39c/0xa60 fs/file_table.c:512
	nouveau 0000:01:00.0: syz.2.23[2209]: validate: -2
	task_work_run+0x15a/0x230 kernel/task_work.c:233
	exit_task_work include/linux/task_work.h:40 [inline]
	do_exit+0x82b/0x25a0 kernel/exit.c:1009
	do_group_exit+0xc2/0x280 kernel/exit.c:1152
	get_signal+0x1d6e/0x1f30 kernel/signal.c:3046
	arch_do_signal_or_restart+0x7d/0x6e0 arch/x86/kernel/signal.c:337
	__exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
	exit_to_user_mode_loop+0xdf/0x440 kernel/entry/common.c:101
	__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
	syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
	syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
	do_syscall_64+0x4f8/0x690 arch/x86/entry/syscall_64.c:100
	entry_SYSCALL_64_after_hwframe+0x77/0x7f
	RIP: 0033:0x7f12bac8594d
	Code: Unable to access opcode bytes at 0x7f12bac85923.
	RSP: 002b:00007f12b96e70d8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
	RAX: 0000000000000001 RBX: 00007f12baf15fa8 RCX: 00007f12bac8594d
	RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f12baf15fac
	RBP: 00007f12baf15fa0 R08: 00007f12baee8000 R09: 0000000000000000
	R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
	R13: 00007f12baf16038 R14: 0000000000000006 R15: 00007ffe2ed394b0
	</TASK>
	irq event stamp: 47867
	hardirqs last  enabled at (47883): [<ffffffff815cafc6>] __up_console_sem+0x66/0x70 kernel/printk/printk.c:347
	hardirqs last disabled at (47892): [<ffffffff815cafab>] __up_console_sem+0x4b/0x70 kernel/printk/printk.c:345
	softirqs last  enabled at (47880): [<ffffffff81434277>] __do_softirq kernel/softirq.c:656 [inline]
	softirqs last  enabled at (47880): [<ffffffff81434277>] invoke_softirq kernel/softirq.c:496 [inline]

[Commit description truncated; see the upstream URL below]

Changed files:
  drivers/gpu/drm/ttm/ttm_bo.c
  include/linux/kref.h
  drivers/gpu/drm/nouveau/nouveau_gem.c
  drivers/gpu/drm/drm_gem.c
  include/drm/drm_gem.h
  drivers/gpu/drm/nouveau/nouveau_abi16.c
  drivers/gpu/drm/nouveau/nouveau_drm.c
  drivers/gpu/drm/drm_file.c
  fs/file_table.c
  kernel/task_work.c
  include/linux/task_work.h
  kernel/exit.c
  kernel/signal.c
  arch/x86/kernel/signal.c
  kernel/entry/common.c
  include/linux/irq-entry-common.h
  include/linux/entry-common.h
  arch/x86/entry/syscall_64.c
  kernel/printk/printk.c
  kernel/softirq.c
  drivers/gpu/drm/nouveau/nouveau_bo.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=a6e755acf85793a7b4d29ba27b5421af1087263f

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

The original Linux kernel CVE announcement for CVE-2026-98511 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98511

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 3.3

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: unknown
  Paranoid ActionableScore: 1

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).