[CVE-2026-74393][MODERATE REGULAR] drm/syncobj: Fix memory leak in drm_syncobj_find_fence() [ Upstream

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

CVE: CVE-2026-74393
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/syncobj: Fix memory leak in drm_syncobj_find_fence() [ Upstream
Commit: e245f3491bf30a758786a4424854f61fee472308
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e245f3491bf30a758786a4424854f61fee472308
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74393
Analysis date: Sat, 15 Aug 2026 23:33:53 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Low-like. Not an Important candidate
Manual review required: NO

Summary:
A local DRM user can trigger a syncobj reference leak in `drm_syncobj_find_fence()` by passing invalid wait flags after a valid syncobj lookup, potentially causing gradual resource exhaustion DoS but not memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-74393 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74393

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.

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

CVE-2026-74393	MODERATE	CHECK WITH IMPACT FROM ORIG NN 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:H';*CWE-772;*CWE-401;CWE-404;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A reference leak in drm_syncobj_find_fence can occur when a valid syncobj is found and invalid wait flags are rejected on an early error path without dropping the syncobj reference. A local process with access to the DRM device node can repeat this path to keep syncobj objects pinned after they should be released, causing gradual kernel resource exhaustion. For the CVSS the PR:L is selected because triggering requires local code execution with access to a DRM file descriptor and syncobj handle, but it does not require full administrative privileges in common render node configurations. The issue is not network reachable. Impact is denial of service through memory or object lifetime exhaustion. There is no evidence of UAF, OOB access, arbitrary write, information disclosure, or privilege escalation from this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Not an Important candidate (with actual score 3)  SKIP CVE-2026-74393 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 18226ba52159257d4c2f777a168cc09adb3c1ac0 YES  NO NO unknown 	MAYBE	DEADLOCK SIMPLEFIX LEAK HARDWARE 	-	-	checked

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

ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Ordinary Moderate / Low-like. Not an Important candidate**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local process with access to a DRM device node and a valid syncobj handle can reach `drm_syncobj_find_fence()`.

* Real lifetime corruption: +1
  The bug is a reference lifetime leak. `drm_syncobj_find()` takes a reference and the invalid flags error path returned without dropping it.

Paranoid additional signals:

* Availability impact realistic: +1
  Repeated triggering can keep syncobj objects pinned and may cause gradual kernel memory or object lifetime exhaustion.

* Broad or common subsystem exposure: +1
  DRM syncobj APIs are common on systems with GPU render nodes, especially desktop, graphics, and compute workloads.

Signals not awarded:

* No remote reachable signal. This is not network-triggerable.
* No generic memory corruption signal. The patch shows a reference leak, not UAF, double-free, OOB write, or type confusion.
* No privilege escalation signal. There is no reclaim, overwrite, callback control, refcount takeover, or arbitrary write primitive.
* No confidentiality or integrity impact. The leak does not expose data or modify protected objects.

## 3. Reachability analysis

The bug is reachable by a local process that can open a DRM device and use syncobj ioctls. In common render-node configurations this may be available to unprivileged local users in the appropriate device access group, so PR:L is the practical interpretation. It is not reachable over the network.

Namespaces and containers may matter only if the DRM device is passed through or exposed to the container. Without device access, a containerized process cannot normally trigger it. The affected path is not a default network service and requires local DRM API access plus repeated calls to make resource exhaustion meaningful.

Call-site confidence: high. The provided patch shows the relevant early return path and the fix routes it through cleanup.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource exhaustion issue rather than an Important-class kernel vulnerability. The theoretical worst case is local DoS by repeated reference leaks until kernel memory or DRM objects are exhausted. Realistic exploitation evidence supports resource exhaustion only.

There is no supported memory corruption primitive, no UAF, no attacker-controlled reclaim, no arbitrary write, and no security-boundary bypass. The paranoid score is elevated only to keep sustained local resource exhaustion visible for triage, not because privilege escalation is plausible.

## 5. One-sentence report phrase

A local DRM user can trigger a syncobj reference leak in `drm_syncobj_find_fence()` by passing invalid wait flags after a valid syncobj lookup, potentially causing gradual resource exhaustion DoS but not memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a straightforward reference leak with local-only reachability and no evidence of UAF, OOB access, arbitrary write, information disclosure, or privilege escalation.

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

Patch: drm/syncobj: Fix memory leak in drm_syncobj_find_fence() [ Upstream
Commit: e245f3491bf30a758786a4424854f61fee472308
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e245f3491bf30a758786a4424854f61fee472308

Changed files:
  drivers/gpu/drm/drm_syncobj.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=e245f3491bf30a758786a4424854f61fee472308

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

The original Linux kernel CVE announcement for CVE-2026-74393 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74393

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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).