[CVE-2026-53210][LOW] tee: shm: fix shm leak in register_shm_helper()

[CVE-2026-53210][LOW] tee: shm: fix shm leak in register_shm_helper()

[AL-KERNEL]

CVE: CVE-2026-53210
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: tee: shm: fix shm leak in register_shm_helper()
Commit: 4277759906b44d923a38c8f59f5576501b187b0d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4277759906b44d923a38c8f59f5576501b187b0d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53210
Analysis date: Fri, 26 Jun 2026 03:18:49 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local process with access to the TEE device can trigger a small kernel memory leak by registering zero length shared memory, potentially causing resource exhaustion after repeated ioctl calls.

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

The original Linux kernel CVE announcement for CVE-2026-53210 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53210

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.

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

CVE-2026-53210	LOW	CHECK	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-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'register_shm_helper() in the TEE shared memory registration path allocates a shm object before calling iov_iter_npages(). If TEE_IOC_SHM_REGISTER is called with length 0, iov_iter_npages() returns 0 and the old error path drops the context reference but does not free the allocated shm object. A local process can repeat this ioctl on an accessible TEE device to leak small kernel allocations and eventually cause memory pressure or resource exhaustion. For the CVSS the PR:L because the attacker must be able to execute local code and access the TEE device file, but no administrative control is required if the device permissions allow the ioctl. The issue is not network reachable. Impact is denial of service only and no UAF, OOB access, information leak, or privilege escalation primitive is shown by the code path.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-53210  SKIP The Fixes patch not applied yet, so unlikely that actual: 7bdee41575919773818e525ea19e54eb817770af YES  NO NO unknown 	MAYBE	INIT SIMPLEFIX LEAK  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

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

## 2. Signal breakdown

* Local unprivileged trigger: +1. A local process with access to the TEE device can call `TEE_IOC_SHM_REGISTER` with `length=0`.
* Availability impact realistic: +1 in paranoid scoring only. Repeated calls can leak small kernel allocations and may eventually create memory pressure.
* Rare AND configuration-dependent subsystem: -1 in conservative scoring. The issue requires TEE support and an accessible TEE device node.
* No generic memory corruption: +0. The patch shows a missing free on an error path, not UAF, double-free, OOB write, type confusion, or arbitrary write.
* No privilege escalation plausible: +0. There is no demonstrated reclaim primitive, object confusion, overwrite, or sensitive-object access.
* No remote reachability: +0. This is a local ioctl path, not a network-triggerable bug.

## 3. Reachability analysis

The bug is triggered locally through `TEE_IOC_SHM_REGISTER` with a zero-length registration request. The attacker needs local code execution and permission to open the relevant TEE device node. It does not require root if device permissions expose `/dev/tee*` to an unprivileged user or service, but on many systems access may be restricted. Containers only matter if the TEE device is passed through into the container. The path is not network reachable and is not a default universal kernel attack surface.

## 4. Severity interpretation

This behaves like a low-end Moderate resource leak, not an Important-class kernel vulnerability. The realistic impact is local DoS through repeated small memory leaks. The patch does not support memory corruption, information disclosure, privilege escalation, or a security-boundary bypass. The paranoid score only raises availability concern for sustained abuse, not for a stronger exploit primitive.

## 5. One-sentence report phrase

A local process with access to the TEE device can trigger a small kernel memory leak by registering zero length shared memory, potentially causing resource exhaustion after repeated ioctl calls.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for urgent triage purposes because it is a local resource leak without evidence of memory corruption, privilege escalation, sensitive data exposure, or network reachability.

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

Patch: tee: shm: fix shm leak in register_shm_helper()
Commit: 4277759906b44d923a38c8f59f5576501b187b0d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4277759906b44d923a38c8f59f5576501b187b0d

Commit description:

register_shm_helper() allocates shm before calling
iov_iter_npages(). If iov_iter_npages() returns 0, the function
jumps to err_ctx_put and leaks shm.

This can be triggered by TEE_IOC_SHM_REGISTER with
struct tee_ioctl_shm_register_data where length is 0.

Jump to err_free_shm instead.

Fixes: 7bdee41 ("tee: Use iov_iter to better support shared buffer registration")
Cc: stable@vger.kernel.org
Cc: lvc-project@linuxtesting.org
Signed-off-by: Georgiy Osokin <g.osokin@auroraos.dev>
Reviewed-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/tee/tee_shm.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=4277759906b44d923a38c8f59f5576501b187b0d

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

The original Linux kernel CVE announcement for CVE-2026-53210 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53210

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: 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).