[CVE-2026-64409][MODERATE REGULAR] Bluetooth: btmtksdio: fix infinite loop in btmtksdio_txrx_work()

[CVE-2026-64409][MODERATE REGULAR] Bluetooth: btmtksdio: fix infinite loop in btmtksdio_txrx_work()

[AL-KERNEL]

CVE: CVE-2026-64409
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: btmtksdio: fix infinite loop in btmtksdio_txrx_work()
Commit: f6682c23b6fac4780d297ae4662053d17e58fd52
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6682c23b6fac4780d297ae4662053d17e58fd52
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64409
Analysis date: Sat, 25 Jul 2026 07:15:25 -0400
ActionableScore: 3
ActionableScore lower bound: 0
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A logic error in btmtksdio_txrx_work() can cause an infinite loop after the intended timeout expires, keeping the SDIO host held and causing a persistent Bluetooth driver denial of service on affected MediaTek SDIO hardware.

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

The original Linux kernel CVE announcement for CVE-2026-64409 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64409

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: YES

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

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

CVE-2026-64409	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'btmtksdio_txrx_work() can enter an infinite loop because the timeout check uses an OR condition with time_is_before_jiffies(txrx_timeout). After the 5*HZ timeout expires, the old condition can remain true forever, so the worker may never terminate and may keep the SDIO host held. This can block btmtksdio_flush() and HCI device open paths, causing denial of service for the Bluetooth device and related driver operations. For the CVSS the PR:N paranoid interpretation is used only for an adjacent Bluetooth attacker scenario where nearby radio activity can keep the vulnerable interrupt processing path active on affected MediaTek SDIO hardware. The more typical local administrative trigger is PR:H. The issue is not Internet reachable and there is no evidence of memory corruption, information disclosure, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2)  SKIP CVE-2026-64409 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WARNONLY IMPROVEONLY  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

Paranoid scoring:

* Firmware-mediated external influence: +1. The affected path depends on Bluetooth SDIO interrupt/status behavior and may be influenced by controller or radio activity on affected MediaTek SDIO Bluetooth hardware.
* Reliable kernel crash / strong DoS: +1. The worker can enter an infinite loop and keep the SDIO host held, causing hung btmtksdio_flush() and blocking HCI open/flush paths.
* Availability impact realistic: +1. The impact is persistent device/driver-level denial of service rather than a transient warning.
* Broad/default/common subsystem: +1. Bluetooth is commonly deployed, although this specific driver is hardware-dependent.
* Hard or unreliable trigger / special conditions: -1. Practical attacker control over the interrupt loop is uncertain and likely depends on specific hardware state, firmware behavior, and traffic conditions.

Conservative scoring:

* Reliable DoS: +1.
* Availability impact realistic: +1.
* Requires admin/root/device-management privileges in typical local trigger: -2.
* Hardware-specific driver path: -1.
* Conservative score floored to 0.

No memory corruption, UAF, OOB write, privilege escalation, confidentiality impact, or integrity impact is supported by the patch.

## 3. Reachability analysis

The typical local trigger appears to involve privileged Bluetooth device management paths such as opening, flushing, resetting, or otherwise controlling the HCI device. In normal deployments this is usually restricted to root or a privileged system service, so the conservative interpretation is not unprivileged.

A paranoid interpretation is that adjacent Bluetooth activity or firmware-mediated interrupt behavior might keep int_status active long enough to hit the broken timeout logic. This is not Internet reachable and requires affected MediaTek SDIO Bluetooth hardware. Namespaces do not obviously lower the privilege requirement unless a container or sandbox is delegated Bluetooth device control.

## 4. Severity interpretation

This behaves like a DoS-only logic bug, not an Important-class memory corruption issue. The patch fixes an incorrect loop condition from `int_status || time_is_before_jiffies(txrx_timeout)` to `int_status && time_is_after_jiffies(txrx_timeout)`, so the evidence points to infinite loop and resource lockup rather than corrupt memory or privilege escalation.

Theoretical external influence exists only through adjacent Bluetooth or firmware/device behavior. Realistic exploitation evidence is limited, so this is best treated as ordinary Moderate to borderline actionable Moderate, with manual review focused on whether an unprivileged adjacent attacker can reliably trigger the condition.

## 5. One-sentence report phrase

A logic error in btmtksdio_txrx_work() can cause an infinite loop after the intended timeout expires, keeping the SDIO host held and causing a persistent Bluetooth driver denial of service on affected MediaTek SDIO hardware.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the practical score depends on whether adjacent Bluetooth activity can reliably trigger the interrupt loop without local privileged device control.

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

Patch: Bluetooth: btmtksdio: fix infinite loop in btmtksdio_txrx_work()
Commit: f6682c23b6fac4780d297ae4662053d17e58fd52
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6682c23b6fac4780d297ae4662053d17e58fd52

Commit description:

Every once in a while we see a hung btmtksdio_flush() task:

 INFO: task kworker/u17:0:189 blocked for more than 122 seconds.
 __cancel_work_timer+0x3f4/0x460
 cancel_work_sync+0x1c/0x2c
 btmtksdio_flush+0x2c/0x40
 hci_dev_open_sync+0x10c4/0x2190
 [..]

It all boils down to incorrect time_is_before_jiffies() usage in
btmtksdio_txrx_work().  The btmtksdio_txrx_work() loop is expected
to be terminated if running for longer than 5*HZ.  However the
timeout check is twisted:  time_is_before_jiffies(old_jiffies + 5*HZ)
evaluates to true when old_jiffies + 5*HZ is in the past i.e. when a
timeout has occurred.  Using OR with time_is_before_jiffies(txrx_timeout)
means that:
- before the 5-second timeout: the condition is `int_status || false`,
  so it loops as long as there are pending interrupts.
- after the 5-second timeout: the condition becomes `int_status || true`,
  which is always true.

When the loop becomes infinite btmtksdio_txrx_work() loop never
terminates and never releases the SDIO host.

Fix loop termination condition to actually enforce a 5*HZ timeout.

Fixes: 26270bc ("Bluetooth: btmtksdio: move interrupt service to work")
Cc: stable@vger.kernel.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/bluetooth/btmtksdio.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=f6682c23b6fac4780d297ae4662053d17e58fd52

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

The original Linux kernel CVE announcement for CVE-2026-64409 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64409

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 0
  Paranoid ActionableScore: 3

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).