[CVE-2026-46275][MODERATE 7.0] Bluetooth: hci_uart: fix UAFs and race conditions in close and init paths

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

CVE: CVE-2026-46275
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: hci_uart: fix UAFs and race conditions in close and init paths
Commit: 78aad93e938f013d9272fe0ee168f27883afa95c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=78aad93e938f013d9272fe0ee168f27883afa95c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46275
Analysis date: Mon, 08 Jun 2026 10:59:45 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
Bluetooth hci_uart close and init path races can leave workqueue callbacks running after UART or HCI device teardown, causing UAF and double-free conditions that are locally triggerable and may lead to kernel crash, with limited but non-negligible memory-corruption risk.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46275 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46275

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-46275	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-415;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'Bluetooth hci_uart has lifecycle races in the close and init paths where init_ready or write_work can remain scheduled after the hu object or the hdev object is torn down. A local attacker who can interact with the relevant Bluetooth UART TTY path may trigger a hangup or close during initialization, allowing later workqueue execution to dereference freed state. The same teardown area also includes a possible double free of hu tx_skb and a vendor close callback UAF when hci_free_dev runs before proto close. For the CVSS the PR:L is used for the paranoid score because reliable triggering needs local code execution or access to the affected TTY or Bluetooth UART control path, but it does not necessarily require full host administrator privileges in all deployments. The issue is not directly network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel memory corruption, so manual review is warranted.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	NULLPTR INIT RACE ERRORPATH UAF SKB TIMER HARDWARE TEST  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged or reduced-privilege trigger: +1
  The bug is local and depends on interaction with the affected Bluetooth HCI UART TTY lifecycle. Full host root is not necessarily required in all deployments if a local process can access the relevant TTY or Bluetooth UART control path.

* Memory corruption, strong corruption primitive: +2
  The commit explicitly describes UAFs and a double-free of `hu->tx_skb`. This is stronger than a pure NULL dereference or validation-only bug.

* Real lifetime corruption: +1
  Work items can outlive the `hu` or `hdev` objects, and callbacks can dereference objects after teardown.

* Reliable kernel crash / strong DoS: +1
  Deferred work dereferencing freed state or double-freeing SKBs can realistically crash the kernel.

* Hard or unreliable race / special timing required: -1
  Reliable triggering depends on close/init/hangup timing and concurrent workqueue or timer behavior.

Paranoid-only additions:

* Confidentiality impact plausible: +1
  Kernel UAF and double-free bugs can sometimes be shaped beyond DoS, although no concrete leak primitive is shown.

* Integrity impact plausible: +1
  The double-free and UAF class makes limited integrity impact technically defensible for triage, but not proven.

No extra LPE bonus was added because the patch does not show attacker-controlled reclaim, type confusion, callback pointer corruption, arbitrary write, or a demonstrated privilege-escalation primitive.

## 3. Reachability analysis

The issue is not network reachable. It is reachable through local Bluetooth HCI UART lifecycle operations involving TTY close, hangup, initialization failure, or HCI device teardown. Typical production systems may restrict this path to privileged Bluetooth management services or users with access to the UART device, but reduced-privilege service accounts, containerized root, or delegated device access can make PR:L a reasonable paranoid interpretation. The affected subsystem is not universally exposed by default, but Bluetooth UART is common on embedded, laptop, and platform Bluetooth devices.

## 4. Severity interpretation

This is more than an ordinary Moderate DoS because the patch fixes explicit UAF and double-free conditions, not just a warning or NULL dereference. Realistic exploitation evidence primarily supports local kernel crash or instability. Theoretical impact can extend to confidentiality or integrity because kernel lifetime corruption is present, but no strong LPE primitive is demonstrated. Therefore the conservative result is borderline manual-review territory, while the paranoid result is Actionable Moderate and should not be auto-closed.

## 5. One-sentence report phrase

Bluetooth hci_uart close and init path races can leave workqueue callbacks running after UART or HCI device teardown, causing UAF and double-free conditions that are locally triggerable and may lead to kernel crash, with limited but non-negligible memory-corruption risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the patch explicitly fixes UAF and double-free conditions in asynchronous workqueue and teardown paths, and these bug classes are often underestimated during initial automated triage.

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

Patch: Bluetooth: hci_uart: fix UAFs and race conditions in close and init paths
Commit: 78aad93e938f013d9272fe0ee168f27883afa95c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=78aad93e938f013d9272fe0ee168f27883afa95c

Commit description:

Vulnerabilities leading to Use-After-Free (UAF) and Null Pointer
Dereference (NPD) conditions were observed in the lifecycle management
of hci_uart.

The primary issue arises because the workqueues (init_ready and
write_work) are only flushed/cancelled if the HCI_UART_PROTO_READY
flag is set during TTY close. If a hangup occurs before setup completes,
hci_uart_tty_close() skips the teardown of these workqueues and
proceeds to free the `hu` struct. When the scheduled work executes
later, it blindly dereferences the freed `hu` struct.

Furthermore, several data races and UAFs were identified in the teardown
sequence:
1. Calling hci_uart_flush() from hci_uart_close() without effectively
   disabling write_work causes a race condition where both can concurrently
   double-free hu->tx_skb. This happens because protocol timers can
   concurrently invoke hci_uart_tx_wakeup() and requeue write_work.
2. Calling hci_free_dev(hdev) before hu->proto->close(hu) causes a UAF
   when vendor specific protocol close callbacks dereference hu->hdev.
3. In the initialization error paths, failing to take the proto_lock
   write lock before clearing PROTO_READY leads to races with active
   readers. Additionally, hci_uart_tty_receive() accesses hu->hdev
   outside the read lock, leading to UAFs if the initialization error
   path frees hdev concurrently.

Fix these synchronization and lifecycle issues by:
1. Re-ordering hci_uart_tty_close() to clear HCI_UART_PROTO_READY first,
   followed immediately by a cancel_work_sync(&hu->write_work). Clearing
   the flag locks out concurrent protocol timers from successfully invoking
   hci_uart_tx_wakeup(), effectively rendering the cancellation permanent
   and preventing the tx_skb double-free.
2. Note: Clearing PROTO_READY early causes hci_uart_close() to skip
   hu->proto->flush(). This is perfectly safe in the tty_close path
   because hu->proto->close() executes shortly after, which intrinsically
   purges all protocol SKB queues and tears down the state.
3. Relocating hu->proto->close(hu) strictly prior to hci_free_dev(hdev)
   across all close and error paths to prevent vendor-level UAFs.
4. Moving the hdev->stat.byte_rx increment in hci_uart_tty_receive()
   inside the proto_lock read-side critical section to safely synchronize
   with device unregistration.
5. Adding cancel_work_sync(&hu->write_work) to hci_uart_close() to safely
   flush the workqueue before hci_uart_flush() is invoked via the HCI core.
6. Utilizing cancel_work_sync() instead of disable_work_sync() across
   all paths to prevent permanently breaking user-space retry capabilities.

Fixes: 3b79925 ("Bluetooth: hci_uart: Cancel init work before unregistering")
Cc: stable@vger.kernel.org
Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn>
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/hci_ldisc.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=78aad93e938f013d9272fe0ee168f27883afa95c

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

The original Linux kernel CVE announcement for CVE-2026-46275 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46275

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 4
  Paranoid ActionableScore: 6

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: YES
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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).