[CVE-2026-64496][MODERATE REGULAR] iio: event: Fix event FIFO reset race

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

CVE: CVE-2026-64496
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: iio: event: Fix event FIFO reset race
Commit: 9dc84ba4be5bbeb29ee49efe6cea2cb32c461424
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9dc84ba4be5bbeb29ee49efe6cea2cb32c461424
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64496
Analysis date: Sat, 25 Jul 2026 09:55:43 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline Moderate / manual review recommended
Manual review required: YES

Summary:
A local race in the IIO event fd creation path can allow `kfifo_to_user()` to run concurrently with `kfifo_reset_out()`, corrupting FIFO indexes and causing an out-of-bounds read that may leak adjacent kernel memory to userspace.

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

The original Linux kernel CVE announcement for CVE-2026-64496 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64496

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64496	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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:N/A:L';CWE-362;CWE-125;*CWE-200;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N';BEST CVSS score: '5.3';DESCR 'A race in the IIO event fd creation path can let one thread read from the newly installed event fd while another thread is still resetting the event FIFO. The kfifo_to_user path can then run in parallel with kfifo_reset_out, leaving the FIFO out index inconsistent with the in index and allowing a later read to copy beyond the event FIFO buffer. This is an out of bounds read and can leak adjacent kernel memory to userspace. For the CVSS the PR:L is used because a local process needs access to the IIO event ioctl and can use a second thread in the same process to race reads against fd creation. The issue is not network reachable. Impact is primarily confidentiality loss through kernel memory disclosure, with no direct evidence of arbitrary write or privilege escalation in this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate / manual review recommended (with actual score 3)	YES	OOB LOCK RACE LEAK LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline Moderate / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process with access to the relevant IIO device and `IIO_GET_EVENT_FD_IOCTL` can attempt the race using another thread in the same fd table.
* Weak read-only OOB primitive / kfifo state corruption candidate: +1. The race can corrupt FIFO `in` / `out` bookkeeping and cause an out-of-bounds read, but the patch does not show an OOB write or object replacement primitive.
* Confidentiality impact plausible: +1. The commit explicitly states that a later `read()` can copy more data than the event FIFO contains and leak adjacent kernel memory to userspace.
* Hard or unreliable race: -1. Triggering requires a narrow timing window after `anon_inode_getfd()` installs the fd but before the ioctl returns the fd number to userspace.

Paranoid difference:

* Race penalty not applied in the paranoid score. The fd number may be guessable by another thread sharing the fd table, and the commit describes a concrete reachable interleaving, so treating the race as practically testable is defensible.

Not applied:

* No remote/network trigger.
* No strong generic memory corruption signal, because this is an OOB read / information disclosure path, not an OOB write, UAF reclaim, double free, arbitrary write, or type confusion.
* No privilege escalation bonus, because the patch context does not show a write primitive, callback control, object replacement, or other LPE-enabling primitive.
* No Dirty-Pipe-like or page-cache ownership bypass signal.

## 3. Reachability analysis

The bug is locally reachable through the IIO event fd creation path. The attacker needs a local process that can access the relevant IIO device node and issue the event fd ioctl. In many deployments this may require membership in a device-specific group, udev-granted access, or a privileged service context, but it is not inherently full root-only from the kernel interface itself.

Namespaces and containers do not automatically make this broadly reachable unless the IIO device node is exposed into the container. The path is not network reachable. The affected subsystem is hardware/configuration dependent, because it requires IIO devices with event support, but the vulnerable operation itself is an ordinary local device interface once exposed.

Call-site confidence: high. The commit message directly identifies both sides of the race, `iio_event_getfd()` and `iio_event_chrdev_read()`, and describes the concrete `kfifo_reset_out()` versus `kfifo_to_user()` interaction.

## 4. Severity interpretation

This behaves more like an ordinary-to-borderline Moderate issue with manual-review relevance, not an Important-class vulnerability. The strongest demonstrated impact is local kernel memory disclosure through an out-of-bounds read caused by corrupted FIFO indices. Theoretical escalation is not impossible for kernel information leaks in general, but this patch does not provide evidence of an arbitrary write, UAF reclaim, type confusion, or controlled object corruption.

The issue should not be treated as a pure cleanup or auto-closed low-risk bug because the disclosed primitive is user-visible kernel memory leakage. It also should not be promoted to Important solely from the race condition, because the primitive is read-only and requires a local device-access scenario plus timing.

## 5. One-sentence report phrase

A local race in the IIO event fd creation path can allow `kfifo_to_user()` to run concurrently with `kfifo_reset_out()`, corrupting FIFO indexes and causing an out-of-bounds read that may leak adjacent kernel memory to userspace.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug includes a concrete local out-of-bounds kernel memory read and potential information disclosure. Even though no write primitive or privilege-escalation path is shown, kernel memory disclosure bugs should be reviewed manually rather than auto-closed.

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

Patch: iio: event: Fix event FIFO reset race
Commit: 9dc84ba4be5bbeb29ee49efe6cea2cb32c461424
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9dc84ba4be5bbeb29ee49efe6cea2cb32c461424

Commit description:

`iio_event_getfd()` creates the event file descriptor with
`anon_inode_getfd()`, which allocates a new fd, creates the anonymous
file and installs it in the process fd table before returning to the
caller.

The IIO code resets the event FIFO after `anon_inode_getfd()` has returned,
but before `IIO_GET_EVENT_FD_IOCTL` has copied the fd number to userspace.
But since fd tables are shared between threads, another thread can guess
the newly allocated fd number and issue a `read()` on it as soon as the fd
has been installed.

This means the `kfifo_to_user()` in `iio_event_chrdev_read()` can run in
parallel with the `kfifo_reset_out()` in `iio_event_getfd()`.

The kfifo documentation says that `kfifo_reset_out()` is only safe when it
is called from the reader thread and there is only one concurrent reader.
Otherwise it is dangerous and must be handled in the same way as
`kfifo_reset()`.

If that happens, `kfifo_to_user()` can advance the FIFO `out` index based
on state from before the reset, after the reset has already moved the `out`
index to the current `in` index. That can leave the FIFO with an `out`
index past the `in` index. A later `read()` can then see an underflowed
FIFO length and copy more data than the event FIFO buffer contains. This
can result in an out-of-bounds read and leak adjacent kernel memory to
userspace.

Move the FIFO reset before `anon_inode_getfd()`. At that point the event fd is
marked busy, but the new fd has not been installed yet, so userspace cannot
access it while the FIFO is reset.

Fixes: b91acca ("iio:event: Fix and cleanup locking")
Reported-by: Codex:gpt-5.5
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iio/industrialio-event.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=9dc84ba4be5bbeb29ee49efe6cea2cb32c461424

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

The original Linux kernel CVE announcement for CVE-2026-64496 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64496

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:H/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:L
  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: 2
  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).