[CVE-2026-46089][LOW] zram: do not forget to endio for partial discard requests

[CVE-2026-46089][LOW] zram: do not forget to endio for partial discard requests

[AL-KERNEL]

CVE: CVE-2026-46089
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: zram: do not forget to endio for partial discard requests
Commit: 2d1f18efccdb8b29552399d024c36b705447e975
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2d1f18efccdb8b29552399d024c36b705447e975
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46089
Analysis date: Wed, 27 May 2026 11:10:37 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A partial discard to zram can return without `bio_endio()`, leaving the submitter stuck in `submit_bio_wait()` and causing local DoS only when discard access to the zram device is available.

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

The original Linux kernel CVE announcement for CVE-2026-46089 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46089

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-2026-46089	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-459;CWE-755;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A local denial of service can occur in zram partial discard handling because zram_bio_discard() could return without calling bio_endio(). A partial discard request such as a 4k discard on a 64k page system can leave the submitter waiting forever in submit_bio_wait(). For the CVSS the PR:L is used only in the paranoid score when an untrusted local user or delegated service can issue discard operations against a zram block device. The typical case requires privileged block device access, so PR:H is more realistic. The issue is not network reachable and does not involve UAF, out of bounds access, arbitrary write, information disclosure, or privilege escalation. Impact is denial of service only through hung discard callers or blocked storage management operations.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	SIMPLEFIX MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Availability impact plausible: +1
  A partial discard can leave the submitter blocked forever in `submit_bio_wait()`.

* Requires privileged block-device access in typical deployments: -2
  Issuing discard against `/dev/zram0` normally requires root or delegated block-device permissions.

* Configuration/path dependent: -1
  The demonstrated case depends on partial discard geometry such as 4k discard on a 64k page system.

Paranoid signals:

* Local delegated trigger concern: +1
  Some environments may allow a service account, container, or untrusted local workload to issue discard to a zram device.

* Availability impact realistic when reachable: +1
  If reachable, the request can hang the caller indefinitely and block storage management operations.

No signals apply for remote reachability, memory corruption, UAF, OOB access, arbitrary write, information disclosure, privilege escalation, or security-boundary bypass.

## 3. Reachability analysis

The issue is local. A process must issue a partial discard request to a zram block device. In normal deployments, direct discard access to `/dev/zram*` is privileged, but delegated block-device access or containerized environments can reduce the effective privilege requirement.

The issue is not network reachable. It is most relevant on systems where page size and discard granularity allow partial discards, such as the 64k page / 4k discard example.

## 4. Severity interpretation

This behaves like a Low-like local DoS. The patch fixes a missing `bio_endio()` on an early return path, not memory corruption.

Realistic impact is a hung caller or blocked storage operation. There is no evidence of C/I impact or privilege escalation.

## 5. One-sentence report phrase

A partial discard to zram can return without `bio_endio()`, leaving the submitter stuck in `submit_bio_wait()` and causing local DoS only when discard access to the zram device is available.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a local IO-completion DoS with privileged or delegated block-device access requirements and no supported memory corruption or privilege-escalation primitive.

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

Patch: zram: do not forget to endio for partial discard requests
Commit: 2d1f18efccdb8b29552399d024c36b705447e975
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2d1f18efccdb8b29552399d024c36b705447e975

Commit description:

As reported by Qu Wenruo and Avinesh Kumar, the following

 getconf PAGESIZE
 65536
 blkdiscard -p 4k /dev/zram0

takes literally forever to complete.  zram doesn't support partial
discards and just returns immediately w/o doing any discard work in such
cases.  The problem is that we forget to endio on our way out, so
blkdiscard sleeps forever in submit_bio_wait().  Fix this by jumping to
end_bio label, which does bio_endio().

Link: https://lore.kernel.org/20260331074255.777019-1-senozhatsky@chromium.org
Fixes: 0120dd6 ("zram: make zram_bio_discard more self-contained")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reported-by: Qu Wenruo <wqu@suse.com>
Closes: https://lore.kernel.org/linux-block/92361cd3-fb8b-482e-bc89-15ff1acb9a59@suse.com
Tested-by: Qu Wenruo <wqu@suse.com>
Reported-by: Avinesh Kumar <avinesh.kumar@suse.com>
Closes: https://bugzilla.suse.com/show_bug.cgi?id=1256530
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/block/zram/zram_drv.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=2d1f18efccdb8b29552399d024c36b705447e975

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

The original Linux kernel CVE announcement for CVE-2026-46089 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46089

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:H/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: 0
  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).