[CVE-2026-53185][IMPORTANT] zram: fix use-after-free in zram_bvec_write_partial()

[CVE-2026-53185][IMPORTANT] zram: fix use-after-free in zram_bvec_write_partial()

[AL-KERNEL]

CVE: CVE-2026-53185
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: zram: fix use-after-free in zram_bvec_write_partial()
Commit: 0c2821665ff71be3f4b07ecece384669f2877f6a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c2821665ff71be3f4b07ecece384669f2877f6a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53185
Analysis date: Thu, 25 Jun 2026 06:49:20 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local use-after-free write in `zram_bvec_write_partial()` can occur when an async backing-device read for a `ZRAM_WB` slot completes after the temporary page has been modified and freed, causing kernel memory corruption and possible local DoS or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-53185 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53185

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: IMPORTANT
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
======================================================================

CVE-2026-53185	IMPORTANT	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-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free write can occur in zram_bvec_write_partial() when zram_read_page() is called with a parent bio and selects the asynchronous backing device read path for ZRAM_WB slots. The function can return while the read bio is still in flight, after which the caller updates the temporary page, writes it back, and frees it. The pending asynchronous read may then complete into the freed page, causing kernel memory corruption. For the CVSS the PR:L is used because triggering can be possible from a local user context once zram writeback is configured, for example through swap or block I/O activity, even though initial writeback setup is usually administrative. The issue is not network reachable. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use-after-free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	READ UAF HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  Once zram writeback is configured, local users can plausibly drive swap or block I/O patterns that reach zram partial write paths.

* Privilege escalation plausible: +1 conservative, +2 paranoid
  This is a real write-after-free into a freed page. Conservative scoring treats LPE as plausible but not demonstrated. Paranoid scoring raises this because freed page reuse plus attacker-influenced backing data may become exploitable.

* Generic memory corruption, strong corruption primitive: +2
  The async backing-device read can complete into a page after `__free_page()`, which is a concrete UAF write.

* Real lifetime corruption: +1
  The bug is an async completion lifetime mismatch: the I/O outlives the temporary page buffer.

* Reliable kernel crash / strong DoS: +1
  Writing into freed kernel memory can realistically cause crashes or memory corruption.

* Important filesystem/storage path: +1
  zram is a block/swap storage path, and the affected path involves writeback and page I/O.

* Legacy / non-default execution mode: -1
  Triggering requires zram writeback / `ZRAM_WB` slots, which is not guaranteed in all deployments.

## 3. Reachability analysis

The issue is local, not network reachable. Initial zram writeback setup usually requires administrative configuration, but after zram writeback is enabled, ordinary local memory pressure, swap activity, or block I/O can plausibly reach the vulnerable path. Containers may affect reachability depending on whether they can induce host swap pressure, but the main trigger remains host-local. Realistic exploitation requires `ZRAM_WB` slots and async backing-device reads, so exposure is configuration-dependent but not purely theoretical.

## 4. Severity interpretation

This is not an ordinary Moderate resource leak or NULL dereference. The patch fixes a concrete use-after-free write where an async read may write into a freed page. Realistic demonstrated impact is local kernel memory corruption and DoS. Privilege escalation is not proven by the patch, but it is plausible enough for manual review because the primitive is a real lifetime corruption bug in a storage/page path.

## 5. One-sentence report phrase

A local use-after-free write in `zram_bvec_write_partial()` can occur when an async backing-device read for a `ZRAM_WB` slot completes after the temporary page has been modified and freed, causing kernel memory corruption and possible local DoS or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because it is a real UAF write into freed memory, not merely a warning or constrained validation bug.

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

Patch: zram: fix use-after-free in zram_bvec_write_partial()
Commit: 0c2821665ff71be3f4b07ecece384669f2877f6a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c2821665ff71be3f4b07ecece384669f2877f6a

Commit description:

zram_read_page() picks the sync or async backing device read path based on
whether the parent bio is NULL.  zram_bvec_write_partial() passes its
parent bio down, so for ZRAM_WB slots the read is dispatched
asynchronously and zram_read_page() returns 0 while the bio is still in
flight.  The caller then runs memcpy_from_bvec(), zram_write_page() and
__free_page() on the buffer, leaving the async read to write into a freed
page.

zram_bvec_read_partial() was switched to NULL in commit 4e3c87b
("zram: fix synchronous reads") for the same reason; the write_partial
counterpart was missed.

Link: https://lore.kernel.org/20260528-zram-v3-1-cab86eef8764@gmail.com
Fixes: 8e654f8 ("zram: read page from backing device")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Cunlong Li <shenxiaogll@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Yisheng Xie <xieyisheng1@huawei.com>
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=0c2821665ff71be3f4b07ecece384669f2877f6a

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

The original Linux kernel CVE announcement for CVE-2026-53185 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53185

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).