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CVE Record

CVE-2025-39999: blk-mq: fix blk_mq_tags double free while nr_requests grown

In the Linux kernel, the following vulnerability has been resolved: blk-mq: fix blk_mq_tags double free while nr_requests grown In the case user trigger tags grow by queue sysfs attribute nr_requests, hctx->sched_tags will be freed directly and replaced with a new allocated tags, see blk_mq_tag_update_depth(). The problem is that hctx->sched_tags is from elevator->et->tags, while et->tags is still the freed tags, hence later elevator exit will try to free the tags again, causing kernel panic. Fix this problem by replacing et->tags with new allocated tags as well. Noted there are still some long term problems that will require some refactor to be fixed thoroughly[1]. [1] https://lore.kernel.org/all/20250815080216.410665-1-yukuai1@huaweicloud.com/

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This Linux kernel issue can make an affected system crash when block-device queue request depth is increased through the nr_requests sysfs setting. The business impact is availability, not data theft, based on the provided sources. Severity and CVSS are not available, and there is no KEV evidence of active exploitation.

Executive priority

Treat this as a reliability patch for Linux infrastructure, especially systems where storage tuning is automated. It does not currently justify emergency response language from the provided evidence, but kernel panic risk can affect service availability.

Technical view

In blk-mq, growing nr_requests can replace hctx->sched_tags after freeing the old tag structure, while elevator->et->tags still points to the freed memory. Later elevator exit may free it again, causing a double free and kernel panic. The fix updates et->tags to the newly allocated tags.

Likely exposure

Likely exposure is Linux systems running affected kernel builds where administrators, automation, or storage tuning tools can change block queue nr_requests. The source bundle lists Linux 6.17, 6.17.1, 6.18, and 6.16.11 as affected, but distro backport status must be checked separately.

Exploitation context

The provided sources describe a user-triggered path through the queue sysfs nr_requests attribute, ending in a later kernel panic during elevator exit. They do not show remote exploitation, public exploit code, privilege requirements, or active exploitation.

Researcher notes

Evidence is limited to the kernel CVE description and stable commit references. The affected-version data appears sparse and should be reconciled with upstream stable branches and distro advisories. The source also notes longer-term blk-mq tag lifetime issues requiring future refactor work.

Mitigation direction

  • Apply vendor kernel updates containing the referenced stable fixes.
  • Check distribution advisories for backported fixes before relying on version numbers.
  • Restrict block queue sysfs tuning to trusted administrative workflows.
  • Avoid changing nr_requests on affected systems until patched, where operationally feasible.
  • Prioritize high-availability storage hosts and shared compute nodes.

Validation and detection

  • Inventory running Linux kernel versions and distro patch levels.
  • Confirm whether the referenced stable commits are present in deployed kernels.
  • Review automation that writes block queue nr_requests settings.
  • Check recent kernel logs for block-layer panics after queue tuning changes.
  • Test patched kernels in staging before production rollout.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
4Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux58567d8e95c096ad234963df90a2ca518901f4b6, f5a6604f7a4405450e4a1f54e5430f47290c500f, f5a6604f7a4405450e4a1f54e5430f47290c500f, 6.16.4unaffected
LinuxLinux6.17, 0, 6.16.11, 6.17.1, 6.18affected
Weakness

CWE details

No CWE listed

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