Bug 2404126 (CVE-2025-39999)

Summary: CVE-2025-39999 kernel: blk-mq: fix blk_mq_tags double free while nr_requests grown
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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OS: Linux   
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Description OSIDB Bzimport 2025-10-15 09:01:56 UTC 
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/
Comment 1 Alexander B 2025-10-16 10:02:50 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025101529-CVE-2025-39999-08ff@gregkh/T