Bug 2426105 (CVE-2023-54227)

Summary: CVE-2023-54227 kernel: blk-mq: fix tags leak when shrink nr_hw_queues
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A memory leak flaw was found in the Linux kernel's block multi-queue (blk-mq) subsystem. When the number of hardware queues is reduced via the submit_queues parameter, the tags associated with the removed queues are not freed, causing a memory leak. This occurs because shrinking nr_hw_queues does not deallocate the tags for queues that are no longer needed.
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Description OSIDB Bzimport 2025-12-30 13:09:18 UTC 
In the Linux kernel, the following vulnerability has been resolved:

blk-mq: fix tags leak when shrink nr_hw_queues

Although we don't need to realloc set->tags[] when shrink nr_hw_queues,
we need to free them. Or these tags will be leaked.

How to reproduce:
1. mount -t configfs configfs /mnt
2. modprobe null_blk nr_devices=0 submit_queues=8
3. mkdir /mnt/nullb/nullb0
4. echo 1 > /mnt/nullb/nullb0/power
5. echo 4 > /mnt/nullb/nullb0/submit_queues
6. rmdir /mnt/nullb/nullb0

In step 4, will alloc 9 tags (8 submit queues and 1 poll queue), then
in step 5, new_nr_hw_queues = 5 (4 submit queues and 1 poll queue).
At last in step 6, only these 5 tags are freed, the other 4 tags leaked.
Comment 1 Alexander B 2025-12-31 08:53:14 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025123029-CVE-2023-54227-5c6c@gregkh/T