# CVE-2024-46840: btrfs: clean up our handling of refs == 0 in snapshot delete

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-09-27 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 2.6.31

## Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: clean up our handling of refs == 0 in snapshot delete In reada we BUG_ON(refs == 0), which could be unkind since we aren't holding a lock on the extent leaf and thus could get a transient incorrect answer. In walk_down_proc we also BUG_ON(refs == 0), which could happen if we have extent tree corruption. Change that to return -EUCLEAN. In do_walk_down() we catch this case and handle it correctly, however we return -EIO, which -EUCLEAN is a more appropriate error code. Finally in walk_up_proc we have the same BUG_ON(refs == 0), so convert that to proper error handling. Also adjust the error message so we can actually do something with the information.

## 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.
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## 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/c847b28a799733b04574060ab9d00f215970627d
- https://git.kernel.org/stable/c/71291aa7246645ef622621934d2067400380645e
- https://git.kernel.org/stable/c/c60676b81fab456b672796830f6d8057058f029c
- https://git.kernel.org/stable/c/728d4d045b628e006b48a448f3326a7194c88d32
- https://git.kernel.org/stable/c/9cc887ac24b7a0598f4042ae9af6b9a33072f75b
- https://git.kernel.org/stable/c/7d1df13bf078ffebfedd361d714ff6cee1ff01b9
- https://git.kernel.org/stable/c/03804641ec2d0da4fa088ad21c88e703d151ce16
- https://git.kernel.org/stable/c/b8ccef048354074a548f108e51d0557d6adfd3a3

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