CVE-2026-89540

Received Received - Intake

Race Condition in Linux Kernel SunRPC GSS Proxy Proc Entry

Publication date: 2026-09-11

Last updated on: 2026-09-14

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: sunrpc: init gssp_lock before publishing proc entry create_use_gss_proxy_proc_entry() publishes /proc/net/rpc/use-gss-proxy via proc_create_data() before init_gssp_clnt() runs mutex_init() on sn->gssp_lock. Once the dentry is linked under proc_subdir_lock it is immediately reachable from userspace, so a write that lands in the window drives set_gssp_clnt() into mutex_lock() on a zero-initialized struct mutex. create_use_gss_proxy_proc_entry(net) proc_create_data("use-gss-proxy", ...) /* dentry live */ init_gssp_clnt(sn) mutex_init(&sn->gssp_lock) /* too late */ write_gssp() set_gssp_clnt(net) mutex_lock(&sn->gssp_lock) /* uninitialized */ gssp_rpc_create(...) sn->gssp_clnt = clnt mutex_unlock(&sn->gssp_lock) The window spans only the two statements between proc_create_data() returning and init_gssp_clnt(), so a writer reaches it only if the registering thread is preempted there while another task is already opening the freshly published file. register_pernet_subsys() runs in preemptible context under pernet_ops_rwsem, so that preemption is possible, and the window widens on auth_rpcgss module load, when the proc entry is created for every live net namespace whose tasks are already running. A writer that wins the race locks a zero-filled struct mutex. On CONFIG_DEBUG_MUTEXES the missing magic value trips a "lock used without init" splat; on a production kernel the fast path acquires the lock via CMPXCHG(owner, 0, current). In the latter case a second writer that arrives before init_gssp_clnt() re-zeroes owner can enter set_gssp_clnt() concurrently, shut down the first writer's clnt while it is still in use, and leak the loser's clnt. Fix by initializing sn->gssp_lock in sunrpc_init_net() so its lifetime matches the sunrpc_net it lives in. sn->gssp_clnt is already NULL from the kzalloc that backs net_generic storage, so the lazy helper is no longer needed; drop init_gssp_clnt(), its prototype, and the call from create_use_gss_proxy_proc_entry(). sunrpc.ko is a build-time dependency of auth_rpcgss.ko, so sunrpc_init_net() has always run on every netns before any auth_gss pernet init can publish the proc entry.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-09-11

Last Modified

2026-09-14

Generated

2026-10-02

AI Q&A

2026-09-12

EPSS Evaluated

2026-09-30

NVD

CVE-2026-89540

EUVD

EUVD-2026-76451

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This is a race condition in the Linux kernel's sunrpc module. The issue occurs when a proc entry is created before a mutex is initialized. Specifically, the gssp_lock mutex is initialized after the /proc/net/rpc/use-gss-proxy entry is published, creating a window where a writer can lock an uninitialized mutex. This may lead to concurrent access issues or memory leaks if the race condition is exploited.

Detection Guidance

This vulnerability is specific to the Linux kernel's sunrpc module and involves a race condition during initialization. Detection requires checking kernel logs for mutex-related errors or crashes during auth_rpcgss module loading. Monitor for messages like 'lock used without init' if CONFIG_DEBUG_MUTEXES is enabled. No direct commands detect this beyond standard kernel monitoring.

Impact Analysis

If exploited, this vulnerability could allow a local attacker to cause a denial of service or memory corruption in the kernel. It may also lead to unexpected behavior in applications relying on the sunrpc module, such as NFS or RPC services. The impact is limited to systems running vulnerable Linux kernel versions with the affected sunrpc module loaded.

Compliance Impact

This vulnerability does not directly affect compliance with standards like GDPR or HIPAA. It is a race condition in the Linux kernel's sunrpc module that could lead to undefined behavior or crashes, but there is no evidence it impacts data protection or privacy requirements specified in these regulations.

Mitigation Strategies

Apply the kernel patch that initializes gssp_lock before proc entry creation. Update to a fixed kernel version where sunrpc_init_net() initializes sn->gssp_lock. If patching is not immediate, avoid loading auth_rpcgss module until the fix is applied to prevent the race condition.

Hi! I’m here to help you understand CVE-2026-89540. Ask me anything about the vulnerability, its impact, or mitigation strategies.

0/70