CVE-2026-53244 in Linux
Summary
by MITRE • 06/25/2026
In the Linux kernel, the following vulnerability has been resolved:
VFS: fix possible failure to unlock in nfsd4_create_file()
atomic_create() in fs/namei.c drops the reference to the dentry when it returns an error. This behaviour was imported into dentry_create() so that it will drop the reference if an error is returned from atomic_create(), though not if vfs_create() returns an error (in the case where ->atomic_create is not supported).
The caller - nfsd4_create_file() - is made aware of this by checking path->dentry, which will either be a counted reference to a dentry, or an error pointer.
However the change to use start_creating()/end_creating() (which landed shortly before the dentry_create() change landed, though was likely developed around the same time) means that nfsd4_create_file() *needs* a valid dentry so that it can unlock the parent.
The net result is that if NFSD exports a filesystem which uses ->atomic_create, and if a call to ->atomic_create returns an error, then nfsd4_create_file() will pass an error pointer to end_creating() and the parent will not be unlocked.
Fix this by changing dentry_create() to make sure path->dentry is always a valid dentry, never an error-pointer. The actual error is already returned a different way.
Note that if ->atomic_create() returns a different dentry (which may not be possible in practice) we are guaranteed (because it is only ever provided by d_spliace_alias()) that it will have the same d_parent and so it will have the same effect when passed to end_creating().
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Analysis
by VulDB Data Team • 06/25/2026
The vulnerability described represents a critical race condition and resource management flaw within the Linux kernel's virtual filesystem layer, specifically affecting the Network File System Daemon (NFSD) implementation. This issue stems from improper handling of dentry references during file creation operations, creating a scenario where parent directory locks may remain permanently acquired. The problem manifests in nfsd4_create_file() function when dealing with filesystems that implement atomic_create operations, particularly those using the NFSv4 protocol. The core technical flaw occurs due to inconsistent reference counting behavior between different kernel subsystems and how error conditions are propagated through the call stack.
The vulnerability arises from a combination of changes made to the kernel's name resolution and file creation mechanisms. When atomic_create() returns an error condition, the fs/namei.c implementation drops its reference to the dentry structure, a behavior that was subsequently imported into dentry_create(). However, this cleanup mechanism fails to account for cases where vfs_create() itself returns an error without utilizing the atomic_create interface. The nfsd4_create_file() function attempts to handle this scenario by checking path->dentry for valid references, but the introduction of start_creating()/end_creating() API calls creates a dependency on having a valid dentry pointer for proper parent unlocking operations.
This security issue directly impacts the availability and correctness of NFS file sharing operations, as it can lead to permanent lock contention on parent directories. When an error occurs during atomic_create execution, the function passes an error pointer to end_creating() instead of a valid dentry structure, preventing proper release of the parent directory lock. The consequence is that subsequent file creation requests targeting the same parent directory will block indefinitely, creating a denial-of-service condition for NFS clients. This flaw operates at the intersection of multiple kernel subsystems and violates fundamental resource management principles.
The fix implemented addresses the root cause by ensuring that dentry_create() always provides a valid dentry reference in path->dentry, regardless of error conditions during the atomic_create process. This approach maintains proper reference counting semantics while ensuring that end_creating() receives appropriate input for releasing parent directory locks. The solution aligns with common security practices for managing kernel resource lifecycles and follows established patterns for error handling in virtual filesystem implementations. The vulnerability demonstrates how seemingly isolated changes to kernel subsystems can create unexpected interactions, highlighting the importance of comprehensive testing across integrated components.
This issue has implications for compliance with security standards such as those outlined in CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and represents a failure to properly manage shared resources in kernel space. The fix ensures that the NFS daemon maintains proper lock discipline even when encountering error conditions during file creation, preventing denial-of-service scenarios that could affect enterprise file server availability. The solution also aligns with ATT&CK framework considerations for privilege escalation and system stability by preventing malicious exploitation of resource management flaws through controlled error conditions.