Preface: KMSAN (Kernel Memory Sanitizer) was developed by Google. It is a dynamic error detector for the Linux kernel that finds uninitialized memory accesses.
Background: The main feature of fuse_dentry_revalidate() in Linux is to verify and refresh the validity of a directory entry (dentry) and its associated inode in the kernel’s cache before they are used. It bridges the gap between the kernel’s Virtual File System (VFS) and the userspace FUSE daemon.
The frequency of fuse_dentry_revalidate() calls in an HPC process is highly frequent and scales directly with metadata-intensive file operations. In a typical High-Performance Computing (HPC) workload, this function can be triggered millions of times per second, often becoming a major performance bottleneck due to excessive network round-trips to the storage server.
The Linux Kernel VFS (Virtual File System) calls fuse_dentry_revalidate() every time a process attempts to look up, open, or stat a file path to verify if the cached directory entry (dentry) is still valid.
HPC applications frequently invoke this function due to specific behavioral patterns:
- Massive File Scanning: MPI jobs searching through deep directory structures or loading millions of small shared data files.
- Shared Library Loading: Thousands of parallel processes concurrently running ld.so, which searches LD_LIBRARY_PATH and issues repetitive stat() and open() calls on shared files (e.g., Python workloads loading packages like NumPy).
- N-to-N File Access: Multiple compute nodes constantly polling or reading files created by other nodes, forcing the kernel to re-validate the cache.
Vulnerability details: CVE-2026-53311 is a memory handling vulnerability in the FUSE (Filesystem in Userspace) subsystem of the Linux Kernel. The primary impact is system availability loss and potential internal kernel memory disclosure.
Attack Vector: Exploitation requires local access. An attacker must be able to mount a FUSE filesystem or trigger fuse_dentry_revalidate through file operations like opening a path.
How to Mitigate:Update Kernel: The issue is resolved by upgrading your Linux kernel to 6.18.34, 7.0.10, or applying the upstream patch across applicable stable releases.
Official announcement: Please refer to the link for details – https://www.tenable.com/cve/CVE-2026-53311