Linux Kernel FUSE Filesystem Hang Vulnerability During Synchronous Initialization

A vulnerability in the Linux kernel's FUSE (Filesystem in Userspace) implementation can cause the filesystem creation process to hang. This issue arises when the server unexpectedly exits while processing the FUSE_INIT command during synchronous initialization. In such cases, all threads except the mounting thread will terminate, leaving the device file descriptor open and preventing an abort. This behavior is a regression from the asynchronous mounting process, where the FUSE_INIT handling does not create a recursive system call that keeps the file descriptor open.

Impact

This vulnerability can lead to a deadlock situation where the filesystem creation process hangs indefinitely, causing potential disruptions in operations that rely on that filesystem.

Reproduction

To reproduce this vulnerability, initiate a synchronous FUSE mount and then force the server to crash or exit while it is processing the FUSE_INIT command. This will cause the mounting process to hang, as it will keep the device file descriptor open and prevent an abort from occurring.

Remediation

Users can upgrade to the latest version of the Linux kernel where this vulnerability has been addressed.