Linux Kernel ftrace Recursive Locking Vulnerability in Direct Mutex

A vulnerability in the Linux kernel's ftrace functionality allows for recursive locking of the direct_mutex, which can lead to a deadlock situation. This issue occurs in versions of the Linux kernel through 6.0.0-rc6. The problem arises when the ftrace_modify_direct_caller function tries to acquire a lock that is already held by the same task, creating a potential deadlock. This vulnerability was reported by Naveen N. Rao.

Impact

Exploitation of this vulnerability causes a deadlock by creating a situation where a task holds a lock and then attempts to acquire it again, leading to a halt in processing.

Reproduction

The vulnerability can be reproduced by loading a specific ftrace sample module that modifies direct callers. This module will trigger a warning about possible recursive locking, indicating that the direct_mutex is being locked recursively by the same task, which can be observed in the kernel's log.

Remediation

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