CVE-2025-68173

Vulnerability

A soft lockup (RCU stall) can occur in the Linux kernel's ftrace subsystem ftrace when loading a module that contains a large number of traceable functions. The root cause is that the function ftrace_module_enable iterates over all traceable functions in the module and, for each one, calls kallsyms_lookup while holding an RCU read lock and with preemption disabled. This can consume excessive CPU time, triggering a kernel panic on systems with voluntary preemption models.

Exploitation

No special privileges or network access are required to trigger this condition; it is a denial-of-service scenario that arises naturally during normal system administration when a large module (e.g., the amdgpu graphics driver) is loaded. The bug is a logic error in the kernel's tracing infrastructure, not a memory corruption or privilege escalation.

ImpactAn attacker who can cause a large module to be loaded (e.g., by inserting a USB device that triggers module autoloading) can induce a soft lockup, leading to a system hang or crash. This is a denial-of-service vulnerability affects the availability of the system.

MitigationThe fix adds a

cond_resched() call inside the loop in ftrace_module_enable, allowing the scheduler to preempt the task and avoid the RCU stall. This mirrors the same approach used in previous fixes for similar issues in ftrace (commits d0b24b4e91fc and 42ea22e754ba). The patch has been applied to the stable kernel tree [1][2].