CVE-2022-50648 in Linux
Resumen
por VulDB • 2026-05-22
Enabling `CONFIG_FTRACE_DIRECT` in the kernel configuration allows for direct function calls via ftrace, which can significantly reduce overhead for specific use cases. However, this feature introduces a potential deadlock scenario when `ftrace_modify_direct_caller` is called from contexts that already hold locks, such as mutexes.
The issue arises because `ftrace_modify_direct_caller` internally calls `register_ftrace_function`, which attempts to acquire the `ftrace_lock`. If the caller of `ftrace_modify_direct_caller` already holds a lock that is also required by another part of the ftrace subsystem (or if the call chain creates a circular dependency), a deadlock occurs. The stack trace provided shows this deadlock happening within `modify_ftrace_direct`, which is called from a kernel thread (`simple_thread`) in the `ftrace_direct_modify` module.
To resolve this, we need to avoid acquiring the `ftrace_lock` again if it's already held or if we are in a context where acquiring it would cause a deadlock. The function `register_ftrace_function_nolock` is designed for this purpose; it performs the registration without attempting to acquire the `ftrace_lock`. This is safe to use in `ftrace_modify_direct_caller` because the caller (`modify_ftrace_direct`) is expected to hold the necessary locks (like `ftrace_lock` or other synchronization primitives) before calling it, or the modification process is designed to be lock-free in specific contexts.
Here is the fix:
```c // In kernel/trace/ftrace.c
// Change this line: // ret = register_ftrace_function(&mc->ops); // To this: ret = register_ftrace_function_nolock(&mc->ops); ```
This change ensures that `ftrace_modify_direct_caller` does not attempt to acquire the `ftrace_lock`, thereby preventing the deadlock observed in the stack trace. The responsibility for ensuring proper synchronization is shifted to the caller, which is appropriate given the design of `ftrace_direct` modifications.
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