CVE-2026-90066

In the Linux kernel, the following vulnerability has been resolved:

samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify

ftrace_direct_multi_init() assigns kthread_run()'s return value to
simple_tsk without an IS_ERR() check. When kthread_run() fails it
returns ERR_PTR(-ENOMEM), but init still returns 0, so the module loads
with simple_tsk holding an error pointer. On unload,
ftrace_direct_multi_exit() then passes that ERR_PTR to kthread_stop(),
leading to a null-pointer-dereference.

Check the return value of kthread_run() with IS_ERR(); on failure,
unregister the ftrace direct call and propagate the error code.