In the Linux kernel, the following vulnerability has been resolved: perf/ftrace: Fix WARNING in __unregister_ftrace_function perf_ftrace_f

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

perf/ftrace: Fix WARNING in __unregister_ftrace_function

perf_ftrace_function_unregister() unconditionally calls
unregister_ftrace_function() without checking whether the ftrace_ops
was ever successfully registered. This triggers a WARN_ON in
__unregister_ftrace_function() when the ops doesn't have
FTRACE_OPS_FL_ENABLED set.

This can happen during perf_event_alloc() error cleanup when
perf_trace_destroy() is called via __free_event() on an event whose
ftrace_ops registration failed or was already torn down by
perf_try_init_event()'s err_destroy path.

The call path is:
perf_event_alloc() error cleanup
-> __free_event()
-> event->destroy() [tp_perf_event_destroy]
-> perf_trace_destroy()
-> perf_trace_event_close()
-> TRACE_REG_PERF_CLOSE
-> perf_ftrace_function_unregister()
-> unregister_ftrace_function()
-> __unregister_ftrace_function()
-> WARN_ON(!(ops->flags & FTRACE_OPS_FL_ENABLED))

Fix this by checking FTRACE_OPS_FL_ENABLED before attempting to
unregister. If the ops is not enabled, just free the filter and
return success.