[PATCH 1/2] tracing: Check return value of __register_event() in trace_module_add_events()

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

trace_module_add_events() ignores the return value of __register_event()
and unconditionally calls __add_event_to_tracers() for each event.

If __register_event() fails (for example, if event_init() fails), the
trace_event_call is not added to ftrace_events list, but
__add_event_to_tracers() still creates a trace_event_file pointing to it.
If module loading subsequently fails and module memory is freed, tracing
state retains a stale trace_event_call pointer in trace_event_file,
leading to a use-after-free when tracefs or tracing subsystem operations
are later executed.

Fix this by checking the return value of __register_event() and only
calling __add_event_to_tracers() if event registration succeeded.

Fixes: ae63b31e4d0e ("tracing: Separate out trace events from global variables")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 kernel/trace/trace_events.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 956692856fa8..c01b10b99f67 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -3933,8 +3933,8 @@ static void trace_module_add_events(struct module *mod)
 	end = mod->trace_events + mod->num_trace_events;
 
 	for_each_event(call, start, end) {
-		__register_event(*call, mod);
-		__add_event_to_tracers(*call);
+		if (!__register_event(*call, mod))
+			__add_event_to_tracers(*call);
 	}
 
 	update_cache_events(mod);