tracing: Fix allocation of printing set_event file content

The adding of cached events for modules not loaded yet required a
descriptor to separate the iteration of events with the iteration of
cached events for a module. But the allocation used the size of the
pointer and not the size of the contents to allocate its data and caused a
slab-out-of-bounds.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/20250121151236.47fcf433@gandalf.local.home
Reported-by: Sasha Levin <sashal@kernel.org>
Closes: https://lore.kernel.org/all/Z4_OHKESRSiJcr-b@lappy/
Fixes: b355247 ("tracing: Cache ":mod:" events for modules not loaded yet")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: rostedt

kernel/trace/trace_events.c

@@ -1588,7 +1588,7 @@ static void *s_start(struct seq_file *m, loff_t *pos)
 	struct set_event_iter *iter;
 	loff_t l;
 
-	iter = kzalloc(sizeof(iter), GFP_KERNEL);
+	iter = kzalloc(sizeof(*iter), GFP_KERNEL);
 	if (!iter)
 		return NULL;