tracing: Fix some alloc_event_probe() error handling bugs

There are two bugs in this code.  First, if the kzalloc() fails it leads
to a NULL dereference of "ep" on the next line.  Second, if the
alloc_event_probe() function returns an error then it leads to an
error pointer dereference in the caller.

Link: https://lkml.kernel.org/r/20210824115150.GI31143@kili

Fixes: 7491e2c4 ("tracing: Add a probe that attaches to trace events")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_eprobe.c

@@ -151,7 +151,7 @@ static struct trace_eprobe *alloc_event_probe(const char *group,
 
 	ep = kzalloc(struct_size(ep, tp.args, nargs), GFP_KERNEL);
 	if (!ep) {
-		trace_event_put_ref(ep->event);
+		trace_event_put_ref(event);
 		goto error;
 	}
 	ep->event = event;
@@ -851,7 +851,8 @@ static int __trace_eprobe_create(int argc, const char *argv[])
 		ret = PTR_ERR(ep);
 		/* This must return -ENOMEM, else there is a bug */
 		WARN_ON_ONCE(ret != -ENOMEM);
-		goto error;	/* We know ep is not allocated */
+		ep = NULL;
+		goto error;
 	}
 
 	argc -= 2; argv += 2;