tracing: tprobe-events: Fix a memory leak when tprobe with $retval

Fix a memory leak when a tprobe is defined with $retval. This
combination is not allowed, but the parse_symbol_and_return() does
not free the *symbol which should not be used if it returns the error.
Thus, it leaks the *symbol memory in that error path.

Link: https://lore.kernel.org/all/174055072650.4079315.3063014346697447838.stgit@mhiramat.tok.corp.google.com/

Fixes: ce51e6153f ("tracing: fprobe-event: Fix to check tracepoint event and return")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: stable@vger.kernel.org

kernel/trace/trace_fprobe.c

@@ -1056,6 +1056,8 @@ static int parse_symbol_and_return(int argc, const char *argv[],
 			if (is_tracepoint) {
 				trace_probe_log_set_index(i);
 				trace_probe_log_err(tmp - argv[i], RETVAL_ON_PROBE);
+				kfree(*symbol);
+				*symbol = NULL;
 				return -EINVAL;
 			}
 			*is_return = true;