tracing: Avoid memory leak in predicate_parse()

In case of errors, predicate_parse() goes to the out_free label
to free memory and to return an error code.

However, predicate_parse() does not free the predicates of the
temporary prog_stack array, thence leaking them.

Link: http://lkml.kernel.org/r/20190528154338.29976-1-tomasbortoli@gmail.com

Cc: stable@vger.kernel.org
Fixes: 80765597bc ("tracing: Rewrite filter logic to be simpler and faster")
Reported-by: syzbot+6b8e0fb820e570c59e19@syzkaller.appspotmail.com
Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
[ Added protection around freeing prog_stack[i].pred ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_filter.c

@@ -428,7 +428,7 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
 	op_stack = kmalloc_array(nr_parens, sizeof(*op_stack), GFP_KERNEL);
 	if (!op_stack)
 		return ERR_PTR(-ENOMEM);
-	prog_stack = kmalloc_array(nr_preds, sizeof(*prog_stack), GFP_KERNEL);
+	prog_stack = kcalloc(nr_preds, sizeof(*prog_stack), GFP_KERNEL);
 	if (!prog_stack) {
 		parse_error(pe, -ENOMEM, 0);
 		goto out_free;
@@ -579,7 +579,11 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
 out_free:
 	kfree(op_stack);
 	kfree(inverts);
-	kfree(prog_stack);
+	if (prog_stack) {
+		for (i = 0; prog_stack[i].pred; i++)
+			kfree(prog_stack[i].pred);
+		kfree(prog_stack);
+	}
 	return ERR_PTR(ret);
 }