tracing: Make -ENOMEM the default error for parse_synth_field()

parse_synth_field() returns a pointer and requires that errors get
surrounded by ERR_PTR(). The ret variable is initialized to zero, but should
never be used as zero, and if it is, it could cause a false return code and
produce a NULL pointer dereference. It makes no sense to set ret to zero.

Set ret to -ENOMEM (the most common error case), and have any other errors
set it to something else. This removes the need to initialize ret on *every*
error branch.

Fixes: 761a8c58 ("tracing, synthetic events: Replace buggy strcat() with seq_buf operations")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_synth.c

@@ -584,7 +584,7 @@ static struct synth_field *parse_synth_field(int argc, const char **argv,
 {
 	struct synth_field *field;
 	const char *prefix = NULL, *field_type = argv[0], *field_name, *array;
-	int len, ret = 0;
+	int len, ret = -ENOMEM;
 	struct seq_buf s;
 	ssize_t size;
 
@@ -617,10 +617,9 @@ static struct synth_field *parse_synth_field(int argc, const char **argv,
 		len--;
 
 	field->name = kmemdup_nul(field_name, len, GFP_KERNEL);
-	if (!field->name) {
-		ret = -ENOMEM;
+	if (!field->name)
 		goto free;
-	}
+
 	if (!is_good_name(field->name)) {
 		synth_err(SYNTH_ERR_BAD_NAME, errpos(field_name));
 		ret = -EINVAL;
@@ -638,10 +637,9 @@ static struct synth_field *parse_synth_field(int argc, const char **argv,
 		len += strlen(prefix);
 
 	field->type = kzalloc(len, GFP_KERNEL);
-	if (!field->type) {
-		ret = -ENOMEM;
+	if (!field->type)
 		goto free;
-	}
+
 	seq_buf_init(&s, field->type, len);
 	if (prefix)
 		seq_buf_puts(&s, prefix);
@@ -653,6 +651,7 @@ static struct synth_field *parse_synth_field(int argc, const char **argv,
 	}
 	if (WARN_ON_ONCE(!seq_buf_buffer_left(&s)))
 		goto free;
+
 	s.buffer[s.len] = '\0';
 
 	size = synth_field_size(field->type);
@@ -666,10 +665,8 @@ static struct synth_field *parse_synth_field(int argc, const char **argv,
 
 			len = sizeof("__data_loc ") + strlen(field->type) + 1;
 			type = kzalloc(len, GFP_KERNEL);
-			if (!type) {
-				ret = -ENOMEM;
+			if (!type)
 				goto free;
-			}
 
 			seq_buf_init(&s, type, len);
 			seq_buf_puts(&s, "__data_loc ");