tracing: Check the return value of trace_get_user()

Return immediately if trace_get_user() returned failure.
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4AB86614.7020803@cn.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/trace/ftrace.c

@@ -2202,7 +2202,7 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 	struct trace_parser *parser;
 	ssize_t ret, read;
 
-	if (!cnt || cnt < 0)
+	if (!cnt)
 		return 0;
 
 	mutex_lock(&ftrace_regex_lock);
@@ -2216,7 +2216,7 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 	parser = &iter->parser;
 	read = trace_get_user(parser, ubuf, cnt, ppos);
 
-	if (trace_parser_loaded(parser) &&
+	if (read >= 0 && trace_parser_loaded(parser) &&
 	    !trace_parser_cont(parser)) {
 		ret = ftrace_process_regex(parser->buffer,
 					   parser->idx, enable);
@@ -2552,8 +2552,7 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
 		   size_t cnt, loff_t *ppos)
 {
 	struct trace_parser parser;
-	size_t read = 0;
-	ssize_t ret;
+	ssize_t read, ret;
 
 	if (!cnt || cnt < 0)
 		return 0;
@@ -2572,7 +2571,7 @@ ftrace_graph_write(struct file *file, const char __user *ubuf,
 
 	read = trace_get_user(&parser, ubuf, cnt, ppos);
 
-	if (trace_parser_loaded((&parser))) {
+	if (read >= 0 && trace_parser_loaded((&parser))) {
 		parser.buffer[parser.idx] = 0;
 
 		/* we allow only one expression at a time */

kernel/trace/trace_events.c

@@ -232,10 +232,9 @@ ftrace_event_write(struct file *file, const char __user *ubuf,
 		   size_t cnt, loff_t *ppos)
 {
 	struct trace_parser parser;
-	size_t read = 0;
-	ssize_t ret;
+	ssize_t read, ret;
 
-	if (!cnt || cnt < 0)
+	if (!cnt)
 		return 0;
 
 	ret = tracing_update_buffers();
@@ -247,7 +246,7 @@ ftrace_event_write(struct file *file, const char __user *ubuf,
 
 	read = trace_get_user(&parser, ubuf, cnt, ppos);
 
-	if (trace_parser_loaded((&parser))) {
+	if (read >= 0 && trace_parser_loaded((&parser))) {
 		int set = 1;
 
 		if (*parser.buffer == '!')