ksym_tracer: NIL-terminate user input filter

Make sure the user input string is NULL-terminated.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: "K.Prasad" <prasad@linux.vnet.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A52E300.7020601@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_ksym.c

@@ -264,18 +264,15 @@ static ssize_t ksym_trace_filter_write(struct file *file,
 	unsigned long ksym_addr = 0;
 	int ret, op, changed = 0;
 
-	/* Ignore echo "" > ksym_trace_filter */
-	if (count == 0)
-		return 0;
-
-	input_string = kzalloc(count, GFP_KERNEL);
+	input_string = kzalloc(count + 1, GFP_KERNEL);
 	if (!input_string)
 		return -ENOMEM;
 
 	if (copy_from_user(input_string, buffer, count)) {
 		kfree(input_string);
 		return -EFAULT;
 	}
+	input_string[count] = '\0';
 
 	ret = op = parse_ksym_trace_str(input_string, &ksymname, &ksym_addr);
 	if (ret < 0) {