kprobes: Use helper to parse boolean input from userspace

The "enabled" file provides a debugfs interface to arm / disarm
kprobes in the kernel. In order to parse the buffer containing the
values written from userspace, the callback manually parses the user
input to convert it to a boolean value.

As taking a string value from userspace and converting it to boolean
is a common operation, a helper kstrtobool_from_user() is already
available in the kernel. Update the callback to use the common helper
to parse the write buffer from userspace.

Link: https://lkml.kernel.org/r/163163032637.489837.10678039554832855327.stgit@devnote2Signed-off-by: Punit Agrawal <punitagrawal@gmail.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/kprobes.c

@@ -2770,30 +2770,14 @@ static ssize_t read_enabled_file_bool(struct file *file,
 static ssize_t write_enabled_file_bool(struct file *file,
 	       const char __user *user_buf, size_t count, loff_t *ppos)
 {
-	char buf[32];
-	size_t buf_size;
-	int ret = 0;
-
-	buf_size = min(count, (sizeof(buf)-1));
-	if (copy_from_user(buf, user_buf, buf_size))
-		return -EFAULT;
+	bool enable;
+	int ret;
 
-	buf[buf_size] = '\0';
-	switch (buf[0]) {
-	case 'y':
-	case 'Y':
-	case '1':
-		ret = arm_all_kprobes();
-		break;
-	case 'n':
-	case 'N':
-	case '0':
-		ret = disarm_all_kprobes();
-		break;
-	default:
-		return -EINVAL;
-	}
+	ret = kstrtobool_from_user(user_buf, count, &enable);
+	if (ret)
+		return ret;
 
+	ret = enable ? arm_all_kprobes() : disarm_all_kprobes();
 	if (ret)
 		return ret;