Re: [syzbot] [isdn4linux?] [nilfs?] INFO: task hung in mISDN_ioctl

[Edward Adam Davis]

#syz test

diff --git a/drivers/isdn/mISDN/timerdev.c b/drivers/isdn/mISDN/timerdev.c
index 7cfa8c61dba0..0c3771a5cd0b 100644
--- a/drivers/isdn/mISDN/timerdev.c
+++ b/drivers/isdn/mISDN/timerdev.c
@@ -238,8 +238,13 @@ mISDN_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 			ret = id;
 			break;
 		}
-		if (put_user(id, (int __user *)arg))
+		if (!user_write_access_begin((int __user *)arg, sizeof(int))) {
 			ret = -EFAULT;
+			break;
+		}
+
+		unsafe_put_user(id, (int __user *)arg, Efault);
+		user_write_access_end();
 		break;
 	case IMDELTIMER:
 		if (get_user(id, (int __user *)arg)) {
@@ -255,8 +260,13 @@ mISDN_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 	default:
 		ret = -EINVAL;
 	}
+out:
 	mutex_unlock(&mISDN_mutex);
 	return ret;
+Efault:
+	user_write_access_end();
+	ret = -EFAULT;
+	goto out;
 }
 
 static const struct file_operations mISDN_fops = {