2 files changed, 19 insertions, 10 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 319d68c8a5df..219e85756171 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2081,9 +2081,6 @@ static int canon_copy_from_read_buf(struct tty_struct *tty,
 	return 0;
 }
 
-extern ssize_t redirected_tty_write(struct file *, const char __user *,
-							size_t, loff_t *);
-
 /**
  *	job_control		-	check job control
  *	@tty: tty
@@ -2105,7 +2102,7 @@ static int job_control(struct tty_struct *tty, struct file *file)
 	/* NOTE: not yet done after every sleep pending a thorough
 	   check of the logic of this change. -- jlc */
 	/* don't stop on /dev/console */
-	if (file->f_op->write == redirected_tty_write)
+	if (file->f_op->write_iter == redirected_tty_write)
 		return 0;
 
 	return __tty_check_change(tty, SIGTTIN);
@@ -2309,7 +2306,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
 	ssize_t retval = 0;
 
 	/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
-	if (L_TOSTOP(tty) && file->f_op->write != redirected_tty_write) {
+	if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
 		retval = tty_check_change(tty);
 		if (retval)
 			return retval;
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 4a208a95e921..816e709afa56 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -144,10 +144,8 @@ DEFINE_MUTEX(tty_mutex);
 
 static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
 static ssize_t tty_write(struct kiocb *, struct iov_iter *);
-ssize_t redirected_tty_write(struct kiocb *, struct iov_iter *);
 static __poll_t tty_poll(struct file *, poll_table *);
 static int tty_open(struct inode *, struct file *);
-long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 #ifdef CONFIG_COMPAT
 static long tty_compat_ioctl(struct file *file, unsigned int cmd,
 				unsigned long arg);
@@ -1028,9 +1026,8 @@ void tty_write_message(struct tty_struct *tty, char *msg)
  *	write method will not be invoked in parallel for each device.
  */
 
-static ssize_t tty_write(struct kiocb *iocb, struct iov_iter *from)
+static ssize_t file_tty_write(struct file *file, struct kiocb *iocb, struct iov_iter *from)
 {
-	struct file *file = iocb->ki_filp;
 	struct tty_struct *tty = file_tty(file);
  	struct tty_ldisc *ld;
 	ssize_t ret;
@@ -1053,6 +1050,11 @@ static ssize_t tty_write(struct kiocb *iocb, struct iov_iter *from)
 	return ret;
 }
 
+static ssize_t tty_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	return file_tty_write(iocb->ki_filp, iocb, from);
+}
+
 ssize_t redirected_tty_write(struct kiocb *iocb, struct iov_iter *iter)
 {
 	struct file *p = NULL;
@@ -1062,9 +1064,13 @@ ssize_t redirected_tty_write(struct kiocb *iocb, struct iov_iter *iter)
 		p = get_file(redirect);
 	spin_unlock(&redirect_lock);
 
+	/*
+	 * We know the redirected tty is just another tty, we can can
+	 * call file_tty_write() directly with that file pointer.
+	 */
 	if (p) {
 		ssize_t res;
-		res = vfs_iocb_iter_write(p, iocb, iter);
+		res = file_tty_write(p, iocb, iter);
 		fput(p);
 		return res;
 	}
@@ -2310,6 +2316,12 @@ static int tioccons(struct file *file)
 			fput(f);
 		return 0;
 	}
+	if (file->f_op->write_iter != tty_write)
+		return -ENOTTY;
+	if (!(file->f_mode & FMODE_WRITE))
+		return -EBADF;
+	if (!(file->f_mode & FMODE_CAN_WRITE))
+		return -EINVAL;
 	spin_lock(&redirect_lock);
 	if (redirect) {
 		spin_unlock(&redirect_lock);