releases/5.11.3/tty-implement-read_iter.patch

From e930b0ae88793fd61679f7a5d24779e05efc1d9e Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Tue, 19 Jan 2021 10:49:19 -0800
Subject: tty: implement read_iter

From: Linus Torvalds <torvalds@linux-foundation.org>

[ Upstream commit dd78b0c483e33225e0e0782b0ed887129b00f956 ]

Now that the ldisc read() function takes kernel pointers, it's fairly
straightforward to make the tty file operations use .read_iter() instead
of .read().

That automatically gives us vread() and friends, and also makes it
possible to do .splice_read() on ttys again.

Fixes: 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops")
Reported-by: Oliver Giles <ohw.giles@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/tty_io.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 0c11c65d27431..623738d8e32c8 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -142,7 +142,7 @@ LIST_HEAD(tty_drivers);			/* linked list of tty drivers */
 /* Mutex to protect creating and releasing a tty */
 DEFINE_MUTEX(tty_mutex);
 
-static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
+static ssize_t tty_read(struct kiocb *, struct iov_iter *);
 static ssize_t tty_write(struct kiocb *, struct iov_iter *);
 static __poll_t tty_poll(struct file *, poll_table *);
 static int tty_open(struct inode *, struct file *);
@@ -473,8 +473,9 @@ static void tty_show_fdinfo(struct seq_file *m, struct file *file)
 
 static const struct file_operations tty_fops = {
 	.llseek		= no_llseek,
-	.read		= tty_read,
+	.read_iter	= tty_read,
 	.write_iter	= tty_write,
+	.splice_read	= generic_file_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.poll		= tty_poll,
 	.unlocked_ioctl	= tty_ioctl,
@@ -487,8 +488,9 @@ static const struct file_operations tty_fops = {
 
 static const struct file_operations console_fops = {
 	.llseek		= no_llseek,
-	.read		= tty_read,
+	.read_iter	= tty_read,
 	.write_iter	= redirected_tty_write,
+	.splice_read	= generic_file_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.poll		= tty_poll,
 	.unlocked_ioctl	= tty_ioctl,
@@ -840,16 +842,17 @@ static void tty_update_time(struct timespec64 *time)
  * data or clears the cookie. The cookie may be something that the
  * ldisc maintains state for and needs to free.
  */
-static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct file *file,
-		char __user *buf, size_t count)
+static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty,
+		struct file *file, struct iov_iter *to)
 {
 	int retval = 0;
 	void *cookie = NULL;
 	unsigned long offset = 0;
 	char kernel_buf[64];
+	size_t count = iov_iter_count(to);
 
 	do {
-		int size, uncopied;
+		int size, copied;
 
 		size = count > sizeof(kernel_buf) ? sizeof(kernel_buf) : count;
 		size = ld->ops->read(tty, file, kernel_buf, size, &cookie, offset);
@@ -865,10 +868,9 @@ static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct
 			return size;
 		}
 
-		uncopied = copy_to_user(buf+offset, kernel_buf, size);
-		size -= uncopied;
-		offset += size;
-		count -= size;
+		copied = copy_to_iter(kernel_buf, size, to);
+		offset += copied;
+		count -= copied;
 
 		/*
 		 * If the user copy failed, we still need to do another ->read()
@@ -876,7 +878,7 @@ static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct
 		 *
 		 * But make sure size is zeroed.
 		 */
-		if (unlikely(uncopied)) {
+		if (unlikely(copied != size)) {
 			count = 0;
 			retval = -EFAULT;
 		}
@@ -903,10 +905,10 @@ static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct
  *	read calls may be outstanding in parallel.
  */
 
-static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
-			loff_t *ppos)
+static ssize_t tty_read(struct kiocb *iocb, struct iov_iter *to)
 {
 	int i;
+	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
 	struct tty_struct *tty = file_tty(file);
 	struct tty_ldisc *ld;
@@ -919,11 +921,9 @@ static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
 	/* We want to wait for the line discipline to sort out in this
 	   situation */
 	ld = tty_ldisc_ref_wait(tty);
-	if (!ld)
-		return hung_up_tty_read(file, buf, count, ppos);
 	i = -EIO;
-	if (ld->ops->read)
-		i = iterate_tty_read(ld, tty, file, buf, count);
+	if (ld && ld->ops->read)
+		i = iterate_tty_read(ld, tty, file, to);
 	tty_ldisc_deref(ld);
 
 	if (i > 0)
@@ -2945,7 +2945,7 @@ static long tty_compat_ioctl(struct file *file, unsigned int cmd,
 
 static int this_tty(const void *t, struct file *file, unsigned fd)
 {
-	if (likely(file->f_op->read != tty_read))
+	if (likely(file->f_op->read_iter != tty_read))
 		return 0;
 	return file_tty(file) != t ? 0 : fd + 1;
 }
-- 
2.27.0