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Date: Sun, 24 Dec 2023 06:01:49 +0100
From: 
	Ahelenia =?utf-8?Q?Ziemia=C5=84ska?= <nabijaczleweli@nabijaczleweli.xyz>
Cc: Jens Axboe <axboe@kernel.dk>, Christian Brauner <brauner@kernel.org>, 
	Alexander Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jirislaby@kernel.org>, linux-serial@vger.kernel.org
Subject: [PATCH v2 13/11] tty: splice_write: disable
Message-ID: <fvxufyqixohx65lcusrkkfoxs5cnlsuv7kajv6bnngcoewsodx@tarta.nabijaczleweli.xyz>
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Given:
	cat > ttyW.c <<^D
	#define _GNU_SOURCE
	#include <fcntl.h>
	#include <stdlib.h>
	int main()
	{
		int pt =3D posix_openpt(O_RDWR);
		grantpt(pt);
		unlockpt(pt);
		int cl =3D open(ptsname(pt), O_WRONLY);
		for (;;)
			splice(0, 0, cl, 0, 128 * 1024 * 1024, 0);
	}
	^D
	cc ttyW.c -o ttyW
	mkfifo fifo
	truncate 32M 32M
	./ttyW < fifo &
	cp 32M fifo &
	sleep 0.1
	read -r _ < fifo
ttyW used to sleep in splice and the shell used to enter an
uninterruptible sleep in open("fifo");
now the splice returns -EINVAL and the whole program completes.

This is also symmetric with the splice_read removal.

Signed-off-by: Ahelenia Ziemia=C5=84ska <nabijaczleweli@nabijaczleweli.xyz>
---
It hit me that I should actually probably exhaustively re-evaluate
splice_write as well since re-evaluating splice_read went so well.

fs/fuse/dev.c:  .splice_write   =3D fuse_dev_splice_write,
drivers/char/virtio_console.c:  .splice_write =3D port_fops_splice_write,
locks, takes some pages, unlocks, writes, so OK

drivers/char/mem.c:	.splice_write	=3D splice_write_null,
drivers/char/mem.c:	.splice_write	=3D splice_write_zero,
no-op

drivers/char/random.c:	.splice_write =3D iter_file_splice_write,
drivers/char/random.c:	.splice_write =3D iter_file_splice_write,
AFAICT write_pool_user is okay to invoke like this?

net/socket.c:   .splice_write =3D splice_to_socket,
already dealt with in 11/11

drivers/tty/tty_io.c:   .splice_write   =3D iter_file_splice_write,
drivers/tty/tty_io.c:   .splice_write   =3D iter_file_splice_write,
they do lock the pipe and try the write with the lock held;
we already killed splice_read so just kill splice_write for symmetry
(13/11)

fs/fuse/file.c: .splice_write   =3D iter_file_splice_write,
same logic as splice_read applies (14/11)

 drivers/tty/tty_io.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 50c2957a9c7f..d931c34ddcbf 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -465,7 +465,6 @@ static const struct file_operations tty_fops =3D {
 	.llseek		=3D no_llseek,
 	.read_iter	=3D tty_read,
 	.write_iter	=3D tty_write,
-	.splice_write	=3D iter_file_splice_write,
 	.poll		=3D tty_poll,
 	.unlocked_ioctl	=3D tty_ioctl,
 	.compat_ioctl	=3D tty_compat_ioctl,
@@ -479,7 +478,6 @@ static const struct file_operations console_fops =3D {
 	.llseek		=3D no_llseek,
 	.read_iter	=3D tty_read,
 	.write_iter	=3D redirected_tty_write,
-	.splice_write	=3D iter_file_splice_write,
 	.poll		=3D tty_poll,
 	.unlocked_ioctl	=3D tty_ioctl,
 	.compat_ioctl	=3D tty_compat_ioctl,
--=20
2.39.2

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