| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-Id: <20190403113327.3628-1-vincent.whitchurch@axis.com>
Date: Wed, 3 Apr 2019 13:33:27 +0200
From: Vincent Whitchurch <vincent.whitchurch@...s.com>
To: gregkh@...uxfoundation.org, jslaby@...e.com
Cc: linux-kernel@...r.kernel.org, Vincent Whitchurch <rabinv@...s.com>
Subject: [PATCH] tty: Add NULL TTY driver
If no console driver is enabled (or if a non-present driver is selected
with something like console=null in an attempt to disable the console),
opening /dev/console errors out, and init scripts and other userspace
code that relies on the existence of a console will fail. Symlinking
/dev/null to /dev/console does not solve the problem since /dev/null
does not behave like a real TTY.
To just provide a dummy console to userspace when no console driver is
available or desired, add a ttynull driver which simply discards all
writes. It can be chosen on the command line in the standard way, i.e.
with console=ttynull.
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
---
drivers/tty/Kconfig | 14 ++++++
drivers/tty/Makefile | 1 +
drivers/tty/ttynull.c | 109 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 124 insertions(+)
create mode 100644 drivers/tty/ttynull.c
diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index e0a04bfc873e..d862f442f389 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -376,6 +376,20 @@ config PPC_EARLY_DEBUG_EHV_BC_HANDLE
there simply will be no early console output. This is true also
if you don't boot under a hypervisor at all.
+config NULL_TTY
+ tristate "NULL TTY driver"
+ help
+ Say Y here if you want a NULL TTY which simply discards messages.
+
+ This is useful to allow userspace applications which expect a console
+ device to work without modifications even when no console is
+ available or desired.
+
+ In order to use this driver, you should redirect the console to this
+ TTY, or boot the kernel with console=ttynull.
+
+ If unsure, say N.
+
config GOLDFISH_TTY
tristate "Goldfish TTY Driver"
depends on GOLDFISH
diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index c72cafdf32b4..020b1cd9294f 100644
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_ISI) += isicom.o
obj-$(CONFIG_MOXA_INTELLIO) += moxa.o
obj-$(CONFIG_MOXA_SMARTIO) += mxser.o
obj-$(CONFIG_NOZOMI) += nozomi.o
+obj-$(CONFIG_NULL_TTY) += ttynull.o
obj-$(CONFIG_ROCKETPORT) += rocket.o
obj-$(CONFIG_SYNCLINK_GT) += synclink_gt.o
obj-$(CONFIG_SYNCLINKMP) += synclinkmp.o
diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c
new file mode 100644
index 000000000000..17f05b7eb6d3
--- /dev/null
+++ b/drivers/tty/ttynull.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 Axis Communications AB
+ *
+ * Based on ttyprintk.c:
+ * Copyright (C) 2010 Samo Pogacnik
+ */
+
+#include <linux/console.h>
+#include <linux/module.h>
+#include <linux/tty.h>
+
+static const struct tty_port_operations ttynull_port_ops;
+static struct tty_driver *ttynull_driver;
+static struct tty_port ttynull_port;
+
+static int ttynull_open(struct tty_struct *tty, struct file *filp)
+{
+ return tty_port_open(&ttynull_port, tty, filp);
+}
+
+static void ttynull_close(struct tty_struct *tty, struct file *filp)
+{
+ tty_port_close(&ttynull_port, tty, filp);
+}
+
+static void ttynull_hangup(struct tty_struct *tty)
+{
+ tty_port_hangup(&ttynull_port);
+}
+
+static int ttynull_write(struct tty_struct *tty, const unsigned char *buf,
+ int count)
+{
+ return count;
+}
+
+static int ttynull_write_room(struct tty_struct *tty)
+{
+ return 65536;
+}
+
+static const struct tty_operations ttynull_ops = {
+ .open = ttynull_open,
+ .close = ttynull_close,
+ .hangup = ttynull_hangup,
+ .write = ttynull_write,
+ .write_room = ttynull_write_room,
+};
+
+static struct tty_driver *ttynull_device(struct console *c, int *index)
+{
+ *index = 0;
+ return ttynull_driver;
+}
+
+static struct console ttynull_console = {
+ .name = "ttynull",
+ .device = ttynull_device,
+};
+
+static int __init ttynull_init(void)
+{
+ struct tty_driver *driver;
+ int ret;
+
+ driver = tty_alloc_driver(1,
+ TTY_DRIVER_RESET_TERMIOS |
+ TTY_DRIVER_REAL_RAW |
+ TTY_DRIVER_UNNUMBERED_NODE);
+ if (IS_ERR(driver))
+ return PTR_ERR(driver);
+
+ tty_port_init(&ttynull_port);
+ ttynull_port.ops = &ttynull_port_ops;
+
+ driver->driver_name = "ttynull";
+ driver->name = "ttynull";
+ driver->type = TTY_DRIVER_TYPE_CONSOLE;
+ driver->init_termios = tty_std_termios;
+ driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET;
+ tty_set_operations(driver, &ttynull_ops);
+ tty_port_link_device(&ttynull_port, driver, 0);
+
+ ret = tty_register_driver(driver);
+ if (ret < 0) {
+ put_tty_driver(driver);
+ tty_port_destroy(&ttynull_port);
+ return ret;
+ }
+
+ ttynull_driver = driver;
+ register_console(&ttynull_console);
+
+ return 0;
+}
+
+static void __exit ttynull_exit(void)
+{
+ unregister_console(&ttynull_console);
+ tty_unregister_driver(ttynull_driver);
+ put_tty_driver(ttynull_driver);
+ tty_port_destroy(&ttynull_port);
+}
+
+module_init(ttynull_init);
+module_exit(ttynull_exit);
+
+MODULE_LICENSE("GPL v2");
--
2.20.0
Powered by blists - more mailing lists