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Commit 7c0cca7c authored by Greg Kroah-Hartman's avatar Greg Kroah-Hartman
Browse files

tty: ldisc: add sysctl to prevent autoloading of ldiscs 



By default, the kernel will automatically load the module of any line
dicipline that is asked for.  As this sometimes isn't the safest thing
to do, provide a sysctl to disable this feature.

By default, we set this to 'y' as that is the historical way that Linux
has worked, and we do not want to break working systems.  But in the
future, perhaps this can default to 'n' to prevent this functionality.

Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: default avatarTheodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 83b21ed0

drivers/tty/Kconfig

+24 −0
Original line number Diff line number Diff line
@@ -441,4 +441,28 @@ config VCC 
	depends on SUN_LDOMS

	help

	  Support for Sun logical domain consoles.



config LDISC_AUTOLOAD

	bool "Automatically load TTY Line Disciplines"

	default y

	help

	  Historically the kernel has always automatically loaded any

	  line discipline that is in a kernel module when a user asks

	  for it to be loaded with the TIOCSETD ioctl, or through other

	  means.  This is not always the best thing to do on systems

	  where you know you will not be using some of the more

	  "ancient" line disciplines, so prevent the kernel from doing

	  this unless the request is coming from a process with the

	  CAP_SYS_MODULE permissions.



	  Say 'Y' here if you trust your userspace users to do the right

	  thing, or if you have only provided the line disciplines that

	  you know you will be using, or if you wish to continue to use

	  the traditional method of on-demand loading of these modules

	  by any user.



	  This functionality can be changed at runtime with the

	  dev.tty.ldisc_autoload sysctl, this configuration option will

	  only set the default value of this functionality.



endif # TTY

drivers/tty/tty_io.c

+3 −0
Original line number Diff line number Diff line
@@ -513,6 +513,8 @@ static const struct file_operations hung_up_tty_fops = { 
static DEFINE_SPINLOCK(redirect_lock);

static struct file *redirect;



extern void tty_sysctl_init(void);



/**

 *	tty_wakeup	-	request more data

 *	@tty: terminal
@@ -3483,6 +3485,7 @@ void console_sysfs_notify(void) 
 */

int __init tty_init(void)

{

	tty_sysctl_init();

	cdev_init(&tty_cdev, &tty_fops);

	if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||

	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)

drivers/tty/tty_ldisc.c

+47 −0
Original line number Diff line number Diff line
@@ -156,6 +156,13 @@ static void put_ldops(struct tty_ldisc_ops *ldops) 
 *		takes tty_ldiscs_lock to guard against ldisc races

 */



#if defined(CONFIG_LDISC_AUTOLOAD)

	#define INITIAL_AUTOLOAD_STATE	1

#else

	#define INITIAL_AUTOLOAD_STATE	0

#endif

static int tty_ldisc_autoload = INITIAL_AUTOLOAD_STATE;



static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)

{

	struct tty_ldisc *ld;
@@ -170,6 +177,8 @@ static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc) 
	 */

	ldops = get_ldops(disc);

	if (IS_ERR(ldops)) {

		if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)

			return ERR_PTR(-EPERM);

		request_module("tty-ldisc-%d", disc);

		ldops = get_ldops(disc);

		if (IS_ERR(ldops))
@@ -845,3 +854,41 @@ void tty_ldisc_deinit(struct tty_struct *tty) 
		tty_ldisc_put(tty->ldisc);

	tty->ldisc = NULL;

}



static int zero;

static int one = 1;

static struct ctl_table tty_table[] = {

	{

		.procname	= "ldisc_autoload",

		.data		= &tty_ldisc_autoload,

		.maxlen		= sizeof(tty_ldisc_autoload),

		.mode		= 0644,

		.proc_handler	= proc_dointvec,

		.extra1		= &zero,

		.extra2		= &one,

	},

	{ }

};



static struct ctl_table tty_dir_table[] = {

	{

		.procname	= "tty",

		.mode		= 0555,

		.child		= tty_table,

	},

	{ }

};



static struct ctl_table tty_root_table[] = {

	{

		.procname	= "dev",

		.mode		= 0555,

		.child		= tty_dir_table,

	},

	{ }

};



void tty_sysctl_init(void)

{

	register_sysctl_table(tty_root_table);

}