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tty: ldisc: add sysctl to prevent autoloading of ldiscs

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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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Greg Kroah-Hartman
2019-01-21 17:26:42 +01:00
parent 83b21ed0fc
commit 7c0cca7c84
3 changed files with 74 additions and 0 deletions
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47
drivers/tty/tty_ldisc.c
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@@ -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);
}