tty: ldisc: add sysctl to prevent autoloading of ldiscs
commit 7c0cca7c847e6e019d67b7d793efbbe3b947d004 upstream.
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>
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 4ab518d..3eb3f2a 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -155,6 +155,13 @@
* 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;
@@ -169,6 +176,8 @@
*/
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))
@@ -774,3 +783,41 @@
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);
+}