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/Kconfig b/drivers/tty/Kconfig
index 9510305..fdd2860 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -455,4 +455,27 @@
help
FDC channel number to use for KGDB.
+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