[PATCH 19/24] security: usbgadget: add usbgadget security policy

[Sascha Hauer <s.hauer@pengutronix.de>]

USB gadget might be considered dangerous in secure environments, so add
a security policy for it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 Sconfig                            |  1 +
 common/usbgadget.c                 | 26 ++++++++++++++++++++++++++
 drivers/usb/gadget/Sconfig         | 11 +++++++++++
 drivers/usb/gadget/composite.c     |  4 ++++
 drivers/usb/gadget/legacy/serial.c |  4 ++++
 5 files changed, 46 insertions(+)

diff --git a/Sconfig b/Sconfig
index 899a1fb5783fb79def32e5af160b39208fea2edc..878d5055af2967617219cbadbfd8bee3f85236bd 100644
--- a/Sconfig
+++ b/Sconfig
@@ -6,4 +6,5 @@ source "scripts/Sconfig.include"
 
 source "security/Sconfig"
 source "common/Sconfig"
+source "drivers/usb/gadget/Sconfig"
 source "commands/Sconfig"
diff --git a/common/usbgadget.c b/common/usbgadget.c
index 1333eaa413eafb766dc74e37e14d5082e93879ac..dc7b3ddc808ee0b1c63d81b914ff915bcc92a863 100644
--- a/common/usbgadget.c
+++ b/common/usbgadget.c
@@ -18,6 +18,7 @@
 #include <globalvar.h>
 #include <magicvar.h>
 #include <system-partitions.h>
+#include <security/config.h>
 
 static int autostart;
 static int nv_loaded;
@@ -81,6 +82,9 @@ int usbgadget_register(struct f_multi_opts *opts)
 	int ret;
 	struct device *dev;
 
+	if (!IS_ALLOWED(SCONFIG_USB_GADGET))
+		return -EPERM;
+
 	/*
 	 * Creating a gadget with both DFU and Fastboot may not work.
 	 * fastboot 1:8.1.0+r23-5 can deal with it, but dfu-util 0.9
@@ -106,6 +110,9 @@ int usbgadget_prepare_register(const struct usbgadget_funcs *funcs)
 	struct f_multi_opts *opts;
 	int ret;
 
+	if (!IS_ALLOWED(SCONFIG_USB_GADGET))
+		return -EPERM;
+
 	opts = usbgadget_prepare(funcs);
 	if (IS_ERR(opts))
 		return PTR_ERR(opts);
@@ -161,6 +168,21 @@ void usbgadget_autostart(bool enable)
 	usbgadget_do_autostart();
 }
 
+static void usbgadget_sconfig_update(struct sconfig_notifier_block *nb,
+				     enum security_config_option opt,
+				     bool allowed)
+{
+        if (allowed) {
+		if (autostart)
+			usbgadget_do_autostart();
+	} else {
+		usb_multi_unregister();
+		usb_serial_unregister();
+	}
+}
+
+static struct sconfig_notifier_block sconfig_notifier;
+
 static int usbgadget_globalvars_init(void)
 {
 	globalvar_add_simple_bool("usbgadget.acm", &acm);
@@ -169,6 +191,10 @@ static int usbgadget_globalvars_init(void)
 		globalvar_add_bool("usbgadget.autostart", usbgadget_autostart_set,
 				   &autostart, NULL);
 
+	sconfig_register_handler_filtered(&sconfig_notifier,
+                                          usbgadget_sconfig_update,
+                                          SCONFIG_USB_GADGET);
+
 	return 0;
 }
 coredevice_initcall(usbgadget_globalvars_init);
diff --git a/drivers/usb/gadget/Sconfig b/drivers/usb/gadget/Sconfig
new file mode 100644
index 0000000000000000000000000000000000000000..38797301e514c203f75f876fa54971846d39d292
--- /dev/null
+++ b/drivers/usb/gadget/Sconfig
@@ -0,0 +1,11 @@
+
+menu "USB Gadget Policy"
+
+config USB_GADGET
+	bool "Allow USB gadget"
+	depends on $(kconfig-enabled,USB_GADGET)
+	help
+	  USB gadget support might be potentially dangerous in secure environments.
+	  The DFU and fastboot protocols allow to modify system partitions.
+
+endmenu
diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 98f7b5bf7fb412b77f8a926375df3f0ffbbc96da..2a9984e37ad3ec1325822eb2d328481ceb3ff906 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -15,6 +15,7 @@
 #include <linux/usb/composite.h>
 #include <linux/bitfield.h>
 #include <linux/uuid.h>
+#include <security/config.h>
 #include <asm/unaligned.h>
 #include <asm/byteorder.h>
 
@@ -2489,6 +2490,9 @@ int usb_composite_probe(struct usb_composite_driver *driver)
 {
 	struct usb_gadget_driver *gadget_driver;
 
+	if (!IS_ALLOWED(SCONFIG_USB_GADGET))
+		return -EPERM;
+
 	if (!driver || !driver->dev || !driver->bind)
 		return -EINVAL;
 
diff --git a/drivers/usb/gadget/legacy/serial.c b/drivers/usb/gadget/legacy/serial.c
index 913d174a917794e7cab0f8006b8fd814887029f4..700e9db3a57462e331936efd303c6614544b251a 100644
--- a/drivers/usb/gadget/legacy/serial.c
+++ b/drivers/usb/gadget/legacy/serial.c
@@ -15,6 +15,7 @@
 #include <linux/usb/gadget.h>
 #include <linux/usb/composite.h>
 #include <linux/usb/usbserial.h>
+#include <security/config.h>
 #include <asm/byteorder.h>
 
 #include "u_serial.h"
@@ -253,6 +254,9 @@ int usb_serial_register(struct usb_serial_pdata *pdata)
 {
 	int ret;
 
+	if (!IS_ALLOWED(SCONFIG_USB_GADGET))
+		return -EPERM;
+
 	if (usb_serial_registered) {
 		pr_err("USB serial gadget already registered\n");
 		return -EBUSY;

-- 
2.39.5