[PATCH v3] usb: devio: Add ioctl to disallow detaching kernel USB drivers.

[Emilio LÃpez]

From: Reilly Grant <reillyg@xxxxxxxxxxxx>

The new USBDEVFS_DROP_PRIVILEGES ioctl allows a process to voluntarily
relinquish the ability to issue other ioctls that may interfere with
other processes and drivers that have claimed an interface on the
device.

Signed-off-by: Reilly Grant <reillyg@xxxxxxxxxxxx>
Signed-off-by: Emilio LÃpez <emilio.lopez@xxxxxxxxxxxxxxx>

---

Changes in v3:
- Switch ioctl to use a __u32 given the iface qty is capped at 32
- Reword comments as requested by Alan
- Allow callers to shrink the allowed interfaces mask

Changes in v2:
- Added a parameter to the ioctl, a mask of interfaces an unprivileged
  process is allowed to claim.
- Drop Tested-by's

 drivers/usb/core/devio.c          | 59 ++++++++++++++++++++++++++++++++++++---
 include/uapi/linux/usbdevice_fs.h |  1 +
 2 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 59e7a33..3750255 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -77,6 +77,8 @@ struct usb_dev_state {
 	unsigned long ifclaimed;
 	u32 secid;
 	u32 disabled_bulk_eps;
+	bool privileges_dropped;
+	unsigned long interface_allowed_mask;
 };
 
 struct async {
@@ -624,6 +626,10 @@ static int claimintf(struct usb_dev_state *ps, unsigned int ifnum)
 	if (test_bit(ifnum, &ps->ifclaimed))
 		return 0;
 
+	if (ps->privileges_dropped
+	 && !test_bit(ifnum, &ps->interface_allowed_mask))
+		return -EACCES;
+
 	intf = usb_ifnum_to_if(dev, ifnum);
 	if (!intf)
 		err = -ENOENT;
@@ -861,7 +867,7 @@ static int usbdev_open(struct inode *inode, struct file *file)
 	int ret;
 
 	ret = -ENOMEM;
-	ps = kmalloc(sizeof(struct usb_dev_state), GFP_KERNEL);
+	ps = kzalloc(sizeof(struct usb_dev_state), GFP_KERNEL);
 	if (!ps)
 		goto out_free_ps;
 
@@ -889,16 +895,14 @@ static int usbdev_open(struct inode *inode, struct file *file)
 
 	ps->dev = dev;
 	ps->file = file;
+	ps->interface_allowed_mask = 0xFFFFFFFF; /* 32 bits */
 	spin_lock_init(&ps->lock);
 	INIT_LIST_HEAD(&ps->list);
 	INIT_LIST_HEAD(&ps->async_pending);
 	INIT_LIST_HEAD(&ps->async_completed);
 	init_waitqueue_head(&ps->wait);
-	ps->discsignr = 0;
 	ps->disc_pid = get_pid(task_pid(current));
 	ps->cred = get_current_cred();
-	ps->disccontext = NULL;
-	ps->ifclaimed = 0;
 	security_task_getsecid(current, &ps->secid);
 	smp_wmb();
 	list_add_tail(&ps->list, &dev->filelist);
@@ -1198,6 +1202,27 @@ static int proc_connectinfo(struct usb_dev_state *ps, void __user *arg)
 
 static int proc_resetdevice(struct usb_dev_state *ps)
 {
+	struct usb_host_config *actconfig = ps->dev->actconfig;
+	struct usb_interface *interface;
+	int i, number;
+
+	/* Don't allow a device reset if the process has dropped the
+	 * privilege to do such things and any of the interfaces are
+	 * currently claimed.
+	 */
+	if (ps->privileges_dropped && actconfig) {
+		for (i = 0; i < actconfig->desc.bNumInterfaces; ++i) {
+			interface = actconfig->interface[i];
+			number = interface->cur_altsetting->desc.bInterfaceNumber;
+			if (usb_interface_claimed(interface)) {
+				dev_warn(&ps->dev->dev,
+					"usbfs: interface %d claimed by %s while '%s' resets device\n",
+					number,	interface->dev.driver->name, current->comm);
+				return -EACCES;
+			}
+		}
+	}
+
 	return usb_reset_device(ps->dev);
 }
 
@@ -1915,6 +1940,9 @@ static int proc_ioctl(struct usb_dev_state *ps, struct usbdevfs_ioctl *ctl)
 	struct usb_interface    *intf = NULL;
 	struct usb_driver       *driver = NULL;
 
+	if (ps->privileges_dropped)
+		return -EACCES;
+
 	/* alloc buffer */
 	size = _IOC_SIZE(ctl->ioctl_code);
 	if (size > 0) {
@@ -2067,6 +2095,9 @@ static int proc_disconnect_claim(struct usb_dev_state *ps, void __user *arg)
 	if (intf->dev.driver) {
 		struct usb_driver *driver = to_usb_driver(intf->dev.driver);
 
+		if (ps->privileges_dropped)
+			return -EACCES;
+
 		if ((dc.flags & USBDEVFS_DISCONNECT_CLAIM_IF_DRIVER) &&
 				strncmp(dc.driver, intf->dev.driver->name,
 					sizeof(dc.driver)) != 0)
@@ -2123,6 +2154,23 @@ static int proc_free_streams(struct usb_dev_state *ps, void __user *arg)
 	return r;
 }
 
+static int proc_drop_privileges(struct usb_dev_state *ps, void __user *arg)
+{
+	u32 data;
+
+	if (copy_from_user(&data, arg, sizeof(data)))
+		return -EFAULT;
+
+	/* This is an one way operation. Once privileges are
+	 * dropped, you cannot regain them. You may however reissue
+	 * this ioctl to shrink the allowed interfaces mask.
+	 */
+	ps->interface_allowed_mask &= data;
+	ps->privileges_dropped = true;
+
+	return 0;
+}
+
 /*
  * NOTE:  All requests here that have interface numbers as parameters
  * are assuming that somehow the configuration has been prevented from
@@ -2311,6 +2359,9 @@ static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
 	case USBDEVFS_FREE_STREAMS:
 		ret = proc_free_streams(ps, p);
 		break;
+	case USBDEVFS_DROP_PRIVILEGES:
+		ret = proc_drop_privileges(ps, p);
+		break;
 	}
 
  done:
diff --git a/include/uapi/linux/usbdevice_fs.h b/include/uapi/linux/usbdevice_fs.h
index 019ba1e..2fad9f85 100644
--- a/include/uapi/linux/usbdevice_fs.h
+++ b/include/uapi/linux/usbdevice_fs.h
@@ -187,5 +187,6 @@ struct usbdevfs_streams {
 #define USBDEVFS_DISCONNECT_CLAIM  _IOR('U', 27, struct usbdevfs_disconnect_claim)
 #define USBDEVFS_ALLOC_STREAMS     _IOR('U', 28, struct usbdevfs_streams)
 #define USBDEVFS_FREE_STREAMS      _IOR('U', 29, struct usbdevfs_streams)
+#define USBDEVFS_DROP_PRIVILEGES   _IOR('U', 30, __u32)
 
 #endif /* _UAPI_LINUX_USBDEVICE_FS_H */
-- 
2.5.0