Patch "usb: gadget: composite: Fix use-after-free in usb_composite_overwrite_options" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

usb: gadget: composite: Fix use-after-free in usb_composite_overwrite_options

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-gadget-composite-fix-use-after-free-in-usb_composite_overwrite_options.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andrew Gabbasov <[email protected]>
Date: Sat, 30 Sep 2017 08:55:55 -0700
Subject: usb: gadget: composite: Fix use-after-free in usb_composite_overwrite_options

From: Andrew Gabbasov <[email protected]>

commit aec17e1e249567e82b26dafbb86de7d07fde8729 upstream.

KASAN enabled configuration reports an error

    BUG: KASAN: use-after-free in usb_composite_overwrite_options+...
                [libcomposite] at addr ...
    Read of size 1 by task ...

when some driver is un-bound and then bound again.
For example, this happens with FunctionFS driver when "ffs-test" test application is run several times in a row.

If the driver has empty manufacturer ID string in initial static data, it is then replaced with generated string. After driver unbinding the generated string is freed, but the driver data still keep that pointer. And if the driver is then bound again, that pointer is re-used for string emptiness check.

The fix is to clean up the driver string data upon its unbinding to drop the pointer to freed memory.

---
 drivers/usb/gadget/composite.c |    5 +++++
 1 file changed, 5 insertions(+)

@@ -1806,6 +1806,8 @@ static DEVICE_ATTR_RO(suspended);
 static void __composite_unbind(struct usb_gadget *gadget, bool unbind_driver)
 {
 	struct usb_composite_dev	*cdev = get_gadget_data(gadget);
+	struct usb_gadget_strings	*gstr = cdev->driver->strings[0];
+	struct usb_string		*dev_str = gstr->strings;
 
 	/* composite_disconnect() must already have been called
 	 * by the underlying peripheral controller driver!

@@ -1825,6 +1827,9 @@ static void __composite_unbind(struct us
 
 	composite_dev_cleanup(cdev);
 
+	if (dev_str[USB_GADGET_MANUFACTURER_IDX].s == cdev->def_manufacturer)
+		dev_str[USB_GADGET_MANUFACTURER_IDX].s = "";
+
 	kfree(cdev->def_manufacturer);
 	kfree(cdev);
 	set_gadget_data(gadget, NULL);

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/usb-gadget-composite-fix-use-after-free-in-usb_composite_overwrite_options.patch