[PATCH] usb: Avoid use-after-free by flushing endpoints early in usb_set_interface()

[Mathias Nyman <mathias.nyman@linux.intel.com>]

The steps taken by usb core to set a new interface is very different from
what is done on the xHC host side.

xHC hardware will do everything in one go. One command is used to set up
new endpoints, free old endpoints, check bandwidth, and run the new
endpoints.

All this is done by xHC when usb core asks the hcd to check for
available bandwidth. At this point usb core has not yet flushed the old
endpoints, which will cause use-after-free issues in xhci driver as
queued URBs are cancelled on a re-allocated endpoint.

To resolve this add a call to usb_disable_interface() which will flush
the endpoints before calling usb_hcd_alloc_bandwidth()

Additional checks in xhci driver will also be implemented to gracefully
handle stale URB cancel on freed and re-allocated endpoints

Cc: <stable@vger.kernel.org>
Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
 drivers/usb/core/message.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 228672f..304bef2 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -1377,6 +1377,13 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
 		return -EINVAL;
 	}
 
+	/*
+	 * usb3 hosts configure the interface in usb_hcd_alloc_bandwidth,
+	 * including freeing dropped endpoint ring buffers.
+	 * Make sure the interface endpoints are flushed before that
+	 */
+	usb_disable_interface(dev, iface, false);
+
 	/* Make sure we have enough bandwidth for this alternate interface.
 	 * Remove the current alt setting and add the new alt setting.
 	 */
-- 
2.7.4