diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
index 320b7e7..7040659 100644
--- a/hw/usb/hcd-ehci.c
+++ b/hw/usb/hcd-ehci.c
@@ -2092,18 +2092,22 @@
             break;
 
         case EST_ADVANCEQUEUE:
+            assert(q != NULL);
             again = ehci_state_advqueue(q);
             break;
 
         case EST_FETCHQTD:
+            assert(q != NULL);
             again = ehci_state_fetchqtd(q);
             break;
 
         case EST_HORIZONTALQH:
+            assert(q != NULL);
             again = ehci_state_horizqh(q);
             break;
 
         case EST_EXECUTE:
+            assert(q != NULL);
             again = ehci_state_execute(q);
             if (async) {
                 ehci->async_stepdown = 0;
diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index 92f2eee..5fb0c48 100644
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -1197,6 +1197,7 @@
             ep = epctx->transfers[xferi].packet.ep;
         }
         killed += xhci_ep_nuke_one_xfer(&epctx->transfers[xferi]);
+        epctx->transfers[xferi].packet.ep = NULL;
         xferi = (xferi + 1) % TD_QUEUE;
     }
     if (ep) {
@@ -2198,6 +2199,28 @@
     return slotid;
 }
 
+/* cleanup slot state on usb device detach */
+static void xhci_detach_slot(XHCIState *xhci, USBPort *uport)
+{
+    int slot, ep;
+
+    for (slot = 0; slot < xhci->numslots; slot++) {
+        if (xhci->slots[slot].uport == uport) {
+            break;
+        }
+    }
+    if (slot == xhci->numslots) {
+        return;
+    }
+
+    for (ep = 0; ep < 31; ep++) {
+        if (xhci->slots[slot].eps[ep]) {
+            xhci_ep_nuke_xfers(xhci, slot+1, ep+1);
+        }
+    }
+    xhci->slots[slot].uport = NULL;
+}
+
 static TRBCCode xhci_get_port_bandwidth(XHCIState *xhci, uint64_t pctx)
 {
     dma_addr_t ctx;
@@ -2940,6 +2963,7 @@
     XHCIState *xhci = usbport->opaque;
     XHCIPort *port = xhci_lookup_port(xhci, usbport);
 
+    xhci_detach_slot(xhci, usbport);
     xhci_port_update(port, 1);
 }
 
@@ -2971,13 +2995,8 @@
 {
     USBBus *bus = usb_bus_from_device(child);
     XHCIState *xhci = container_of(bus, XHCIState, bus);
-    int i;
 
-    for (i = 0; i < xhci->numslots; i++) {
-        if (xhci->slots[i].uport == uport) {
-            xhci->slots[i].uport = NULL;
-        }
-    }
+    xhci_detach_slot(xhci, uport);
 }
 
 static USBPortOps xhci_uport_ops = {
diff --git a/hw/usb/host-linux.c b/hw/usb/host-linux.c
index e8e6a42..ad75ce0 100644
--- a/hw/usb/host-linux.c
+++ b/hw/usb/host-linux.c
@@ -1314,7 +1314,7 @@
 
     dev->bus_num = bus_num;
     dev->addr = addr;
-    strcpy(dev->port, port);
+    pstrcpy(dev->port, sizeof(dev->port), port);
     dev->fd = fd;
 
     /* read the device description */
@@ -1760,7 +1760,7 @@
         if (f->addr > 0 && f->addr != addr) {
             continue;
         }
-        if (f->port != NULL && (port == NULL || strcmp(f->port, port) != 0)) {
+        if (f->port != NULL && strcmp(f->port, port) != 0) {
             continue;
         }