xhci: Don't add a virt_dev to the devs array before it's fully allocated

commit 5d9b70f7d52eb14bb37861c663bae44de9521c35 upstream.

Avoid null pointer dereference if some function is walking through the
devs array accessing members of a new virt_dev that is mid allocation.

Add the virt_dev to xhci->devs[i] _after_ the virt_device and all its
members are properly allocated.

issue found by KASAN: null-ptr-deref in xhci_find_slot_id_by_port

"Quick analysis suggests that xhci_alloc_virt_device() is not mutex
protected. If so, there is a time frame where xhci->devs[slot_id] is set
but not fully initialized. Specifically, xhci->devs[i]->udev can be NULL."

Signed-off-by: Mathias Nyman <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

drivers/usb/host/xhci-mem.c

@@ -1032,10 +1032,9 @@ int xhci_alloc_virt_device(struct xhci_hcd *xhci, int slot_id,
 		return 0;
 	}
 
-	xhci->devs[slot_id] = kzalloc(sizeof(*xhci->devs[slot_id]), flags);
-	if (!xhci->devs[slot_id])
+	dev = kzalloc(sizeof(*dev), flags);
+	if (!dev)
 		return 0;
-	dev = xhci->devs[slot_id];
 
 	/* Allocate the (output) device context that will be used in the HC. */
 	dev->out_ctx = xhci_alloc_container_ctx(xhci, XHCI_CTX_TYPE_DEVICE, flags);
@@ -1083,9 +1082,17 @@ int xhci_alloc_virt_device(struct xhci_hcd *xhci, int slot_id,
 		 &xhci->dcbaa->dev_context_ptrs[slot_id],
 		 le64_to_cpu(xhci->dcbaa->dev_context_ptrs[slot_id]));
 
+	xhci->devs[slot_id] = dev;
+
 	return 1;
 fail:
-	xhci_free_virt_device(xhci, slot_id);
+
+	if (dev->in_ctx)
+		xhci_free_container_ctx(xhci, dev->in_ctx);
+	if (dev->out_ctx)
+		xhci_free_container_ctx(xhci, dev->out_ctx);
+	kfree(dev);
+
 	return 0;
 }