fix possible NULL deref in sys/dev/usb/uhub.c

[Jacob Meuser]

at line 190, if nports == 0, 'hub' will be NULL at line 334, and
'if (hub->ports)' will be a NULL dereference.

found by Amit Kulkarni using clang.

-- 
jake...@sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org

Index: uhub.c
===================================================================
RCS file: /cvs/src/sys/dev/usb/uhub.c,v
retrieving revision 1.57
diff -u -p uhub.c
--- uhub.c      25 Jan 2011 20:03:36 -0000      1.57
+++ uhub.c      18 Feb 2011 03:33:57 -0000
@@ -331,10 +331,11 @@ uhub_attach(struct device *parent, struct device *self
  bad:
        if (sc->sc_statusbuf)
                free(sc->sc_statusbuf, M_USBDEV);
-       if (hub->ports)
-               free(hub->ports, M_USBDEV);
-       if (hub)
+       if (hub) {
+               if (hub->ports)
+                       free(hub->ports, M_USBDEV);
                free(hub, M_USBDEV);
+       }
        dev->hub = NULL;
 }