[PATCH] fix null pointer dereference in xen_guest_lookup()

[Alex Williamson <alex.williamson@hp.com>]

  The latest ELF changes have a null pointer dereference bug when you
have neither an elf notes section nor a __xen_guest_string.  This patch
checks for the existence of the __xen_guest_string prior to using it.
Please apply.  Thanks,

	Alex

Signed-off-by: Alex Williamson <alex.williamson@hp.com>
---

diff -r 2bc5796fbfcc tools/libxc/xc_load_elf.c
--- a/tools/libxc/xc_load_elf.c	Sat Aug 26 14:44:47 2006 -0600
+++ b/tools/libxc/xc_load_elf.c	Sat Aug 26 16:13:10 2006 -0600
@@ -93,6 +93,9 @@ static const char *xen_guest_lookup(stru
     const char *fallback;
     const char *p;
 
+    if ( !dsi->__xen_guest_string )
+        return NULL;
+
     if ( type > sizeof(xenguest_fallbacks) )
         return NULL;
 
diff -r 2bc5796fbfcc xen/common/elf.c
--- a/xen/common/elf.c	Sat Aug 26 14:44:47 2006 -0600
+++ b/xen/common/elf.c	Sat Aug 26 16:13:10 2006 -0600
@@ -49,6 +49,9 @@ static const char *xen_guest_lookup(stru
     const char *fallback;
     const char *p;
 
+    if ( !dsi->__xen_guest_string )
+        return NULL;
+
     if ( type > sizeof(xenguest_fallbacks) )
         return NULL;