libxc: Verify Magic number when reading dump

The xen core files record a magic number, 
but when they are loaded it isn't checked.
This patch resolves this.

Signed-Off-By: Horms <horms@verge.net.au>

tools/libxc/xc_core.c

@@ -61,7 +61,7 @@ xc_domain_dumpcore(int xc_handle,
  
     nr_pages = info.nr_pages;
 
-    header.xch_magic = 0xF00FEBED; 
+    header.xch_magic = XC_CORE_MAGIC;
     header.xch_nr_vcpus = nr_vcpus;
     header.xch_nr_pages = nr_pages;
     header.xch_ctxt_offset = sizeof(struct xc_core_header);

tools/libxc/xc_ptrace_core.c

@@ -111,6 +111,13 @@ xc_waitdomain_core(
         if (read(domfd, &header, sizeof(header)) != sizeof(header))
             return -1;
 
+        if (header.xch_magic != XC_CORE_MAGIC) {
+                printf("Magic number missmatch: 0x%08x (file) != "
+                                        " 0x%08x (code)\n", header.xch_magic,
+                                        XC_CORE_MAGIC);
+                return -1;
+        }
+
         nr_pages = header.xch_nr_pages;
         nr_vcpus = header.xch_nr_vcpus;
         pages_offset = header.xch_pages_offset;

tools/libxc/xenctrl.h

@@ -92,6 +92,7 @@ typedef struct xc_core_header {
     unsigned int xch_pages_offset;
 } xc_core_header_t;
 
+#define XC_CORE_MAGIC 0xF00FEBED
 
 long xc_ptrace_core(
     int xc_handle,