snapshot: conf: Enforce absolute paths on disk and memory images

RNG schema as well as the qemu driver requires absolute paths for memory
and disk snapshot image files but the XML parser was not enforcing it.
Add checks to avoid problems in qemu where the configuration it creates
is invalid.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1126329

src/conf/snapshot_conf.c

@@ -177,6 +177,16 @@ virDomainSnapshotDiskDefParseXML(xmlNodePtr node,
         }
     }
 
+    /* validate that the passed path is absolute */
+    if (virStorageSourceIsLocalStorage(def->src) &&
+        def->src->path &&
+        def->src->path[0] != '/') {
+        virReportError(VIR_ERR_XML_ERROR,
+                       _("disk snapshot image path '%s' must be absolute"),
+                       def->src->path);
+        goto cleanup;
+    }
+
     if (!def->snapshot && (def->src->path || def->src->format))
         def->snapshot = VIR_DOMAIN_SNAPSHOT_LOCATION_EXTERNAL;
 
@@ -327,6 +337,14 @@ virDomainSnapshotDefParse(xmlXPathContextPtr ctxt,
     def->file = memoryFile;
     memoryFile = NULL;
 
+    /* verify that memory path is absolute */
+    if (def->file && def->file[0] != '/') {
+        virReportError(VIR_ERR_XML_ERROR,
+                       _("memory snapshot file path (%s) must be absolute"),
+                       def->file);
+        goto cleanup;
+    }
+
     if ((n = virXPathNodeSet("./disks/*", ctxt, &nodes)) < 0)
         goto cleanup;
     if (flags & VIR_DOMAIN_SNAPSHOT_PARSE_DISKS) {