[Libguestfs] [PATCH v2 4/5] add-domain: Pass SELinux label from guest to appliance (RHBZ#912499).

[Richard W.M. Jones]

From: "Richard W.M. Jones" <rjones at redhat.com>

When adding a domain (ie. guestfs_add_domain), read the SELinux
<label/> and <imagelabel/> from the guest and use them for the
appliance.  The appliance is statically labelled the same as the
guest, so it is able to read its disks.

However tell libvirt not to try relabelling the disks, to prevent
libvirt from disturbing the existing labels on the disks (in
particular when the libvirt connection is closed, we don't want
libvirt to try to restore some other label on the disks).
---
 src/libvirt-domain.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c
index 3f5b1ed..768ed78 100644
--- a/src/libvirt-domain.c
+++ b/src/libvirt-domain.c
@@ -20,6 +20,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <assert.h>
 
 #ifdef HAVE_LIBVIRT
@@ -42,6 +43,7 @@
 
 static xmlDocPtr get_domain_xml (guestfs_h *g, virDomainPtr dom);
 static ssize_t for_each_disk (guestfs_h *g, xmlDocPtr doc, int (*f) (guestfs_h *g, const char *filename, const char *format, int readonly, void *data), void *data);
+static int libvirt_selinux_label (guestfs_h *g, xmlDocPtr doc, char **label_rtn, char **imagelabel_rtn);
 
 static void
 ignore_errors (void *ignore, virErrorPtr ignore2)
@@ -169,6 +171,7 @@ guestfs___add_libvirt_dom (guestfs_h *g, virDomainPtr dom,
   size_t ckp;
   struct add_disk_data data;
   CLEANUP_XMLFREEDOC xmlDocPtr doc = NULL;
+  CLEANUP_FREE char *label = NULL, *imagelabel = NULL;
 
   readonly =
     optargs->bitmask & GUESTFS___ADD_LIBVIRT_DOM_READONLY_BITMASK
@@ -234,6 +237,16 @@ guestfs___add_libvirt_dom (guestfs_h *g, virDomainPtr dom,
   if ((doc = get_domain_xml (g, dom)) == NULL)
     return -1;
 
+  /* Find and pass the SELinux security label to the libvirt back end. */
+  if (libvirt_selinux_label (g, doc, &label, &imagelabel) == -1)
+    return -1;
+  if (label && imagelabel) {
+    guestfs_internal_set_libvirt_selinux_label (g, label, imagelabel);
+    guestfs_internal_set_libvirt_selinux_norelabel_disks (g, 1);
+  }
+  else
+    guestfs_internal_set_libvirt_selinux_norelabel_disks (g, 0);
+
   /* Add the disks. */
   data.optargs.bitmask = 0;
   data.readonly = readonly;
@@ -374,6 +387,66 @@ connect_live (guestfs_h *g, virDomainPtr dom)
   return guestfs_set_attach_method (g, attach_method);
 }
 
+/* Find the <seclabel/> element in the libvirt XML, and if it exists
+ * get the SELinux process label and image label from it.
+ *
+ * The reason for all this is because of sVirt:
+ * https://bugzilla.redhat.com/show_bug.cgi?id=912499#c7
+ */
+static int
+libvirt_selinux_label (guestfs_h *g, xmlDocPtr doc,
+                       char **label_rtn, char **imagelabel_rtn)
+{
+  CLEANUP_XMLXPATHFREECONTEXT xmlXPathContextPtr xpathCtx = NULL;
+  CLEANUP_XMLXPATHFREEOBJECT xmlXPathObjectPtr xpathObj = NULL;
+  xmlNodeSetPtr nodes;
+  size_t nr_nodes;
+  xmlNodePtr node, child;
+  bool gotlabel = 0, gotimagelabel = 0;
+
+  xpathCtx = xmlXPathNewContext (doc);
+  if (xpathCtx == NULL) {
+    error (g, _("unable to create new XPath context"));
+    return -1;
+  }
+
+  /* This gives us a set of all the <seclabel/> nodes, hopefully only one. */
+  xpathObj = xmlXPathEvalExpression (BAD_CAST "/domain/seclabel",
+                                     xpathCtx);
+  if (xpathObj == NULL) {
+    error (g, _("unable to evaluate XPath expression"));
+    return -1;
+  }
+
+  nodes = xpathObj->nodesetval;
+  nr_nodes = nodes->nodeNr;
+
+  if (nr_nodes == 0 || nr_nodes > 1)
+    return 0;
+
+  node = nodes->nodeTab[0];
+  if (node->type != XML_ELEMENT_NODE) {
+    error (g, _("expected <seclabel/> to be an XML element"));
+    return -1;
+  }
+
+  /* Find the <label/> and <imagelabel/> child nodes. */
+  for (child = node->children; child != NULL; child = child->next) {
+    if (!gotlabel && STREQ ((char *) child->name, "label")) {
+      /* Get the label content. */
+      *label_rtn = (char *) xmlNodeGetContent (child);
+      gotlabel = 1;
+    }
+    if (!gotimagelabel && STREQ ((char *) child->name, "imagelabel")) {
+      /* Get the imagelabel content. */
+      *imagelabel_rtn = (char *) xmlNodeGetContent (child);
+      gotimagelabel = 1;
+    }
+  }
+
+  return 0;
+}
+
 /* The callback function 'f' is called once for each disk.
  *
  * Returns number of disks, or -1 if there was an error.
-- 
1.8.1.2