security_dac: Lock metadata when running transaction

Lock all the paths we want to relabel to mutually exclude other
libvirt daemons.

The only hitch here is that directories can't be locked.
Therefore, when relabeling a directory do not lock it (this
happens only when setting up some domain private paths anyway,
e.g. huge pages directory).
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/security/security_dac.c

@@ -192,7 +192,8 @@ static int virSecurityDACRestoreFileLabelInternal(virSecurityManagerPtr mgr,
  *
  * This is the callback that runs in the same namespace as the domain we are
  * relabelling. For given transaction (@opaque) it relabels all the paths on
- * the list.
+ * the list. Depending on security manager configuration it might lock paths
+ * we will relabel.
  *
  * Returns: 0 on success
  *         -1 otherwise.
@@ -202,8 +203,26 @@ virSecurityDACTransactionRun(pid_t pid ATTRIBUTE_UNUSED,
                              void *opaque)
 {
     virSecurityDACChownListPtr list = opaque;
+    const char **paths = NULL;
+    size_t npaths = 0;
     size_t i;
     int rv = 0;
+    int ret = -1;
+
+    if (VIR_ALLOC_N(paths, list->nItems) < 0)
+        return -1;
+
+    for (i = 0; i < list->nItems; i++) {
+        const char *p = list->items[i]->path;
+
+        if (virFileIsDir(p))
+            continue;
+
+        VIR_APPEND_ELEMENT_COPY_INPLACE(paths, npaths, p);
+    }
+
+    if (virSecurityManagerMetadataLock(list->manager, paths, npaths) < 0)
+        goto cleanup;
 
     for (i = 0; i < list->nItems; i++) {
         virSecurityDACChownItemPtr item = list->items[i];
@@ -222,10 +241,19 @@ virSecurityDACTransactionRun(pid_t pid ATTRIBUTE_UNUSED,
         }
 
         if (rv < 0)
-            return -1;
+            break;
     }
 
-    return 0;
+    if (virSecurityManagerMetadataUnlock(list->manager, paths, npaths) < 0)
+        goto cleanup;
+
+    if (rv < 0)
+        goto cleanup;
+
+    ret = 0;
+ cleanup:
+    VIR_FREE(paths);
+    return ret;
 }