security_dac: Introduce remember/recall APIs

Even though the APIs are not implemented yet, they create a
skeleton that can be filled in later.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/security/security_dac.c

@@ -184,6 +184,49 @@ virSecurityDACGetImageIds(virSecurityLabelDefPtr seclabel,
     return 0;
 }
 
+/**
+ * virSecurityDACRememberLabel:
+ * @priv: driver's private data
+ * @path: path to the file
+ * @uid: user owning the @path
+ * @gid: group owning the @path
+ *
+ * Remember the owner of @path (represented by @uid:@gid).
+ *
+ * Returns: 0 on success, -1 on failure
+ */
+static int
+virSecurityDACRememberLabel(virSecurityDACDataPtr priv ATTRIBUTE_UNUSED,
+                            const char *path ATTRIBUTE_UNUSED,
+                            uid_t uid ATTRIBUTE_UNUSED,
+                            gid_t gid ATTRIBUTE_UNUSED)
+{
+    return 0;
+}
+
+/**
+ * virSecurityDACRecallLabel:
+ * @priv: driver's private data
+ * @path: path to the file
+ * @uid: user owning the @path
+ * @gid: group owning the @path
+ *
+ * Recall the previously recorded owner for the @path. However, it may happen
+ * that @path is still in use (e.g. by another domain). In that case, 1 is
+ * returned and caller should not relabel the @path.
+ *
+ * Returns: 1 if @path is still in use (@uid and @gid not touched)
+ *          0 if @path should be restored (@uid and @gid set)
+ *         -1 on failure (@uid and @gid not touched)
+ */
+static int
+virSecurityDACRecallLabel(virSecurityDACDataPtr priv ATTRIBUTE_UNUSED,
+                          const char *path ATTRIBUTE_UNUSED,
+                          uid_t *uid ATTRIBUTE_UNUSED,
+                          gid_t *gid ATTRIBUTE_UNUSED)
+{
+    return 0;
+}
 
 static virSecurityDriverStatus
 virSecurityDACProbe(const char *virtDriver ATTRIBUTE_UNUSED)
@@ -312,7 +355,22 @@ virSecurityDACSetOwnership(virSecurityDACDataPtr priv,
                            uid_t uid,
                            gid_t gid)
 {
-    /* XXX record previous ownership */
+    struct stat sb;
+
+    if (!path && src && src->path &&
+        virStorageSourceIsLocalStorage(src))
+        path = src->path;
+
+    if (path) {
+        if (stat(path, &sb) < 0) {
+            virReportSystemError(errno, _("unable to stat: %s"), path);
+            return -1;
+        }
+
+        if (virSecurityDACRememberLabel(priv, path, sb.st_uid, sb.st_gid) < 0)
+            return -1;
+    }
+
     return virSecurityDACSetOwnershipInternal(priv, src, path, uid, gid);
 }
 
@@ -322,11 +380,26 @@ virSecurityDACRestoreSecurityFileLabelInternal(virSecurityDACDataPtr priv,
                                                virStorageSourcePtr src,
                                                const char *path)
 {
+    int rv;
+    uid_t uid = 0;  /* By default return to root:root */
+    gid_t gid = 0;
+
     VIR_INFO("Restoring DAC user and group on '%s'",
              NULLSTR(src ? src->path : path));
 
-    /* XXX recall previous ownership */
-    return virSecurityDACSetOwnershipInternal(priv, src, path, 0, 0);
+    if (!path && src && src->path &&
+        virStorageSourceIsLocalStorage(src))
+        path = src->path;
+
+    if (path) {
+        rv = virSecurityDACRecallLabel(priv, path, &uid, &gid);
+        if (rv < 0)
+            return -1;
+        if (rv > 0)
+            return 0;
+    }
+
+    return virSecurityDACSetOwnershipInternal(priv, src, path, uid, gid);
 }