qemu: migration: Don't remember seclabel for images shared from current host

In case when the user exports images from current host and there is an
incoming migration from a remote host, security label remembering would
be possible but would attempt to remember the label allowing access to
the image as the image is already used by a VM on remote host.

To prevent remembering the wrong label, we'll skip the remembering of
the label for any shared resource, so that the code behaves identically
regardless of how the image is accessed.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>

src/qemu/qemu_migration.c

@@ -526,6 +526,66 @@ qemuMigrationDstPrepareStorage(virDomainObj *vm,
 }
 
 
+static void
+qemuMigrationDstPrepareDiskSeclabelOne(virStorageSource *src,
+                                       char *const *sharedFilesystems)
+{
+    if (!virStorageSourceIsLocalStorage(src))
+        return;
+
+    /* We care only about existing local storage */
+    if (virStorageSourceIsEmpty(src))
+        return;
+
+    /* Only paths which are on local filesystem but shared elsewhere are relevant */
+    if (!virFileIsSharedFSOverride(src->path, sharedFilesystems))
+        return;
+
+    src->seclabelSkipRemember = true;
+}
+
+
+static void
+qemuMigrationDstPrepareDiskSeclabels(virDomainObj *vm,
+                                     const char **migrate_disks,
+                                     unsigned int flags)
+{
+    qemuDomainObjPrivate *priv = vm->privateData;
+    g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(priv->driver);
+    size_t i;
+
+    /* In case when storage is exported from this host, security label
+     * remembering would behave differently compared to the host which mounts
+     * the exported filesystem. Specifically for incoming migration remembering
+     * a seclabel would remember a seclabel already allowing access to the image,
+     * which is not desired. Thus we skip remembering of seclabels for images
+     * which are local to this host but accessed in a shared way from another
+     * host.
+     */
+    if (!cfg->sharedFilesystems ||
+        cfg->sharedFilesystems[0] == NULL)
+        return;
+
+    for (i = 0; i < vm->def->ndisks; i++) {
+        virDomainDiskDef *disk = vm->def->disks[i];
+
+        /* Any storage that was migrated via NBD is technically fully local so
+         * we want seclabels remembered */
+        if (flags & (VIR_MIGRATE_NON_SHARED_DISK | VIR_MIGRATE_NON_SHARED_INC)) {
+            if (qemuMigrationAnyCopyDisk(disk, migrate_disks))
+                continue;
+        }
+
+        qemuMigrationDstPrepareDiskSeclabelOne(disk->src, cfg->sharedFilesystems);
+    }
+
+    if (vm->def->os.loader && vm->def->os.loader->nvram) {
+        qemuMigrationDstPrepareDiskSeclabelOne(vm->def->os.loader->nvram,
+                                               cfg->sharedFilesystems);
+    }
+}
+
+
 /**
  * qemuMigrationDstStartNBDServer:
  * @driver: qemu driver
@@ -3186,6 +3246,8 @@ qemuMigrationDstPrepareActive(virQEMUDriver *driver,
                                              dataFD[0])))
         goto error;
 
+    qemuMigrationDstPrepareDiskSeclabels(vm, migrate_disks, flags);
+
     if (qemuProcessPrepareDomain(driver, vm, startFlags) < 0)
         goto error;