security: Introduce virSecurityManagerDomainSetPathLabelRO

This API allows drivers to separate out handling of @stdin_path
of virSecurityManagerSetAllLabel(). The thing is, the QEMU driver
uses transactions for virSecurityManagerSetAllLabel() which
relabels devices from inside of domain's namespace. This is what
we usually want. Except when resuming domain from a file. The
file is opened before any namespace is set up and the FD is
passed to QEMU to read the migration stream from. Because of
this, the file lives outside of the namespace and if it so
happens that the file is a block device (i.e. it lives under
/dev) its copy will be created in the namespace. But the FD that
is passed to QEMU points to the original living in the host and
not in the namespace. So relabeling the file inside the namespace
helps nothing.

But if we have a separate API for relabeling the restore file
then the QEMU driver can continue calling
virSecurityManagerSetAllLabel() with transactions enabled and
call this new API without transactions.

We already have an API for relabeling a single file
(virSecurityManagerDomainSetPathLabel()) but in case of SELinux
it uses @imagelabel (which allows RW access) and we want to use
@content_context (which allows RO access).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>

src/libvirt_private.syms

@@ -1525,6 +1525,7 @@ virSecurityDriverLookup;
 virSecurityManagerCheckAllLabel;
 virSecurityManagerClearSocketLabel;
 virSecurityManagerDomainSetPathLabel;
+virSecurityManagerDomainSetPathLabelRO;
 virSecurityManagerGenLabel;
 virSecurityManagerGetBaseLabel;
 virSecurityManagerGetDOI;

src/security/security_driver.h

@@ -140,6 +140,9 @@ typedef int (*virSecurityDomainSetPathLabel) (virSecurityManagerPtr mgr,
                                               virDomainDefPtr def,
                                               const char *path,
                                               bool allowSubtree);
+typedef int (*virSecurityDomainSetPathLabelRO) (virSecurityManagerPtr mgr,
+                                                virDomainDefPtr def,
+                                                const char *path);
 typedef int (*virSecurityDomainSetChardevLabel) (virSecurityManagerPtr mgr,
                                                  virDomainDefPtr def,
                                                  virDomainChrSourceDefPtr dev_source,
@@ -211,6 +214,7 @@ struct _virSecurityDriver {
     virSecurityDriverGetBaseLabel getBaseLabel;
 
     virSecurityDomainSetPathLabel domainSetPathLabel;
+    virSecurityDomainSetPathLabelRO domainSetPathLabelRO;
 
     virSecurityDomainSetChardevLabel domainSetSecurityChardevLabel;
     virSecurityDomainRestoreChardevLabel domainRestoreSecurityChardevLabel;

src/security/security_manager.c

@@ -1077,6 +1077,35 @@ virSecurityManagerDomainSetPathLabel(virSecurityManagerPtr mgr,
 }
 
 
+/**
+ * virSecurityManagerDomainSetPathLabelRO:
+ * @mgr: security manager object
+ * @vm: domain definition object
+ * @path: path to label
+ *
+ * This function relabels given @path for read only access, which
+ * is in contrast with virSecurityManagerDomainSetPathLabel() which
+ * gives read write access.
+ *
+ * Returns: 0 on success, -1 on error.
+ */
+int
+virSecurityManagerDomainSetPathLabelRO(virSecurityManagerPtr mgr,
+                                       virDomainDefPtr vm,
+                                       const char *path)
+{
+    if (mgr->drv->domainSetPathLabelRO) {
+        int ret;
+        virObjectLock(mgr);
+        ret = mgr->drv->domainSetPathLabelRO(mgr, vm, path);
+        virObjectUnlock(mgr);
+        return ret;
+    }
+
+    return 0;
+}
+
+
 /**
  * virSecurityManagerSetMemoryLabel:
  * @mgr: security manager object

src/security/security_manager.h

@@ -189,6 +189,10 @@ int virSecurityManagerDomainSetPathLabel(virSecurityManagerPtr mgr,
                                          const char *path,
                                          bool allowSubtree);
 
+int virSecurityManagerDomainSetPathLabelRO(virSecurityManagerPtr mgr,
+                                           virDomainDefPtr vm,
+                                           const char *path);
+
 int virSecurityManagerSetChardevLabel(virSecurityManagerPtr mgr,
                                       virDomainDefPtr def,
                                       virDomainChrSourceDefPtr dev_source,

src/security/security_stack.c

@@ -825,6 +825,26 @@ virSecurityStackDomainSetPathLabel(virSecurityManagerPtr mgr,
     return rc;
 }
 
+
+static int
+virSecurityStackDomainSetPathLabelRO(virSecurityManagerPtr mgr,
+                                     virDomainDefPtr vm,
+                                     const char *path)
+{
+    virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
+    virSecurityStackItemPtr item = priv->itemsHead;
+    int rc = 0;
+
+    for (; item; item = item->next) {
+        if (virSecurityManagerDomainSetPathLabelRO(item->securityManager,
+                                                   vm, path) < 0)
+            rc = -1;
+    }
+
+    return rc;
+}
+
+
 static int
 virSecurityStackDomainSetChardevLabel(virSecurityManagerPtr mgr,
                                       virDomainDefPtr def,
@@ -985,6 +1005,7 @@ virSecurityDriver virSecurityDriverStack = {
     .getBaseLabel                       = virSecurityStackGetBaseLabel,
 
     .domainSetPathLabel                 = virSecurityStackDomainSetPathLabel,
+    .domainSetPathLabelRO               = virSecurityStackDomainSetPathLabelRO,
 
     .domainSetSecurityChardevLabel      = virSecurityStackDomainSetChardevLabel,
     .domainRestoreSecurityChardevLabel  = virSecurityStackDomainRestoreChardevLabel,