security: Introduce VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP flag

Our decision whether to remember seclabel for a disk image
depends on a few factors. If the image is readonly or shared or
not the chain top the remembering is suppressed for the image.
However, the virSecurityManagerSetImageLabel() is too low level
to determine whether passed @src is chain top or not. Even though
the function has the @parent argument it does not necessarily
reflect the chain top - it only points to the top level image in
the chain we want to relabel and not to the topmost image of the
whole chain. And this can't be derived from the passed domain
definition reliably neither - in some cases (like snapshots or
block copy) the @src is added to the definition only after the
operation succeeded. Therefore, introduce a flag which callers
can use to help us with the decision.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>

src/security/security_dac.c

@@ -889,14 +889,14 @@ static int
 virSecurityDACSetImageLabelInternal(virSecurityManagerPtr mgr,
                                     virDomainDefPtr def,
                                     virStorageSourcePtr src,
-                                    virStorageSourcePtr parent)
+                                    virStorageSourcePtr parent,
+                                    bool isChainTop)
 {
     virSecurityLabelDefPtr secdef;
     virSecurityDeviceLabelDefPtr disk_seclabel;
     virSecurityDeviceLabelDefPtr parent_seclabel = NULL;
     virSecurityDACDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     bool remember;
-    bool is_toplevel = parent == src || parent->externalDataStore == src;
     uid_t user;
     gid_t group;
 
@@ -954,7 +954,7 @@ virSecurityDACSetImageLabelInternal(virSecurityManagerPtr mgr,
      * but the top layer, or read only image, or disk explicitly
      * marked as shared.
      */
-    remember = is_toplevel && !src->readonly && !src->shared;
+    remember = isChainTop && !src->readonly && !src->shared;
 
     return virSecurityDACSetOwnership(mgr, src, NULL, user, group, remember);
 }
@@ -970,7 +970,9 @@ virSecurityDACSetImageLabelRelative(virSecurityManagerPtr mgr,
     virStorageSourcePtr n;
 
     for (n = src; virStorageSourceIsBacking(n); n = n->backingStore) {
-        if (virSecurityDACSetImageLabelInternal(mgr, def, n, parent) < 0)
+        const bool isChainTop = flags & VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP;
+
+        if (virSecurityDACSetImageLabelInternal(mgr, def, n, parent, isChainTop) < 0)
             return -1;
 
         if (n->externalDataStore &&
@@ -983,6 +985,8 @@ virSecurityDACSetImageLabelRelative(virSecurityManagerPtr mgr,
 
         if (!(flags & VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN))
             break;
+
+        flags &= ~VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP;
     }
 
     return 0;
@@ -2114,7 +2118,8 @@ virSecurityDACSetAllLabel(virSecurityManagerPtr mgr,
         if (virDomainDiskGetType(def->disks[i]) == VIR_STORAGE_TYPE_DIR)
             continue;
         if (virSecurityDACSetImageLabel(mgr, def, def->disks[i]->src,
-                                        VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN) < 0)
+                                        VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN |
+                                        VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP) < 0)
             return -1;
     }
 

src/security/security_manager.h

@@ -151,6 +151,10 @@ virSecurityManagerPtr* virSecurityManagerGetNested(virSecurityManagerPtr mgr);
 
 typedef enum {
     VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN = 1 << 0,
+    /* The VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP should be set if the
+     * image passed to virSecurityManagerSetImageLabel() is the top parent of
+     * the whole backing chain. */
+    VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP = 1 << 1,
 } virSecurityDomainImageLabelFlags;
 
 int virSecurityManagerSetImageLabel(virSecurityManagerPtr mgr,

src/security/security_selinux.c

@@ -1824,7 +1824,8 @@ static int
 virSecuritySELinuxSetImageLabelInternal(virSecurityManagerPtr mgr,
                                         virDomainDefPtr def,
                                         virStorageSourcePtr src,
-                                        virStorageSourcePtr parent)
+                                        virStorageSourcePtr parent,
+                                        bool isChainTop)
 {
     virSecuritySELinuxDataPtr data = virSecurityManagerGetPrivateData(mgr);
     virSecurityLabelDefPtr secdef;
@@ -1832,7 +1833,6 @@ virSecuritySELinuxSetImageLabelInternal(virSecurityManagerPtr mgr,
     virSecurityDeviceLabelDefPtr parent_seclabel = NULL;
     char *use_label = NULL;
     bool remember;
-    bool is_toplevel = parent == src || parent->externalDataStore == src;
     g_autofree char *vfioGroupDev = NULL;
     const char *path = src->path;
     int ret;
@@ -1856,7 +1856,7 @@ virSecuritySELinuxSetImageLabelInternal(virSecurityManagerPtr mgr,
      * but the top layer, or read only image, or disk explicitly
      * marked as shared.
      */
-    remember = is_toplevel && !src->readonly && !src->shared;
+    remember = isChainTop && !src->readonly && !src->shared;
 
     disk_seclabel = virStorageSourceGetSecurityLabelDef(src,
                                                         SECURITY_SELINUX_NAME);
@@ -1873,7 +1873,7 @@ virSecuritySELinuxSetImageLabelInternal(virSecurityManagerPtr mgr,
             return 0;
 
         use_label = parent_seclabel->label;
-    } else if (is_toplevel) {
+    } else if (parent == src || parent->externalDataStore == src) {
         if (src->shared) {
             use_label = data->file_context;
         } else if (src->readonly) {
@@ -1930,7 +1930,9 @@ virSecuritySELinuxSetImageLabelRelative(virSecurityManagerPtr mgr,
     virStorageSourcePtr n;
 
     for (n = src; virStorageSourceIsBacking(n); n = n->backingStore) {
-        if (virSecuritySELinuxSetImageLabelInternal(mgr, def, n, parent) < 0)
+        const bool isChainTop = flags & VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP;
+
+        if (virSecuritySELinuxSetImageLabelInternal(mgr, def, n, parent, isChainTop) < 0)
             return -1;
 
         if (n->externalDataStore &&
@@ -1943,6 +1945,8 @@ virSecuritySELinuxSetImageLabelRelative(virSecurityManagerPtr mgr,
 
         if (!(flags & VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN))
             break;
+
+        flags &= ~VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP;
     }
 
     return 0;
@@ -3146,7 +3150,8 @@ virSecuritySELinuxSetAllLabel(virSecurityManagerPtr mgr,
             continue;
         }
         if (virSecuritySELinuxSetImageLabel(mgr, def, def->disks[i]->src,
-                                            VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN) < 0)
+                                            VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN |
+                                            VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP) < 0)
             return -1;
     }
     /* XXX fixme process  def->fss if relabel == true */