qemu_conf: Check for namespaces availability more wisely

The bare fact that mnt namespace is available is not enough for
us to allow/enable qemu namespaces feature. There are other
requirements: we must copy all the ACL & SELinux labels otherwise
we might grant access that is administratively forbidden or vice
versa.
At the same time, the check for namespace prerequisites is moved
from domain startup time to qemu.conf parser as it doesn't make
much sense to allow users to start misconfigured libvirt just to
find out they can't start a single domain.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_conf.c

@@ -321,12 +321,10 @@ virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged)
     if (!(cfg->namespaces = virBitmapNew(QEMU_DOMAIN_NS_LAST)))
         goto error;
 
-#if defined(__linux__)
     if (privileged &&
-        virProcessNamespaceAvailable(VIR_PROCESS_NAMESPACE_MNT) == 0 &&
+        qemuDomainNamespaceAvailable(QEMU_DOMAIN_NS_MOUNT) &&
         virBitmapSetBit(cfg->namespaces, QEMU_DOMAIN_NS_MOUNT) < 0)
         goto error;
-#endif /* defined(__linux__) */
 
 #ifdef DEFAULT_LOADER_NVRAM
     if (virFirmwareParseList(DEFAULT_LOADER_NVRAM,
@@ -438,7 +436,8 @@ virQEMUDriverConfigHugeTLBFSInit(virHugeTLBFSPtr hugetlbfs,
 
 
 int virQEMUDriverConfigLoadFile(virQEMUDriverConfigPtr cfg,
-                                const char *filename)
+                                const char *filename,
+                                bool privileged)
 {
     virConfPtr conf = NULL;
     int ret = -1;
@@ -832,6 +831,19 @@ int virQEMUDriverConfigLoadFile(virQEMUDriverConfigPtr cfg,
                 goto cleanup;
             }
 
+            if (!privileged) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("cannot use namespaces in session mode"));
+                goto cleanup;
+            }
+
+            if (qemuDomainNamespaceAvailable(ns) < 0) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                               _("%s namespace is not available"),
+                               namespaces[i]);
+                goto cleanup;
+            }
+
             if (virBitmapSetBit(cfg->namespaces, ns) < 0) {
                 virReportError(VIR_ERR_INTERNAL_ERROR,
                                _("Unable to enable namespace: %s"),

src/qemu/qemu_conf.h

@@ -294,7 +294,8 @@ void qemuDomainCmdlineDefFree(qemuDomainCmdlineDefPtr def);
 virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged);
 
 int virQEMUDriverConfigLoadFile(virQEMUDriverConfigPtr cfg,
-                                const char *filename);
+                                const char *filename,
+                                bool privileged);
 
 virQEMUDriverConfigPtr virQEMUDriverGetConfig(virQEMUDriverPtr driver);
 bool virQEMUDriverIsPrivileged(virQEMUDriverPtr driver);

src/qemu/qemu_domain.c

@@ -7643,21 +7643,8 @@ qemuDomainCreateNamespace(virQEMUDriverPtr driver,
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     int ret = -1;
 
-    if (!virBitmapIsBitSet(cfg->namespaces, QEMU_DOMAIN_NS_MOUNT)) {
-        ret = 0;
-        goto cleanup;
-    }
-
-    if (!virQEMUDriverIsPrivileged(driver)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("cannot use namespaces in session mode"));
-        goto cleanup;
-    }
-
-    if (virProcessNamespaceAvailable(VIR_PROCESS_NAMESPACE_MNT) < 0)
-        goto cleanup;
-
-    if (qemuDomainEnableNamespace(vm, QEMU_DOMAIN_NS_MOUNT) < 0)
+    if (virBitmapIsBitSet(cfg->namespaces, QEMU_DOMAIN_NS_MOUNT) &&
+        qemuDomainEnableNamespace(vm, QEMU_DOMAIN_NS_MOUNT) < 0)
         goto cleanup;
 
     ret = 0;
@@ -7667,6 +7654,35 @@ qemuDomainCreateNamespace(virQEMUDriverPtr driver,
 }
 
 
+bool
+qemuDomainNamespaceAvailable(qemuDomainNamespace ns ATTRIBUTE_UNUSED)
+{
+#if !defined(__linux__)
+    /* Namespaces are Linux specific. */
+    return false;
+
+#else /* defined(__linux__) */
+
+    switch (ns) {
+    case QEMU_DOMAIN_NS_MOUNT:
+# if !defined(HAVE_SYS_ACL_H) || !defined(WITH_SELINUX)
+        /* We can't create the exact copy of paths if either of
+         * these is not available. */
+        return false;
+# else
+        if (virProcessNamespaceAvailable(VIR_PROCESS_NAMESPACE_MNT) < 0)
+            return false;
+# endif
+        break;
+    case QEMU_DOMAIN_NS_LAST:
+        break;
+    }
+
+    return true;
+#endif /* defined(__linux__) */
+}
+
+
 struct qemuDomainAttachDeviceMknodData {
     virQEMUDriverPtr driver;
     virDomainObjPtr vm;

src/qemu/qemu_domain.h

@@ -808,6 +808,8 @@ int qemuDomainBuildNamespace(virQEMUDriverPtr driver,
 int qemuDomainCreateNamespace(virQEMUDriverPtr driver,
                               virDomainObjPtr vm);
 
+bool qemuDomainNamespaceAvailable(qemuDomainNamespace ns);
+
 int qemuDomainNamespaceSetupDisk(virQEMUDriverPtr driver,
                                  virDomainObjPtr vm,
                                  virStorageSourcePtr src);

src/qemu/qemu_driver.c

@@ -676,7 +676,7 @@ qemuStateInitialize(bool privileged,
     if (virAsprintf(&driverConf, "%s/qemu.conf", cfg->configBaseDir) < 0)
         goto error;
 
-    if (virQEMUDriverConfigLoadFile(cfg, driverConf) < 0)
+    if (virQEMUDriverConfigLoadFile(cfg, driverConf, privileged) < 0)
         goto error;
     VIR_FREE(driverConf);