[libvirt] add security hook for permitting hugetlbfs access (v2)

[Serge Hallyn]

When a qemu domain is backed by huge pages, apparmor needs to grant the domain
rw access to files under the hugetlbfs mount point.  Add a hook, called in
qemu_process.c, which ends up adding the read-write access through
virt-aa-helper.  Qemu will be creating a randomly named file under the
mountpoint and unlinking it as soon as it has mmap()d it, therefore we
cannot predict the full pathname, but for the same reason it is generally
safe to provide access to $path/**.

Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/646468

Changelog: (v2) use virBuffer in place of snprintf.

Index: libvirt/src/qemu/qemu_process.c
===================================================================
--- libvirt.orig/src/qemu/qemu_process.c	2012-12-06 11:50:48.354763986 -0600
+++ libvirt/src/qemu/qemu_process.c	2012-12-06 11:57:58.234773649 -0600
@@ -3475,6 +3475,15 @@
     }
     virDomainAuditSecurityLabel(vm, true);
 
+    if (driver->hugepage_path && vm->def->mem.hugepage_backed) {
+        if (virSecurityManagerSetHugepages(driver->securityManager,
+                    vm->def, driver->hugepage_path) < 0) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                    "%s", _("Unable to set huge path in security driver"));
+            goto cleanup;
+        }
+    }
+
     /* Ensure no historical cgroup for this VM is lying around bogus
      * settings */
     VIR_DEBUG("Ensuring no historical cgroup is lying around");
Index: libvirt/src/security/security_apparmor.c
===================================================================
--- libvirt.orig/src/security/security_apparmor.c	2012-12-06 11:50:48.354763986 -0600
+++ libvirt/src/security/security_apparmor.c	2012-12-06 11:58:23.286774213 -0600
@@ -840,6 +840,31 @@
 }
 
 static int
+ApparmorSetHugepages(virSecurityManagerPtr mgr,
+                        virDomainDefPtr def,
+                        const char *path)
+{
+    const virSecurityLabelDefPtr secdef =
+        virDomainDefGetSecurityLabelDef(def, SECURITY_APPARMOR_NAME);
+    int ret = -1;
+    virBuffer buf = VIR_BUFFER_INITIALIZER;
+    char *newpath;
+
+    if (!secdef)
+        return -1;
+
+    if (secdef->imagelabel == NULL)
+        return 0;
+
+    virBufferAsprintf(&buf, "%s/**", path);
+    newpath = virBufferCurrentContent(&buf);
+    if (newpath)
+        ret = reload_profile(mgr, def, newpath, true);
+    virBufferFreeAndReset(&buf);
+    return ret;
+}
+
+static int
 AppArmorSetFDLabel(virSecurityManagerPtr mgr,
                         virDomainDefPtr def,
                         int fd)
@@ -908,4 +933,6 @@
 
     .domainSetSecurityImageFDLabel      = AppArmorSetFDLabel,
     .domainSetSecurityTapFDLabel        = AppArmorSetFDLabel,
+
+    .domainSetSecurityHugepages         = ApparmorSetHugepages,
 };
Index: libvirt/src/security/security_manager.c
===================================================================
--- libvirt.orig/src/security/security_manager.c	2012-12-06 11:50:48.354763986 -0600
+++ libvirt/src/security/security_manager.c	2012-12-06 11:57:58.238773649 -0600
@@ -511,3 +511,13 @@
     list[1] = NULL;
     return list;
 }
+
+int virSecurityManagerSetHugepages(virSecurityManagerPtr mgr,
+                                    virDomainDefPtr vm,
+                                    const char *path)
+{
+    if (mgr->drv->domainSetSecurityHugepages)
+        return mgr->drv->domainSetSecurityHugepages(mgr, vm, path);
+
+    return 0;
+}
Index: libvirt/src/security/security_manager.h
===================================================================
--- libvirt.orig/src/security/security_manager.h	2012-12-06 11:50:48.354763986 -0600
+++ libvirt/src/security/security_manager.h	2012-12-06 11:57:58.238773649 -0600
@@ -112,5 +112,8 @@
                                               virDomainDefPtr vm);
 virSecurityManagerPtr*
 virSecurityManagerGetNested(virSecurityManagerPtr mgr);
+int virSecurityManagerSetHugepages(virSecurityManagerPtr mgr,
+                                  virDomainDefPtr sec,
+                                  const char *hugepages_path);
 
 #endif /* VIR_SECURITY_MANAGER_H__ */
Index: libvirt/src/security/security_driver.h
===================================================================
--- libvirt.orig/src/security/security_driver.h	2012-12-06 11:50:48.354763986 -0600
+++ libvirt/src/security/security_driver.h	2012-12-06 11:57:58.238773649 -0600
@@ -100,6 +100,9 @@
                                                int fd);
 typedef char *(*virSecurityDomainGetMountOptions) (virSecurityManagerPtr mgr,
                                                          virDomainDefPtr def);
+typedef int (*virSecurityDomainSetHugepages) (virSecurityManagerPtr mgr,
+                                                         virDomainDefPtr def,
+                                                         const char *path);
 
 struct _virSecurityDriver {
     size_t privateDataLen;
@@ -140,6 +143,7 @@
     virSecurityDomainSetTapFDLabel domainSetSecurityTapFDLabel;
 
     virSecurityDomainGetMountOptions domainGetSecurityMountOptions;
+    virSecurityDomainSetHugepages domainSetSecurityHugepages;
 };
 
 virSecurityDriverPtr virSecurityDriverLookup(const char *name,
Index: libvirt/src/libvirt_private.syms
===================================================================
--- libvirt.orig/src/libvirt_private.syms	2012-12-06 11:50:48.354763986 -0600
+++ libvirt/src/libvirt_private.syms	2012-12-06 11:57:58.238773649 -0600
@@ -1052,6 +1052,7 @@
 virSecurityManagerStackAddNested;
 virSecurityManagerVerify;
 virSecurityManagerGetMountOptions;
+virSecurityManagerSetHugepages;
 
 # sexpr.h
 sexpr_append;
Index: libvirt/src/security/security_stack.c
===================================================================
--- libvirt.orig/src/security/security_stack.c	2012-12-06 11:50:48.354763986 -0600
+++ libvirt/src/security/security_stack.c	2012-12-06 11:57:58.238773649 -0600
@@ -462,6 +462,23 @@
     return rc;
 }
 
+static int
+virSecurityStackSetHugepages(virSecurityManagerPtr mgr,
+                              virDomainDefPtr vm,
+                              const char *path)
+{
+    virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
+    virSecurityStackItemPtr item = priv->itemsHead;
+    int rc = 0;
+
+    for (; item; item = item->next) {
+        if (virSecurityManagerSetHugepages(item->securityManager, vm, path) < 0)
+            rc = -1;
+    }
+
+    return rc;
+}
+
 static char *virSecurityStackGetMountOptions(virSecurityManagerPtr mgr ATTRIBUTE_UNUSED,
                                              virDomainDefPtr vm ATTRIBUTE_UNUSED) {
     return NULL;
@@ -529,4 +546,6 @@
     .domainSetSecurityTapFDLabel        = virSecurityStackSetTapFDLabel,
 
     .domainGetSecurityMountOptions      = virSecurityStackGetMountOptions,
+
+    .domainSetSecurityHugepages         = virSecurityStackSetHugepages,
 };