security_stack: Perform rollback if one of stacked drivers fails

In order to have multiple security drivers hidden under one
virSecurity* call, we have virSecurityStack driver which holds a
list of registered security drivers and for every virSecurity*
call it iterates over the list and calls corresponding callback
in real security drivers. For instance, for
virSecurityManagerSetAllLabel() it calls
domainSetSecurityAllLabel callback sequentially in NOP, DAC and
(possibly) SELinux or AppArmor drivers. This works just fine if
the callback from every driver returns success. Problem arises
when one of the drivers fails. For instance, aforementioned
SetAllLabel() succeeds for DAC but fails in SELinux in which
case all files that DAC relabelled are now owned by qemu:qemu (or
whomever runs qemu) and thus permissions are leaked. This is even
more visible with XATTRs which remain set for DAC.

The solution is to perform a rollback on failure, i.e. call
opposite action on drivers that succeeded.

I'm providing rollback only for set calls and intentionally
omitting restore calls for two reasons:

1) restore calls are less likely to fail (they merely remove
XATTRs and chown()/setfilecon() file - all of these operations
succeeded in set call),

2) we are not really interested in restore failures - in a very
few places we check for retval of a restore function we do so
only to print a warning.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1740024Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NCole Robinson <crobinso@redhat.com>

src/security/security_stack.c

@@ -24,8 +24,10 @@
 
 #include "virerror.h"
 #include "viralloc.h"
+#include "virlog.h"
 
 #define VIR_FROM_THIS VIR_FROM_SECURITY
+VIR_LOG_INIT("security.security_stack");
 
 typedef struct _virSecurityStackData virSecurityStackData;
 typedef virSecurityStackData *virSecurityStackDataPtr;
@@ -145,14 +147,18 @@ virSecurityStackTransactionStart(virSecurityManagerPtr mgr)
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerTransactionStart(item->securityManager) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev)
+        virSecurityManagerTransactionAbort(item->securityManager);
+    return -1;
 }
 
 
@@ -163,14 +169,18 @@ virSecurityStackTransactionCommit(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerTransactionCommit(item->securityManager, pid, lock) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev)
+        virSecurityManagerTransactionAbort(item->securityManager);
+    return -1;
 }
 
 
@@ -278,17 +288,31 @@ virSecurityStackSetHostdevLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetHostdevLabel(item->securityManager,
                                               vm,
                                               dev,
                                               vroot) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerRestoreHostdevLabel(item->securityManager,
+                                                  vm,
+                                                  dev,
+                                                  vroot) < 0) {
+            VIR_WARN("Unable to restore hostdev label after failed set label "
+                     "call virDriver=%s driver=%s domain=%s hostdev=%p",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     vm->name, dev);
+        }
+    }
+    return -1;
 }
 
 
@@ -323,16 +347,30 @@ virSecurityStackSetAllLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetAllLabel(item->securityManager, vm,
                                           stdin_path, chardevStdioLogd,
                                           migrated) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerRestoreAllLabel(item->securityManager,
+                                              vm,
+                                              migrated,
+                                              chardevStdioLogd) < 0) {
+            VIR_WARN("Unable to restore all labels after failed set label call "
+                     "virDriver=%s driver=%s domain=%s migrated=%d",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     vm->name, migrated);
+        }
+    }
+    return -1;
 }
 
 
@@ -363,14 +401,27 @@ virSecurityStackSetSavedStateLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetSavedStateLabel(item->securityManager, vm, savefile) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerRestoreSavedStateLabel(item->securityManager,
+                                                     vm,
+                                                     savefile) < 0) {
+            VIR_WARN("Unable to restore saved state label after failed set "
+                     "label call virDriver=%s driver=%s savefile=%s",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     savefile);
+        }
+    }
+    return -1;
 }
 
 
@@ -451,14 +502,25 @@ virSecurityStackSetDaemonSocketLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetDaemonSocketLabel(item->securityManager, vm) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerClearSocketLabel(item->securityManager,
+                                               vm) < 0) {
+            VIR_WARN("Unable to clear new daemon socket label after failed "
+                     "set label call virDriver=%s driver=%s domain=%s",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     vm->name);
+        }
+    }
+    return -1;
 }
 
 
@@ -468,14 +530,25 @@ virSecurityStackSetSocketLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetSocketLabel(item->securityManager, vm) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerClearSocketLabel(item->securityManager,
+                                               vm) < 0) {
+            VIR_WARN("Unable to clear new socket label after failed "
+                     "set label call virDriver=%s driver=%s domain=%s",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     vm->name);
+        }
+    }
+    return -1;
 }
 
 
@@ -573,15 +646,30 @@ virSecurityStackSetImageLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetImageLabel(item->securityManager, vm, src,
                                             flags) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerRestoreImageLabel(item->securityManager,
+                                                vm,
+                                                src,
+                                                flags) < 0) {
+            VIR_WARN("Unable to restore image label after failed set label "
+                     "call virDriver=%s driver=%s domain=%s src=%p (path=%s) "
+                     "flags=0x%x",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     vm->name, src, NULLSTR(src->path), flags);
+        }
+    }
+    return -1;
 }
 
 static int
@@ -629,14 +717,27 @@ virSecurityStackSetMemoryLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetMemoryLabel(item->securityManager, vm, mem) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerRestoreMemoryLabel(item->securityManager,
+                                                 vm,
+                                                 mem) < 0) {
+            VIR_WARN("Unable to restore memory label after failed set label "
+                     "call virDriver=%s driver=%s domain=%s mem=%p",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     vm->name, mem);
+        }
+    }
+    return -1;
 }
 
 static int
@@ -664,14 +765,27 @@ virSecurityStackSetInputLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetInputLabel(item->securityManager, vm, input) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerRestoreInputLabel(item->securityManager,
+                                                vm,
+                                                input) < 0) {
+            VIR_WARN("Unable to restore input label after failed set label "
+                     "call virDriver=%s driver=%s domain=%s input=%p",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     vm->name, input);
+        }
+    }
+    return -1;
 }
 
 static int
@@ -719,16 +833,30 @@ virSecurityStackDomainSetChardevLabel(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetChardevLabel(item->securityManager,
                                               def, dev_source,
                                               chardevStdioLogd) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerRestoreChardevLabel(item->securityManager,
+                                                  def,
+                                                  dev_source,
+                                                  chardevStdioLogd) < 0) {
+            VIR_WARN("Unable to restore chardev label after failed set label "
+                     "call virDriver=%s driver=%s domain=%s dev_source=%p",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     def->name, dev_source);
+        }
+    }
+    return -1;
 }
 
 static int
@@ -758,15 +886,27 @@ virSecurityStackSetTPMLabels(virSecurityManagerPtr mgr,
 {
     virSecurityStackDataPtr priv = virSecurityManagerGetPrivateData(mgr);
     virSecurityStackItemPtr item = priv->itemsHead;
-    int rc = 0;
 
     for (; item; item = item->next) {
         if (virSecurityManagerSetTPMLabels(item->securityManager,
                                            vm) < 0)
-            rc = -1;
+            goto rollback;
     }
 
-    return rc;
+    return 0;
+
+ rollback:
+    for (item = item->prev; item; item = item->prev) {
+        if (virSecurityManagerRestoreTPMLabels(item->securityManager,
+                                               vm) < 0) {
+            VIR_WARN("Unable to restore TPM label after failed set label "
+                     "call virDriver=%s driver=%s domain=%s",
+                     virSecurityManagerGetVirtDriver(mgr),
+                     virSecurityManagerGetDriver(item->securityManager),
+                     vm->name);
+        }
+    }
+    return -1;
 }