[NTOS:OB] Clarify and fix the usage of the Obp*DirectoryLock*() and ObpReleaseLookupContextObject() functions.

- Disentangle the usage of ObpAcquireDirectoryLockExclusive() when it's
  used only for accessing a directory structure, or as part of a lookup
  operation.

  The Obp*DirectoryLock*() -- both shared and exclusive -- functions
  are only for locking an OB directory, for reading or writing its
  structure members.

  When performing lookup operations (insertions/deletions of entries
  within a directory), use a ObpAcquireLookupContextLock() function that
  exclusively locks the directory and saves extra lock state, that can
  be used by ObpReleaseLookupContextObject() for cleanup.

- Add documentation for these functions.

ntoskrnl/include/internal/ob_x.h

@@ -169,15 +169,26 @@ ObpDereferenceNameInfo(IN POBJECT_HEADER_NAME_INFO HeaderNameInfo)
     }
 }
 
+/**
+ * @brief
+ * Locks a directory for shared access.
+ * Used for reading members of the directory object.
+ *
+ * @param[in] Directory
+ * The directory to lock.
+ *
+ * @param[in] Context
+ * The lookup lock context.
+ */
 FORCEINLINE
 VOID
 ObpAcquireDirectoryLockShared(IN POBJECT_DIRECTORY Directory,
                               IN POBP_LOOKUP_CONTEXT Context)
 {
-    /* It's not, set lock flag */
+    /* Update lock flag */
     Context->LockStateSignature = OBP_LOCK_STATE_PRE_ACQUISITION_SHARED;
 
-    /* Lock it */
+    /* Acquire an shared directory lock */
     KeEnterCriticalRegion();
     ExAcquirePushLockShared(&Directory->Lock);
 
@@ -185,6 +196,17 @@ ObpAcquireDirectoryLockShared(IN POBJECT_DIRECTORY Directory,
     Context->LockStateSignature = OBP_LOCK_STATE_POST_ACQUISITION_SHARED;
 }
 
+/**
+ * @brief
+ * Locks a directory for exclusive access.
+ * Used for writing/reading members of the directory object.
+ *
+ * @param[in] Directory
+ * The directory to lock.
+ *
+ * @param[in] Context
+ * The lookup lock context.
+ */
 FORCEINLINE
 VOID
 ObpAcquireDirectoryLockExclusive(IN POBJECT_DIRECTORY Directory,
@@ -197,14 +219,20 @@ ObpAcquireDirectoryLockExclusive(IN POBJECT_DIRECTORY Directory,
     KeEnterCriticalRegion();
     ExAcquirePushLockExclusive(&Directory->Lock);
 
-    /* Set the directory */
+    /* Update lock flag */
-    Context->Directory = Directory;
-
-    /* Update lock settings */
     Context->LockStateSignature = OBP_LOCK_STATE_POST_ACQUISITION_EXCLUSIVE;
-    Context->DirectoryLocked = TRUE;
 }
 
+/**
+ * @brief
+ * Unlocks a previously shared or exclusively locked directory.
+ *
+ * @param[in] Directory
+ * The directory to unlock.
+ *
+ * @param[in] Context
+ * The lookup lock context.
+ */
 FORCEINLINE
 VOID
 ObpReleaseDirectoryLock(IN POBJECT_DIRECTORY Directory,
@@ -216,6 +244,15 @@ ObpReleaseDirectoryLock(IN POBJECT_DIRECTORY Directory,
     KeLeaveCriticalRegion();
 }
 
+/**
+ * @brief
+ * Initializes a new object directory lookup context.
+ * Used for lookup operations (insertions/deletions) in a directory.
+ * Employed in conjunction with the directory locking functions.
+ *
+ * @param[in] Context
+ * The new lookup context to initialize.
+ */
 FORCEINLINE
 VOID
 ObpInitializeLookupContext(IN POBP_LOOKUP_CONTEXT Context)
@@ -227,6 +264,29 @@ ObpInitializeLookupContext(IN POBP_LOOKUP_CONTEXT Context)
     Context->LockStateSignature = OBP_LOCK_STATE_INITIALIZED;
 }
 
+/**
+ * @brief
+ * Locks an object directory lookup context for performing
+ * lookup operations (insertions/deletions) in a directory.
+ * The directory is locked for exclusive access.
+ *
+ * @param[in] Context
+ * The lookup context to lock.
+ *
+ * @param[in] Directory
+ * The directory on which the lookup context applies.
+ */
+FORCEINLINE
+VOID
+ObpAcquireLookupContextLock(IN POBP_LOOKUP_CONTEXT Context,
+                            IN POBJECT_DIRECTORY Directory)
+{
+    /* Acquire an exclusive directory lock and save its lock state */
+    ObpAcquireDirectoryLockExclusive(Directory, Context);
+    Context->Directory = Directory;
+    Context->DirectoryLocked = TRUE;
+}
+
 FORCEINLINE
 VOID
 ObpReleaseLookupContextObject(IN POBP_LOOKUP_CONTEXT Context)
@@ -234,14 +294,14 @@ ObpReleaseLookupContextObject(IN POBP_LOOKUP_CONTEXT Context)
     POBJECT_HEADER ObjectHeader;
     POBJECT_HEADER_NAME_INFO HeaderNameInfo;
 
-    /* Check if we had found an object */
+    /* Check if we had an object */
     if (Context->Object)
     {
         /* Get the object name information */
         ObjectHeader = OBJECT_TO_OBJECT_HEADER(Context->Object);
         HeaderNameInfo = OBJECT_HEADER_TO_NAME_INFO(ObjectHeader);
 
-        /* release the name information */
+        /* Release the name information */
         ObpDereferenceNameInfo(HeaderNameInfo);
 
         /* Dereference the object */
@@ -250,6 +310,14 @@ ObpReleaseLookupContextObject(IN POBP_LOOKUP_CONTEXT Context)
     }
 }
 
+/**
+ * @brief
+ * Releases an initialized object directory lookup context.
+ * Unlocks it if necessary, and dereferences the underlying object.
+ *
+ * @param[in] Context
+ * The lookup context to release.
+ */
 FORCEINLINE
 VOID
 ObpReleaseLookupContext(IN POBP_LOOKUP_CONTEXT Context)
@@ -257,7 +325,7 @@ ObpReleaseLookupContext(IN POBP_LOOKUP_CONTEXT Context)
     /* Check if we came back with the directory locked */
     if (Context->DirectoryLocked)
     {
-        /* Release the lock */
+        /* Release the directory lock */
         ObpReleaseDirectoryLock(Context->Directory, Context);
         Context->Directory = NULL;
         Context->DirectoryLocked = FALSE;

ntoskrnl/ob/obdir.c

@@ -573,7 +573,7 @@ NtQueryDirectoryObject(IN HANDLE DirectoryHandle,
         return Status;
     }
 
-    /* Lock directory in shared mode */
+    /* Lock the directory in shared mode */
     ObpAcquireDirectoryLockShared(Directory, &LookupContext);
 
     /* Start at position 0 */

ntoskrnl/ob/obinit.c

@@ -386,11 +386,9 @@ ObPostPhase0:
     Status = NtClose(Handle);
     if (!NT_SUCCESS(Status)) return FALSE;
 
-    /* Initialize lookup context */
+    /* Initialize the lookup context and lock it */
     ObpInitializeLookupContext(&Context);
-
+    ObpAcquireLookupContextLock(&Context, ObpTypeDirectoryObject);
-    /* Lock it */
-    ObpAcquireDirectoryLockExclusive(ObpTypeDirectoryObject, &Context);
 
     /* Loop the object types */
     ListHead = &ObpTypeObjectType->TypeList;

ntoskrnl/ob/oblife.c

@@ -1093,8 +1093,8 @@ ObCreateObjectType(IN PUNICODE_STRING TypeName,
     /* Check if we've already created the directory of types */
     if (ObpTypeDirectoryObject)
     {
-        /* Acquire the directory lock */
+        /* Lock the lookup context */
-        ObpAcquireDirectoryLockExclusive(ObpTypeDirectoryObject, &Context);
+        ObpAcquireLookupContextLock(&Context, ObpTypeDirectoryObject);
 
         /* Do the lookup */
         if (ObpLookupEntryDirectory(ObpTypeDirectoryObject,
@@ -1853,7 +1853,7 @@ NtSetInformationObject(IN HANDLE ObjectHandle,
                     OBP_LOOKUP_CONTEXT LookupContext;
                     ObpInitializeLookupContext(&LookupContext);
 
-                    /* Set its session ID */
+                    /* Set the directory session ID */
                     ObpAcquireDirectoryLockExclusive(Directory, &LookupContext);
                     Directory->SessionId = PsGetCurrentProcessSessionId();
                     ObpReleaseDirectoryLock(Directory, &LookupContext);

ntoskrnl/ob/obname.c

@@ -321,11 +321,9 @@ ObpDeleteNameCheck(IN PVOID Object)
          (ObjectNameInfo->Directory) &&
          !(ObjectHeader->Flags & OB_FLAG_PERMANENT))
     {
-        /* Setup a lookup context */
+        /* Setup a lookup context and lock it */
         ObpInitializeLookupContext(&Context);
-
+        ObpAcquireLookupContextLock(&Context, ObjectNameInfo->Directory);
-        /* Lock the directory */
-        ObpAcquireDirectoryLockExclusive(ObjectNameInfo->Directory, &Context);
 
         /* Do the lookup */
         Object = ObpLookupEntryDirectory(ObjectNameInfo->Directory,
@@ -352,7 +350,7 @@ ObpDeleteNameCheck(IN PVOID Object)
                     ObpDeleteSymbolicLinkName(Object);
                 }
 
-                /* Check if the kernel exclusive is set */
+                /* Check if the kernel exclusive flag is set */
                 ObjectNameInfo = OBJECT_HEADER_TO_NAME_INFO(ObjectHeader);
                 if ((ObjectNameInfo) &&
                     (ObjectNameInfo->QueryReferences & OB_FLAG_KERNEL_EXCLUSIVE))
@@ -843,8 +841,8 @@ ParseFromRoot:
                 /* Check if we are inserting an object */
                 if (InsertObject)
                 {
-                    /* Lock the directory */
+                    /* Lock the lookup context */
-                    ObpAcquireDirectoryLockExclusive(Directory, LookupContext);
+                    ObpAcquireLookupContextLock(LookupContext, Directory);
                 }
             }