Fix possible recursion bug. (#30)

Resolving ATTRIBUTE_LIST recursively could get into a recursive loop.

Fixes: #29

parser/attribute.go

@@ -681,16 +681,18 @@ func (self *ATTRIBUTE_LIST_ENTRY) Attributes(
 		attr_list_entry := self.Profile.ATTRIBUTE_LIST_ENTRY(
 			self.Reader, self.Offset+offset)
 
-		Printf("ATTRIBUTE_LIST_ENTRY %v\n",
-			attr_list_entry.DebugString())
+		Printf("%v ATTRIBUTE_LIST_ENTRY %v\n", mft_entry.Record_number(),
+			DebugString(attr_list_entry, ""))
 
 		// The attribute_list_entry points to a different MFT
 		// entry than the one we are working on now. We need
 		// to fetch it from there.
+		mft_ref := attr_list_entry.MftReference()
 		if ntfs.RootMFT != nil &&
-			attr_list_entry.MftReference() != uint64(mft_entry.Record_number()) {
+			mft_ref != uint64(mft_entry.Record_number()) {
 
-			Printf("Fetching from MFT Entry %v\n", attr_list_entry.MftReference())
+			Printf("While working on %v - Fetching from MFT Entry %v\n",
+				mft_entry.Record_number(), mft_ref)
 			attr, err := attr_list_entry.GetAttribute(ntfs)
 			if err != nil {
 				Printf("Error %v\n", err)
@@ -723,14 +725,13 @@ func (self *ATTRIBUTE_LIST_ENTRY) GetAttribute(
 	if err != nil {
 		return nil, err
 	}
-	for _, attr := range mft.EnumerateAttributes(ntfs) {
-		if attr.Type().Value == uint64(mytype) &&
-			attr.Attribute_id() == uint16(myid) {
-			return attr, nil
-		}
+	res, err := mft.GetDirectAttribute(ntfs, mytype, uint16(myid))
+	if err != nil {
+		Printf("MFT %v not found in target\n", mft.Record_number())
+	} else {
+		Printf("Found %v\n", DebugString(res, "  "))
 	}
-
-	return nil, errors.New("No attribute found.")
+	return res, err
 }
 
 // The STANDARD_INDEX_HEADER has a second layer of fixups.

parser/debug.go

@@ -25,7 +25,7 @@ type Debugger interface {
 
 func DebugString(arg interface{}, indent string) string {
 	debugger, ok := arg.(Debugger)
-	if ok {
+	if debug && ok {
 		lines := strings.Split(debugger.DebugString(), "\n")
 		for idx, line := range lines {
 			lines[idx] = indent + line

parser/mft.go

@@ -50,6 +50,53 @@ func (self *MFT_ENTRY) EnumerateAttributes(ntfs *NTFSContext) []*NTFS_ATTRIBUTE
 	return result
 }
 
+// See https://github.com/CCXLabs/CCXDigger/issues/13
+
+// It is possible that an attribute list is pointing to an mft entry
+// which also contains an attribute list. The second attribute list
+// may also point to another entry inside the first MFT entry. This
+// causes an infinite loop.
+
+// Previous versions of the code erroneously called
+// EnumerateAttributes to resolve a foreign attribute reference but
+// this is not strictly correct because a foreign reference is never
+// indirect and so never should traverse ATTRIBUTE_LISTs recursively
+// anyway.
+
+// The GetDirectAttribute() function looks for an exact attribute and
+// type inside an MFT entry without following any attribute
+// lists. This breaks the recursion and is a more correct approach.
+
+// Search the MFT entry for a contained attribute - does not expand
+// ATTRIBUTE_LISTs. This version is suitable to be called from within
+// an ATTRIBUTE_LIST expansion.
+func (self *MFT_ENTRY) GetDirectAttribute(
+	ntfs *NTFSContext, attr_type uint64, attr_id uint16) (*NTFS_ATTRIBUTE, error) {
+	offset := int64(self.Attribute_offset())
+
+	for {
+		// Instantiate the attribute over the fixed up address space.
+		attribute := self.Profile.NTFS_ATTRIBUTE(self.Reader, offset)
+
+		// Reached the end of the MFT entry.
+		mft_size := int64(self.Mft_entry_size())
+		attribute_size := int64(attribute.Length())
+		if attribute_size == 0 ||
+			attribute_size+offset > mft_size {
+			break
+		}
+
+		if attribute.Type().Value == attr_type &&
+			attribute.Attribute_id() == attr_id {
+			return attribute, nil
+		}
+
+		// Go to the next attribute.
+		offset += int64(attribute.Length())
+	}
+	return nil, errors.New("No attribute found.")
+}
+
 // Open the MFT entry specified by a path name. Walks all directory
 // indexes in the path to find the right MFT entry.
 func (self *MFT_ENTRY) Open(ntfs *NTFSContext, filename string) (*MFT_ENTRY, error) {