Fix buggy font (#283)

* Adds checksum on font file reading

* fix name table parsing on broken table

* only warn if checksum invalid, avoid exception with bounds check #258

also returns a null object when the object generation number exceeds
ushort.maxvalue since this is the maximum allowed value and this
broke tests attempting to parse all objects in the file from #258

* remove potentially problematic document

it might be sensitive data

* use ttf from file to test without including full file

Co-authored-by: romain v <rvergnory@lucca.fr>

src/UglyToad.PdfPig.Fonts/TrueType/Parser/NameTableParser.cs

@@ -22,10 +22,19 @@
             }
 
             var strings = new TrueTypeNameRecord[count];
+            var offset = header.Offset + stringOffset;
             for (var i = 0; i < count; i++)
             {
-                var nameRecord = names[i];
+                strings[i] = GetTrueTypeNameRecord(names[i], data, offset);
+            }
 
+            return new NameTable(header, GetName(4, strings), GetName(1, strings), GetName(2, strings), strings);
+        }
+
+        private static TrueTypeNameRecord GetTrueTypeNameRecord(NameRecordBuilder nameRecord, TrueTypeDataBytes data, uint offset)
+        {
+            try
+            {
                 var encoding = OtherEncodings.Iso88591;
 
                 switch (nameRecord.PlatformId)
@@ -62,16 +71,23 @@
                         }
                 }
 
-                var position = header.Offset + stringOffset + nameRecord.Offset;
+                var position = offset + nameRecord.Offset;
+
+                if (position >= data.Length)
+                {
+                    return null;
+                }
 
                 data.Seek(position);
 
                 var str = data.ReadString(nameRecord.Length, encoding);
 
-                strings[i] = nameRecord.ToNameRecord(str);
+                return nameRecord.ToNameRecord(str);
+            }
+            catch
+            {
+                return null;
             }
-
-            return new NameTable(header, GetName(4, strings), GetName(1, strings), GetName(2, strings), strings);
         }
 
         private static string GetName(int nameId, TrueTypeNameRecord[] names)
@@ -84,7 +100,7 @@
             {
                 var name = names[i];
 
-                if (name.NameId != nameId)
+                if (name is null || name.NameId != nameId)
                 {
                     continue;
                 }

src/UglyToad.PdfPig.Fonts/TrueType/Parser/TableParser.cs

@@ -1,6 +1,7 @@
 namespace UglyToad.PdfPig.Fonts.TrueType.Parser
 {
     using System;
+    using System.Diagnostics;
     using Tables;
 
     internal static class TableParser
@@ -13,6 +14,20 @@
 
         public static T Parse<T>(TrueTypeHeaderTable table, TrueTypeDataBytes data, TableRegister.Builder register) where T : ITrueTypeTable
         {
+            //checksum https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6.html
+            uint sum = 0;
+            var nLongs = (table.Length + 3) / 4;
+            data.Seek(table.Offset);
+            while (nLongs-- > 0)
+            {
+                sum += (uint)data.ReadSignedInt();
+            }
+
+            if (sum != table.CheckSum)
+            {
+                Trace.TraceWarning("Table with invalid checksum found in TrueType font file.");
+            }
+
             if (typeof(T) == typeof(CMapTable))
             {
                 return (T) (object) CMapTableParser.Parse(table, data, register);

src/UglyToad.PdfPig.Fonts/TrueType/Tables/NameTable.cs

@@ -61,7 +61,7 @@
             string any = null;
             foreach (var nameRecord in NameRecords)
             {
-                if (nameRecord.NameId != 6)
+                if (nameRecord is null || nameRecord.NameId != 6)
                 {
                     continue;
                 }

src/UglyToad.PdfPig.Tests/Fonts/TrueType/Parser/TrueTypeFontParserTests.cs

@@ -210,6 +210,20 @@ namespace UglyToad.PdfPig.Tests.Fonts.TrueType.Parser
                 Assert.Equal(points, glyph.Points.Length);
             }
         }
+
+        [Fact]
+        public void ParseIssue258CorruptNameTable()
+        {
+            var bytes = TrueTypeTestHelper.GetFileBytes("issue-258-corrupt-name-table");
+
+            var input = new TrueTypeDataBytes(new ByteArrayInputBytes(bytes));
+
+            var font = TrueTypeFontParser.Parse(input);
+
+            Assert.NotNull(font);
+            Assert.NotNull(font.TableRegister.NameTable);
+            Assert.NotEmpty(font.TableRegister.NameTable.NameRecords);
+        }
     }
 }
 

src/UglyToad.PdfPig.Tests/UglyToad.PdfPig.Tests.csproj

@@ -39,6 +39,7 @@
   <ItemGroup>
     <EmbeddedResource Remove="Fonts\TrueType\Andada-Regular.ttf" />
     <EmbeddedResource Remove="Fonts\TrueType\google-simple-doc.ttf" />
+    <EmbeddedResource Remove="Fonts\TrueType\issue-258-corrupt-name-table.ttf" />
     <EmbeddedResource Remove="Fonts\TrueType\PMingLiU.ttf" />
     <EmbeddedResource Remove="Fonts\TrueType\Roboto-Regular.ttf" />
     <EmbeddedResource Remove="Fonts\Type1\AdobeUtopia.pfa" />
@@ -64,6 +65,9 @@
     <Content Include="Fonts\TrueType\google-simple-doc.ttf">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
+    <Content Include="Fonts\TrueType\issue-258-corrupt-name-table.ttf">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
     <Content Include="Fonts\TrueType\PMingLiU.ttf">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>

src/UglyToad.PdfPig/Tokenization/Scanner/PdfTokenScanner.cs

@@ -688,6 +688,11 @@
                 return result;
             }
 
+            if (offset == 0 && reference.Generation > ushort.MaxValue)
+            {
+                return new ObjectToken(offset, reference, NullToken.Instance);
+            }
+
             Seek(offset);
 
             if (!MoveNext())