Ensure we do not leak bitmaps when parsing invalid PNG files.

OpenRA.Game/FileFormats/PngLoader.cs

@@ -42,6 +42,8 @@ namespace OpenRA.FileFormats
 				Color[] palette = null;
 				var data = new List<byte>();
 
+				try
+				{
 					for (;;)
 					{
 						var length = IPAddress.NetworkToHostOrder(br.ReadInt32());
@@ -49,12 +51,18 @@ namespace OpenRA.FileFormats
 						var content = br.ReadBytes(length);
 						/*var crc = */br.ReadInt32();
 
+						if (bitmap == null && type != "IHDR")
+							throw new InvalidDataException("Invalid PNG file - header does not appear first.");
+
 						using (var ms = new MemoryStream(content))
 						using (var cr = new BinaryReader(ms))
 							switch (type)
 							{
 								case "IHDR":
 									{
+										if (bitmap != null)
+											throw new InvalidDataException("Invalid PNG file - duplicate header.");
+
 										var width = IPAddress.NetworkToHostOrder(cr.ReadInt32());
 										var height = IPAddress.NetworkToHostOrder(cr.ReadInt32());
 										var bitDepth = cr.ReadByte();
@@ -103,9 +111,6 @@ namespace OpenRA.FileFormats
 
 								case "IEND":
 									{
-									if (bitmap == null)
-										throw new InvalidDataException("Image header not found.");
-
 										var bits = bitmap.LockBits(bitmap.Bounds(),
 											ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);
 
@@ -152,6 +157,13 @@ namespace OpenRA.FileFormats
 							}
 					}
 				}
+				catch
+				{
+					if (bitmap != null)
+						bitmap.Dispose();
+					throw;
+				}
+			}
 		}
 
 		static byte UnapplyFilter(PngFilter f, byte x, byte a, byte b, byte c)