Handle partial EXR scanline blocks

src/ImageSharp/Formats/Exr/Compression/Decompressors/B44ExrCompression.cs

@@ -39,7 +39,7 @@ internal class B44ExrCompression : ExrBaseDecompressor
     }
 
     /// <inheritdoc/>
-    public override void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer)
+    public override void Decompress(BufferedReadStream stream, uint compressedBytes, uint uncompressedBytes, Span<byte> buffer)
     {
         Span<ushort> outputBuffer = MemoryMarshal.Cast<byte, ushort>(buffer);
         Span<ushort> decompressed = this.tmpBuffer.GetSpan();

src/ImageSharp/Formats/Exr/Compression/Decompressors/NoneExrCompression.cs

@@ -25,10 +25,10 @@ internal class NoneExrCompression : ExrBaseDecompressor
     }
 
     /// <inheritdoc/>
-    public override void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer)
+    public override void Decompress(BufferedReadStream stream, uint compressedBytes, uint uncompressedBytes, Span<byte> buffer)
     {
-        int bytesRead = stream.Read(buffer, 0, Math.Min(buffer.Length, (int)this.BytesPerBlock));
-        if (bytesRead != (int)this.BytesPerBlock)
+        int bytesRead = stream.Read(buffer[..(int)uncompressedBytes]);
+        if (bytesRead != uncompressedBytes)
         {
             ExrThrowHelper.ThrowInvalidImageContentException("Could not read enough pixel data from the stream!");
         }

src/ImageSharp/Formats/Exr/Compression/Decompressors/Pxr24Compression.cs

@@ -39,19 +39,20 @@ internal class Pxr24Compression : ExrBaseDecompressor
     }
 
     /// <inheritdoc/>
-    public override void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer)
+    public override void Decompress(BufferedReadStream stream, uint compressedBytes, uint uncompressedBytes, Span<byte> buffer)
     {
-        Span<byte> uncompressed = this.tmpBuffer.GetSpan();
+        uint rowCount = uncompressedBytes / this.BytesPerRow;
+        uint packedBytes = this.pixelType == ExrPixelType.Float ? (uncompressedBytes / 4) * 3 : uncompressedBytes;
+        Span<byte> uncompressed = this.tmpBuffer.GetSpan()[..(int)packedBytes];
         Span<ushort> outputBufferHalf = MemoryMarshal.Cast<byte, ushort>(buffer);
         Span<uint> outputBufferFloat = MemoryMarshal.Cast<byte, uint>(buffer);
         Span<uint> outputBufferUint = MemoryMarshal.Cast<byte, uint>(buffer);
 
-        uint uncompressedBytes = this.BytesPerBlock;
-        UndoZipCompression(stream, compressedBytes, uncompressed, uncompressedBytes);
+        UndoZipCompression(stream, compressedBytes, uncompressed, packedBytes);
 
         int lastIn = 0;
         int outputOffset = 0;
-        for (int y = 0; y < this.RowsPerBlock; y++)
+        for (uint y = 0; y < rowCount; y++)
         {
             for (int c = 0; c < this.channelCount; c++)
             {

src/ImageSharp/Formats/Exr/Compression/Decompressors/RunLengthExrCompression.cs

@@ -26,7 +26,7 @@ internal class RunLengthExrCompression : ExrBaseDecompressor
         : base(allocator, bytesPerBlock, bytesPerRow, rowsPerBlock, width) => this.tmpBuffer = allocator.Allocate<byte>((int)bytesPerBlock);
 
     /// <inheritdoc/>
-    public override void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer)
+    public override void Decompress(BufferedReadStream stream, uint compressedBytes, uint uncompressedBytes, Span<byte> buffer)
     {
         Span<byte> uncompressed = this.tmpBuffer.GetSpan();
         int maxLength = (int)this.BytesPerBlock;

src/ImageSharp/Formats/Exr/Compression/Decompressors/ZipExrCompression.cs

@@ -26,15 +26,14 @@ internal class ZipExrCompression : ExrBaseDecompressor
         : base(allocator, bytesPerBlock, bytesPerRow, rowsPerBlock, width) => this.tmpBuffer = allocator.Allocate<byte>((int)bytesPerBlock);
 
     /// <inheritdoc/>
-    public override void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer)
+    public override void Decompress(BufferedReadStream stream, uint compressedBytes, uint uncompressedBytes, Span<byte> buffer)
     {
-        Span<byte> uncompressed = this.tmpBuffer.GetSpan();
+        Span<byte> uncompressed = this.tmpBuffer.GetSpan()[..(int)uncompressedBytes];
 
-        uint uncompressedBytes = (uint)buffer.Length;
         int totalRead = UndoZipCompression(stream, compressedBytes, uncompressed, uncompressedBytes);
 
-        Reconstruct(uncompressed, (uint)totalRead);
-        Interleave(uncompressed, (uint)totalRead, buffer);
+        Reconstruct(uncompressed, uncompressedBytes);
+        Interleave(uncompressed, uncompressedBytes, buffer);
     }
 
     /// <inheritdoc/>

src/ImageSharp/Formats/Exr/Compression/ExrBaseDecompressor.cs

@@ -31,8 +31,9 @@ internal abstract class ExrBaseDecompressor : ExrBaseCompression
     /// </summary>
     /// <param name="stream">The buffered stream to decompress.</param>
     /// <param name="compressedBytes">The compressed bytes.</param>
+    /// <param name="uncompressedBytes">The expected byte count for the current block.</param>
     /// <param name="buffer">The buffer to write the decompressed data to.</param>
-    public abstract void Decompress(BufferedReadStream stream, uint compressedBytes, Span<byte> buffer);
+    public abstract void Decompress(BufferedReadStream stream, uint compressedBytes, uint uncompressedBytes, Span<byte> buffer);
 
     /// <summary>
     /// Decompresses zip compressed data.
@@ -67,9 +68,9 @@ internal abstract class ExrBaseDecompressor : ExrBaseCompression
             totalRead += bytesRead;
         }
 
-        if (totalRead != uncompressedBytes)
+        if (totalRead != uncompressedBytes || dataStream.ReadByte() != -1)
         {
-            ExrThrowHelper.ThrowInvalidImageContentException("Could not read enough data for zip compressed EXR image data!");
+            ExrThrowHelper.ThrowInvalidImageContentException("ZIP compressed EXR block has an invalid decompressed length.");
         }
 
         return totalRead;

src/ImageSharp/Formats/Exr/ExrDecoderCore.cs

@@ -193,9 +193,16 @@ internal sealed class ExrDecoderCore : ImageDecoderCore
             this.ValidateChunkOffset(rowOffset, stream);
             stream.Position = (long)rowOffset;
             uint rowStartIndex = this.ReadUnsignedInteger(stream);
+            if (rowStartIndex >= height)
+            {
+                ExrThrowHelper.ThrowInvalidImageContentException("EXR chunk row index is outside the data window.");
+            }
 
             uint compressedBytesCount = this.ReadUnsignedInteger(stream);
-            decompressor.Decompress(stream, compressedBytesCount, decompressedPixelData);
+            uint rowsInBlock = Math.Min(rowsPerBlock, (uint)height - rowStartIndex);
+            uint uncompressedBytesCount = (uint)(bytesPerRow * rowsInBlock);
+
+            decompressor.Decompress(stream, compressedBytesCount, uncompressedBytesCount, decompressedPixelData);
 
             int offset = 0;
             for (uint rowIndex = rowStartIndex; rowIndex < rowStartIndex + rowsPerBlock && rowIndex < height; rowIndex++)
@@ -274,9 +281,16 @@ internal sealed class ExrDecoderCore : ImageDecoderCore
             this.ValidateChunkOffset(rowOffset, stream);
             stream.Position = (long)rowOffset;
             uint rowStartIndex = this.ReadUnsignedInteger(stream);
+            if (rowStartIndex >= height)
+            {
+                ExrThrowHelper.ThrowInvalidImageContentException("EXR chunk row index is outside the data window.");
+            }
 
             uint compressedBytesCount = this.ReadUnsignedInteger(stream);
-            decompressor.Decompress(stream, compressedBytesCount, decompressedPixelData);
+            uint rowsInBlock = Math.Min(rowsPerBlock, (uint)height - rowStartIndex);
+            uint uncompressedBytesCount = (uint)(bytesPerRow * rowsInBlock);
+
+            decompressor.Decompress(stream, compressedBytesCount, uncompressedBytesCount, decompressedPixelData);
 
             int offset = 0;
             for (uint rowIndex = rowStartIndex; rowIndex < rowStartIndex + rowsPerBlock && rowIndex < height; rowIndex++)

tests/ImageSharp.Tests/Formats/Exr/ExrZipDecoderTests.cs

@@ -33,7 +33,7 @@ public class ExrZipDecoderTests
 
     private static byte[] BuildExr(byte[] compressed)
     {
-        const int width = 64;
+        const int width = 256;
         const int height = 1;
 
         using MemoryStream output = new();