From d76c40a43a85f3ff82bdbc05f577fe7236095939 Mon Sep 17 00:00:00 2001
From: Brian Popow <popow@gmx.de>
Date: Mon, 21 Feb 2022 14:39:10 +0100
Subject: [PATCH] Ignore invalid gamma chunks

---
 src/ImageSharp/Formats/Png/PngDecoderCore.cs          | 3 ++-
 src/ImageSharp/Formats/Png/PngThrowHelper.cs          | 3 ---
 tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs | 5 ++---
 3 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/src/ImageSharp/Formats/Png/PngDecoderCore.cs b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
index 090e1e2b0..60437e015 100644
--- a/src/ImageSharp/Formats/Png/PngDecoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
@@ -432,7 +432,8 @@ namespace SixLabors.ImageSharp.Formats.Png
         {
             if (data.Length < 4)
             {
-                PngThrowHelper.ThrowInvalidGamma();
+                // Ignore invalid gamma chunks.
+                return;
             }
 
             // For example, a gamma of 1/2.2 would be stored as 45455.
diff --git a/src/ImageSharp/Formats/Png/PngThrowHelper.cs b/src/ImageSharp/Formats/Png/PngThrowHelper.cs
index 07372dae2..ae7d16ec7 100644
--- a/src/ImageSharp/Formats/Png/PngThrowHelper.cs
+++ b/src/ImageSharp/Formats/Png/PngThrowHelper.cs
@@ -24,9 +24,6 @@ namespace SixLabors.ImageSharp.Formats.Png
         [MethodImpl(InliningOptions.ColdPath)]
         public static void ThrowMissingPalette() => throw new InvalidImageContentException("PNG Image does not contain a palette chunk");
 
-        [MethodImpl(InliningOptions.ColdPath)]
-        public static void ThrowInvalidGamma() => throw new InvalidImageContentException("PNG Image does not contain enough data for the gamma chunk");
-
         [MethodImpl(InliningOptions.ColdPath)]
         public static void ThrowInvalidChunkType() => throw new InvalidImageContentException("Invalid PNG data.");
 
diff --git a/tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs
index 7fd87258b..0af5d9995 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs
@@ -283,7 +283,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
 
         [Theory]
         [WithFile(TestImages.Png.Bad.InvalidGammaChunk, PixelTypes.Rgba32)]
-        public void Decode_InvalidGammaChunk_ThrowsException<TPixel>(TestImageProvider<TPixel> provider)
+        public void Decode_InvalidGammaChunk_Ignored<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             Exception ex = Record.Exception(
@@ -292,8 +292,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
                     using Image<TPixel> image = provider.GetImage(PngDecoder);
                     image.DebugSave(provider);
                 });
-            Assert.NotNull(ex);
-            Assert.Contains("PNG Image does not contain enough data for the gamma chunk", ex.Message);
+            Assert.Null(ex);
         }
 
         [Theory]