Fix PNG chunk CRC validation (#241)

tests/SharpEmu.Libs.Tests/VideoOut/PngSplashLoaderTests.cs

@@ -0,0 +1,52 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.Libs.VideoOut;
+using Xunit;
+
+namespace SharpEmu.Libs.Tests.VideoOut;
+
+public sealed class PngSplashLoaderTests
+{
+    private const int IhdrCrcOffset = 29;
+    private const int IdatCrcOffset = 53;
+    private const int IendCrcOffset = 65;
+    private const string ValidRgbPng =
+        "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVR4nGMQMgkDAAD4AJ3MaiF4AAAAAElFTkSuQmCC";
+
+    [Theory]
+    [InlineData(IhdrCrcOffset)]
+    [InlineData(IdatCrcOffset)]
+    [InlineData(IendCrcOffset)]
+    public void TryLoadRejectsInvalidChunkCrc(int crcOffset)
+    {
+        var app0Root = Path.Combine(Path.GetTempPath(), $"sharpemu-png-{Guid.NewGuid():N}");
+        var sceSysPath = Path.Combine(app0Root, "sce_sys");
+        var pngPath = Path.Combine(sceSysPath, "pic0.png");
+        var previousApp0Root = Environment.GetEnvironmentVariable("SHARPEMU_APP0_DIR");
+
+        Directory.CreateDirectory(sceSysPath);
+        try
+        {
+            Environment.SetEnvironmentVariable("SHARPEMU_APP0_DIR", app0Root);
+
+            var png = Convert.FromBase64String(ValidRgbPng);
+            File.WriteAllBytes(pngPath, png);
+
+            Assert.True(PngSplashLoader.TryLoad(out var pixels, out var width, out var height));
+            Assert.Equal(1U, width);
+            Assert.Equal(1U, height);
+            Assert.Equal([0x56, 0x34, 0x12, 0xFF], pixels);
+
+            png[crcOffset] ^= 0x01;
+            File.WriteAllBytes(pngPath, png);
+
+            Assert.False(PngSplashLoader.TryLoad(out _, out _, out _));
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("SHARPEMU_APP0_DIR", previousApp0Root);
+            Directory.Delete(app0Root, recursive: true);
+        }
+    }
+}