Disallow allocation attempts of unrepresentable sizes

src/ImageSharp/Memory/Allocators/UniformUnmanagedMemoryPoolMemoryAllocator.cs

@@ -117,6 +117,11 @@ internal sealed class UniformUnmanagedMemoryPoolMemoryAllocator : MemoryAllocato
         AllocationOptions options = AllocationOptions.None)
     {
         long totalLengthInBytes = totalLength * Unsafe.SizeOf<T>();
+        if (totalLengthInBytes < 0)
+        {
+            throw new InvalidMemoryOperationException("Attempted to allocate a MemoryGroup of a size that is not representable.");
+        }
+
         if (totalLengthInBytes <= this.sharedArrayPoolThresholdInBytes)
         {
             var buffer = new SharedArrayPoolBuffer<T>((int)totalLength);

tests/ImageSharp.Tests/Image/ImageTests.cs

@@ -6,6 +6,7 @@ using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Jpeg;
 using SixLabors.ImageSharp.Formats.Png;
+using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Tests.Memory;
@@ -35,6 +36,10 @@ public partial class ImageTests
             }
         }
 
+        [Fact]
+        public void Width_Height_SizeNotRepresentable_ThrowsInvalidImageOperationException()
+            => Assert.Throws<InvalidMemoryOperationException>(() => new Image<Rgba32>(int.MaxValue, int.MaxValue));
+
         [Fact]
         public void Configuration_Width_Height()
         {

tests/ImageSharp.Tests/Memory/Allocators/UniformUnmanagedPoolMemoryAllocatorTests.cs

@@ -107,6 +107,13 @@ public class UniformUnmanagedPoolMemoryAllocatorTests
         }
     }
 
+    [Fact]
+    public void AllocateGroup_SizeInBytesOverLongMaxValue_ThrowsInvalidMemoryOperationException()
+    {
+        var allocator = new UniformUnmanagedMemoryPoolMemoryAllocator(null);
+        Assert.Throws<InvalidMemoryOperationException>(() => allocator.AllocateGroup<S4>(int.MaxValue * (long)int.MaxValue, int.MaxValue));
+    }
+
     [Fact]
     public unsafe void Allocate_MemoryIsPinnableMultipleTimes()
     {