High memory usage when loading specific GIF

[rbottema]

I have noticed that loading the following GIF causes a large memory spike:

The GIF is 512 KB, but loading it seems to use 9~10GB of memory on my local (Windows) machine. Our Azure web app crashes with an OutOfMemoryException because of this, as it does not have such memory available. Here is the code I used to reproduce:

#:package SixLabors.ImageSharp@3.1.12

await using FileStream inStream = new("path\\to\\the.gif", FileMode.Open, FileAccess.Read);
var image = await SixLabors.ImageSharp.Image.LoadAsync(inStream);
image.Dispose();

I have verified the same behavior occurs with 4.0.0-alpha.0.71, if that's relevant.

Is this something that simply can happen when loading in certain images and if so, are there any guardrails we can use to protect us from this?

[JimBobSquarePants]

We have per-allocation guardrails and am looking at implementing accumulative ones but this seems like a bug to me. I’ll do some investigating.

[antonfirsov]

As the other comment mentions 8332 * 2082 * 153 * 32 bits = 10.6 GB, so strictly speaking no "bug" here but this is a zip bomb, meaning we should really address #2850, preferably with a fix also including 3.1.

I'm still gathering my thoughts for a proper feedback on #3056, but after refreshing my memory and paging in all the context, my opinion got stronger that capping total outstanding memory is not the way to go.

[JimBobSquarePants]

Identify is the way to go.

[antonfirsov]

What are the dimensions and the frame count of the gif? Can you share it?

[antonfirsov]

That, plus docs! I'll take a look.

[rbottema]

Thanks for confirmation on the approach!

I'm looking for implementing this protection and in our case the 'entry point' is in ImageSharp.Web through the Middleware. Looking at the code, there is no built-in way to hook in this validation, correct? The options I'm seeing are to add middleware that does the check (downside of loading images from twice on every (uncached) request with some logic duplication), leveraging HMAC in some way by doing the validation on URL generation time (not sure on the performance here), or preventing uploads of such images altogether (good idea in any case I guess, will need some extra code to check existing images). Will report back if I get around to getting this implemented.

[JimBobSquarePants]

You should be preventing them on upload. That's you first line of defense.

The middleware assumes images are already sanitized.

[JimBobSquarePants]

I've gone with ImageInfo.GetPixelMemorySize() See #3108