Add security warning about the from_pretrained() method
# What does this PR do?

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This PR adds a warning to the docs about the `from_pretrained()` method being susceptible to malicious code injection. This is similar to other warnings provided in the [PyTorch](https://pytorch.org/docs/stable/generated/torch.load.html#torch.load) and [Python](https://docs.python.org/3/library/pickle.html#module-pickle) docs.

For now I've put this in the autoclass tutorial, but can also put it in the API docs if we agree this makes sense.

Questions:

* Does the same issue apply to TensorFlow models?
* Does the [malware scanner](https://huggingface.co/docs/hub/security-malware) catch malicious code injection for _all_ Hub repos (public and private)?

h/t to @yk who pointed this out to me.

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Models:

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cc @sgugger @McPatate 

> Does the [malware scanner](https://huggingface.co/docs/hub/security-malware) catch malicious code injection for all Hub repos (public and private)?

It doesn't "catch malicious code injection" per se, it extracts the list of module-function pairs that can be called when unpickling. We still haven't implemented anything on top of that.

To answer your question, we're only scanning public repositories atm.<|||||>_The documentation is not available anymore as the PR was closed or merged._<|||||>Should a mention of the malware scanner also be added to the sentence? Right now it reads like using the Hub is a security issue whereas it's really `torch.load` that has a security issue; and the Hub enables verifying that the code is malware-free with both the malware scanner and signed commits.

I'd rather focus on showing how using the Hub is likely a smaller security risk than using an external tool like GDrive where no such verification can be done.<|||||>> Should a mention of the malware scanner also be added to the sentence? Right now it reads like using the Hub is a security issue whereas it's really `torch.load` that has a security issue; and the Hub enables verifying that the code is malware-free with both the malware scanner and signed commits.
> 
> I'd rather focus on showing how using the Hub is likely a smaller security risk than using an external tool like GDrive where no such verification can be done.

Good idea! Added a sentence about the scanner and reworded the text in [8098c4b](https://github.com/huggingface/transformers/pull/18801/commits/8098c4bede79f2e3f95308fbd47fd5b326f502e3)<|||||>I'm not disagreeing that the HF hub is a smaller risk compared to other things, just pointing out that the malware scanner currently lists my model as safe (and due to the mechanics of torch.save, it will always be evadable). And signed commits are super useful, but they don't mitigate this particular problem, as the signatory would be me, and therefore the signature valid.<|||||>> due to the mechanics of torch.save, it will always be evadable

@yk would you mind expanding on that ?<|||||>> @yk would you mind expanding on that ?

torch.save uses pickle, which in turn allows for arbitrary code execution. If the malware scanner detects loaded modules, I can simply un-load them after I've used them. If the malware scanner looks for the presence of certain instructions, strings, etc. I can always evade it somehow, that's just the nature of turing-completeness. I could probably even DDOS the malware scanner by just running an infinite loop. I'm happy to show more, and I'm going to, but I was waiting to release that info publicly before going through the responsible disclosure process here. DM me in case you want an early insight.<|||||>> If the malware scanner detects loaded modules, I can simply un-load them after I've used them.

I get the list of module-function pairs directly from the pickle opcodes ([`pickletools.genops`](https://docs.python.org/3/library/pickletools.html#pickletools.genops)), without executing anything. We went through some pretty [sophisticated exploits](https://ctftime.org/writeup/16723) and from what I saw when replicating there is always a trace of the module/function, e.g. if you wanted to run `eval` but alias it, you would still see the original `eval` reference.

> I could probably even DDOS the malware scanner by just running an infinite loop.

Since I'm going through the instruction list in the pickle file, there would be no DDOS possible via code execution. You could always generate a massive pickle file to bloat the scanner, but then you'd run into issues like uploading files to the hub before our scanner even goes through them + we can easily add heuristics to mark these files as inherently unsafe.

> If the malware scanner looks for the presence of certain instructions, strings, etc. I can always evade it somehow, that's just the nature of turing-completeness.

I'd like to see how you do that, happy to have the early insight, but I can wait for the public release :)

Note that you cannot serialize functions or lambdas in a pickle file, you can only execute functions that are in scope at deserialization time.

cc @adrinjalali

EDIT: thank you for expanding !<|||||>It seems there are actually ways to DDOS the scanner, we currently wouldn't catch the sploits [referenced here](https://github.com/moreati/pickle-fuzz#denial-of-service) (meaning we'd proceed to deserialization).<|||||>> I get the list of module-function pairs directly from the pickle opcodes

fair point, then I interpreted your previous statement in the wrong way. yea that could actually work to mitigate some of these things. At this time, my model here is still marked as safe, though: https://huggingface.co/ykilcher/totally-harmless-model/tree/main<|||||>> At this time, my model here is still marked as safe, though: https://huggingface.co/ykilcher/totally-harmless-model/tree/main

That's normal, at the time we haven't implemented any checks per se, we just extract the data from the pickles on the hub.

(coming soon)<|||||>> Should a mention of the malware scanner also be added to the sentence? Right now it reads like using the Hub is a security issue whereas it's really torch.load that has a security issue; and the Hub enables verifying that the code is malware-free with both the malware scanner and signed commits.

@LysandreJik saving and loading pickle files is only insecure if the author is not _trusted_, which is the case for the HF hub. The hub is a place where people share arbitrary pickle files, so it becomes a hub issue. It wouldn't be an issue if people kept using pickles from sources they trust. And the scanner doesn't really detect all vulnerabilities, and can't. For instance, when joblib does an `eval` on a given `n_jobs` parameter, there you could do whatever you want. In terms of signatures, we check signatures, but we don't check who the people behind the accounts are (and I don't think we should).

So I do think people should be wary when they load pickles from the hub.

Note that AFAIK in pretty much all major communities (like pytorch, sklearn, etc) people know about this and are working on having better solutions. But for now, users should be aware of the risks.<|||||>BTW @McPatate as discussed it would be awesome if we could write a post (or even some documentation) about what we currently know about pickle safety, and the potential next steps we are working on.

And maybe @yk you'd be interested in taking a look? Would be awesome to have your insights :)<|||||>@julien-c sure, I'm happy to contribute what I know<|||||>hi @yk the team (@McPatate in particular) wrote this document https://huggingface.co/docs/hub/security-pickle the doc's source is at https://github.com/huggingface/hub-docs/pull/294 – would love to get your feedback (including on the proposed solutions) Thanks! 