In the recent EEF SWG it was pointed out that function(2) has support for Enumerable protocol. While it’s obvious that “the vulnerability” can be exploited the same way with the Streams, what is still curious to me is the following. Why is there implementation for a such type in the first place? …

AFAIK Streams are just 2-ary functions, that is why Enumerable is implemented for them.

Nope iex(1)> 1..10 |> Stream.map(&(1+&1)) |> Map.get(:__struct__) Stream This is the whole point: when structs are present in the language, such thing is unnecessary.

Yes: iex(1)> Stream.unfold(5, fn ...(1)> 0 -> nil ...(1)> n -> {n, n - 1} ...(1)> end) |> is_function(2) true

Well that’s because this function in fact returns function(2) but not Stream: https://github.com/elixir-lang/elixir/blob/v1.10.2/lib/elixir/lib/stream.ex#L1524-L1527 As a proof: iex(4)> Stream.map(1..5, &(&1+1)) |> is_function(2) false Although it answers the question why defimpl for function(2)…

[image] arikai: While it’s obvious that “the vulnerability” can be exploited the same way with the Streams This is considered a vulnerability?

[image] arikai: While it’s obvious that “the vulnerability” can be exploited IMO “the vulnerability” here is deserializing untrusted data from ETF - the Enumerable protocol running 2-arity functions is only a way to escalate the impact of that vulnerability from a simple DoS (like you’d get w…

And even if there would be no defimpl for 2-ary functions, the problem would still be there, as nothing prevents user from encoding %Stream{enum: malicious_fun} to ETF.

[image] benwilson512: This is considered a vulnerability? Not at all: notice those quotes :slight_smile: @al2o3cr @hauleth It’s not about the possibility of running external (possibly malicious) code on you node without knowing it. I do acknowledge that there’re ways to do so as long as ther…

[image] arikai: What I’m asking is that there’s code that’s no longer needed with Streams present in stdlib. I think it’s a mistake to think of a Stream as a single kind of datastructure. What exists is an Enumerable protocol, and then Enum functions to consume those Enumerables eagerly, and …

[image] benwilson512: Elixir compatibility guarantees Now that’s the interesting part. I’ve failed to find any documentation for this behaviour. That is, to use function(2) as a first argument to function calls from Enum and Stream modules. And IF it is not documented: what compatibility gu…