Pickled objects over the network

[Steve Holden]

Hendrik van Rooyen wrote:
> "Steve Holden" <steve at ho...eb.com> wrote:
> 
>> I think someone has already pointed out netstrings, which will allow you 
>> to send arbitrary strings over network connections deterministically. 
> 
> Yes I brought it up
> 
>> I'm afraid for the rest it's just a matter of encoding your information 
>> in a way that you can decode without allowing a malicious sender to 
>> cause arbitrary code to be called.
> 
> Yes - and in general you do this by having both the sender and the 
> transmitter conform to some pre agreed format - a netstring is one 
> of the simplest of such things - another way is to "frame" records 
> between some kind of delimeter and to "escape" the occurences of the
> delimiter in the data.  Another way is to use simple "self defining fields"
> that work by giving fields a "tag" number from a list of pre defined
> things, as well as a length, followed by the data - some financial 
> protocols work as a variant of this concept, where the presence or 
> absence of a bit signify the presence or absence of a field in the record.
> 
> The problem with all of these schemes is that they are all a PITA to
> implement, compared to the ease with which you can pickle and 
> unpickle something like a simple dict of parameters.
> 
> And if that is all you want to pass over to some remote thing, then
> having to download and import Pyro is an equal PITA and overkill.
> - It adresses a far more sophisticated problem than just getting 
> some small things across the network.
> 
> Now if Pyro were to make it into the standard library, it would be
> my method of choice for even this silly level of functionality, 
> because I happen to think it rocks.
> 
>> The issue with pickle is that it's way too general a mechanism to be 
>> secure in open network applications, so a suggestion to beef up its 
>> security was misguided. Trying to "beef up pickle's security" is like 
>> trying to make a shotgun that can't kill anything.
>>
> 
> Is it really that impossible to add something like a "noeval" flag, or to
> force it to only give you a string or a dict if you ask for one or the other, 
> given that someone has already mentioned that the built in types are 
> decoded by separate routines?
> 
> Or more generally - as it already has different protocols - to define a
> protocol that won't pass executable stuff over, or one that will only 
> pass and accept the built in types?
> 
Yes.

regards
  Steve
-- 
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