Backwards-compatible string encoding

[Joshua Roys]

On 03/27/2009 12:41 PM, John Dennis wrote:
> Strings should be formatted as strings which means enclosed in double
> quotes with standard C99 escaping.
>
> As it stands now the audit libraries have hard coded lists of every
> field the kernel can emit in an audit message. The test for decoding hex
> strings is based on whether the field is known to be a string. Field
> values *never* currently begin with a quote. If the kernel audit code
> was modified to format strings such that they are always enclosed in
> quotes the following positive things would occur:
>
> * No need for hard coded list of which fields are string values.
>
> * As long as the audit libraries are used for parsing it's fully
> backwards compatible (because during parsing you first look for a quote,
> if it's there you know its a string value, otherwise fall back to the
> legacy logic).
>
> * Strings are always human readable and it's obvious what is a string.
>
> * C99 string encoding is trivial and extremely efficient so there is no
> burden on the kernel.
>
> All in all a win/win situation.
>
>
>

Hello all,

The following is to provoke discussion; this is an issue I would like to 
see fixed, and I have the time to work on it at present.

Attached is a C program that has 2 output formats depending on a global 
flag (you can change the flag by incrementing argc).  I use it to 
demonstrate 2 options, but if one were picked, it could be used to 
preserve backwards compatibility via a proc file.  The binary format and 
API are inspired from both an email by Paul Moore:
  https://www.redhat.com/archives/linux-audit/2008-January/msg00087.html
extprot, a self-describing binary encoding:
  http://eigenclass.org/R2/writings/extprot-extensible-protocols-intro
and some SSH buffer management code I wrote.  Oh, and it should look 
suspiciously similar to some current audit code.

The text output is basically what John Dennis was looking for, I think. 
  Although I don't quote numbers or do any radix prefixing right now. 
Anyway.  Comments?  Anything I should change?  Is this worth pursuing at 
all (does something like this have any hope of being integrated)?

$ gcc testformat.c
$ ./a.out
(binary display via xxd)
$ ./a.out q
(text output)

One last thing: as you can see, the 3rd key/value pair msg='...' has 
key/value pairs inside it, kind of like the current setup where audit 
gets stuff from other code.  It has a k/v user_said=\'...\'...\' with a 
quote in the middle.  Basically, I would also like to being some sanity 
to users of audit, even though that may be insanely difficult, as has 
been mentioned.  Perhaps only exposing the k/v interface to them. 
Something.  Anything.

Thanks,

Joshua Roys
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