Backwards-compatible string encoding

[John Dennis]

Joshua Roys wrote:
> Hello all,
>
> I have just run into the problem that many of you have: trying to 
> parse the audit logs.
> Based on things other people have proposed, how does this sound:
> - hex-encode strings (and do not quote) if:
> -- contains non-ASCII or non-printable characters
> - quote strings if:
> -- contains whitespace or '=' or '"' (in which case you have to output 
> something like '\"'
> -- entirely {hex,octal,base10} characters
>
> What do you all think?
Your suggestion requires a kernel change. NAK on any change which 
preserves hex-encoded strings, it was a bad idea to begin with, it 
remains a bad idea.

The reason why kernel audit output has not changed is fear of breaking 
current user space code. However it's been often stated the only code 
which is supposed to directly parse audit output is code from the audit 
package (e.g. auparse, etc.).

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.



-- 
John Dennis <jdennis at redhat.com>

Looking to carve out IT costs?
www.redhat.com/carveoutcosts/