Re: Backwards-compatible string encoding
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- hex-encode strings (and do not quote) if: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(a)redhat.com>
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