[Oisf-devel] RFC: lua scripting flowvar access

[Vincent Fang]

Tested out this feature and was wondering if it's possible for it to store
a string into the flowvar? I attempted to test that out and kept getting
nil values from the ScFlowvarGet. The main goal is to find out and keep
track not only what portion of the flow the lua script is examining but
which flow it is for the administrator to see with that unique string var.

Vince


On Tue, Apr 23, 2013 at 6:07 AM, Victor Julien <victor at inliniac.net> wrote:

> On 04/22/2013 06:05 PM, Victor Julien wrote:
> > On 04/18/2013 06:01 PM, Victor Julien wrote:
> >> Funded by Emerging Threats, I've been working on giving the lua scripts
> >> access to flowvars.
> >>
> >> Currently only "flowvars" are done, "flowints" will be next. Please
> >> review the code at:
> >> https://github.com/inliniac/suricata/tree/dev-lua-flowvar
> >>
> >> Pcre based flowvar capturing is done in a post-match fashion. If the
> >> rule containing the "capture" matches, the var is stored in the flow.
> >>
> >> For lua scripting, this wasn't what the rule writers wanted. In this
> >> case, the flowvars are stored in the flow regardless of a rule match.
> >>
> >> The way a script can start using flowvars is by first registering which
> >> one it needs access to:
> >>
> >> function init (args)
> >>     local needs = {}
> >>     needs["http.request_headers.raw"] = tostring(true)
> >>     needs["flowvar"] = {"cnt"}
> >>     return needs
> >> end
> >>
> >> More than one can be registered, e.g.:
> >>
> >>     needs["flowvar"] = {"cnt", "somevar", "anothervar" }
> >>
> >> The maximum is 15 per script. The order of the vars matters. As Suricata
> >> uses id's internally, to use the vars you have to use id's as well. The
> >> first registered var has id 0, 2nd 1 and so on:
> >>
> >> function match(args)
> >>     a = ScFlowvarGet(0);
> >>     if a then
> >>         print ("We have an A: " .. (a))
> >>         a = tostring(tonumber(a)+1)
> >>         print ("A incremented to: " .. (a))
> >>         ScFlowvarSet(0, a, #a)
> >>     else
> >>         print "Init A to 1"
> >>         a = tostring(1)
> >>         ScFlowvarSet(0, a, #a)
> >>     end
> >>
> >>     print ("A is " .. (a))
> >>     if tonumber(a) == 23 then
> >>         print "Match!"
> >>         return 1
> >>     end
> >>
> >>     return 0
> >> end
> >>
> >> You can also use a var:
> >>
> >> function init (args)
> >>     local needs = {}
> >>     needs["http.request_headers.raw"] = tostring(true)
> >>     needs["flowvar"] = {"blah", "cnt"}
> >>     return needs
> >> end
> >>
> >> local var_cnt = 1
> >>
> >> function match(args)
> >>     a = ScFlowvarGet(var_cnt);
> >>     if a then
> >>         print ("We have an A: " .. (a))
> >>         a = tostring(tonumber(a)+1)
> >>         print ("A incremented to: " .. (a))
> >>         ScFlowvarSet(var_cnt, a, #a)
> >>     else
> >>         print "Init A to 1"
> >>         a = tostring(1)
> >>         ScFlowvarSet(var_cnt, a, #a)
> >>     end
> >>
> >>     print ("A is " .. (a))
> >>     if tonumber(a) == 23 then
> >>         print "Match!"
> >>         return 1
> >>     end
> >>
> >>     return 0
> >> end
> >>
> >> Flowvars are set at the end of the rule's inspection, so after the
> >> script has run.
> >>
> >> When multiple stores are done from the script and/or pcre, the last
> >> match will win. So if order matters, rule priority can be used to
> >> control inspection order.
> >>
> >> Thoughts, comments, and code review highly welcomed.
> >>
> >
> > Updated branch:
> > https://github.com/inliniac/suricata/tree/dev-lua-flowvar-v1.1
> >
> > - Adds flowint support:
> >
> > function init (args)
> >     local needs = {}
> >     needs["http.request_headers"] = tostring(true)
> >     needs["flowint"] = {"cnt"}
> >     return needs
> > end
> >
> > function match(args)
> >     a = ScFlowintGet(0);
> >     if a then
> >         ScFlowintSet(0, a + 1)
> >     else
> >         ScFlowintSet(0, 1)
> >     end
> >
> >     a = ScFlowintGet(0);
> >     if a == 23 then
> >         return 1
> >     end
> >
> >     return 0
> > end
> >
> > return 0
> >
> > Sets are real time, so are done regardless of script match or rule match.
> >
> > - Converts flowvar sets to real time, to fix some var overwrite issues
> > in HTTP header inspection.
> >
>
> https://github.com/inliniac/suricata/tree/dev-lua-flowvar-v1.2
>
> Adds in ScFlowintIncr & ScFlowintDecr. From the commit:
>
> "Add flowint lua functions for incrementing and decrementing flowints.
>
> First use creates the var and inits to 0. So a call:
>
>     a = ScFlowintIncr(0)
>
> Results in a == 1.
>
> If the var reached UINT_MAX (2^32), it's not further incremented. If the
> var reaches 0 it's not decremented further.
>
> Calling ScFlowintDecr on a uninitialized var will init it to 0.
>
> Example script:
>
>     function init (args)
>         local needs = {}
>         needs["http.request_headers"] = tostring(true)
>         needs["flowint"] = {"cnt_incr"}
>         return needs
>     end
>
>     function match(args)
>         a = ScFlowintIncr(0);
>         if a == 23 then
>             return 1
>         end
>
>         return 0
>     end
>     return 0
>
> This script matches the 23rd time it's invoked on a flow."
>
> --
> ---------------------------------------------
> Victor Julien
> http://www.inliniac.net/
> PGP: http://www.inliniac.net/victorjulien.asc
> ---------------------------------------------
>
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