From: Phil Sutter <phil@nwl.cc>
To: Fernando Fernandez Mancera <ffmancera@riseup.net>,
Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netfilter-devel@vger.kernel.org
Subject: Re: [PATCH nft v2 1/6] osf: add version fingerprint support
Date: Fri, 15 Mar 2019 11:03:33 +0100 [thread overview]
Message-ID: <20190315100333.GD3511@orbyte.nwl.cc> (raw)
In-Reply-To: <20190314201309.iqdyb7icreyyhhke@salvia> <20190314200737.erhjrhoaciclapsn@salvia> <27D82259-F921-48E0-A718-A08E2BCCAACD@riseup.net>
Hi,
Batching messages here since I'm apparently too slow in replying. :)
On Thu, Mar 14, 2019 at 07:24:23PM +0100, Fernando Fernandez Mancera wrote:
> El 14 de marzo de 2019 18:34:54 CET, Phil Sutter <phil@nwl.cc> escribió:
> >On Thu, Mar 14, 2019 at 02:58:40PM +0100, Pablo Neira Ayuso wrote:
> >> On Thu, Mar 14, 2019 at 12:14:23PM +0100, Fernando Fernandez Mancera
> >wrote:
> >> > I have been thinking more about this today. I don't know how access
> >to
> >> > the right-hand-side string from the kernel if it is possible. Sorry
> >if
> >> > the question is very dumb, but I may lack experience with the nft
> >> > registers and RHS data of an expression.
> >>
> >> I think you can hide flags from json, which is what Phil suggests, I
> >> mean, just infer version flags from the syntax, ie. if
> >> "genre::version" is used, then set of the version flag.
> >>
> >> I think Phil is not suggesting kernel changes.
>
> That makes sense to me.
In general, I think we should not deviate too much in both APIs. Also, a
bit more complicated syntax is less of a problem in JSON, while OTOH I
think spending a few extra cycles on keeping CLI syntax as simple as
possible is worth doing.
> >Assuming the above is correct, my suggestion of making the flag option
> >implicit does not quite hold, at least not without painful
> >postprocessing of relational statement in userspace.
> >
> >Right now this all seems to me like enabling multiple comparisons
> >within
> >a single relational, i.e. one for genre and the other for version.
> >Nftables doesn't quite do such things. E.g. matching on two TCP header
> >fields requires two relationals, e.g. 'tcp dport 22 tcp sport > 1024'.
> >Internally then, these two statements may be combined into a single
> >payload match if suitable.
>
> I think in this case we can't do that. In my opinion it doesn't make sense to evaluate only the version without the OS genre. Do you agree? Thanks!
Well, I guess we could but the question is indeed if we want to. In
general, I tend to leave the decision what makes sense and what not to
the user. Although a bit sloppy, something like 'osf version "XP"' might
be a valuable shortcut for some.
On Thu, Mar 14, 2019 at 09:07:37PM +0100, Pablo Neira Ayuso wrote:
> On Thu, Mar 14, 2019 at 06:34:54PM +0100, Phil Sutter wrote:
[...]
> > Actually I'm still in the process of understanding how all this works.
> > What I got so far is (correct me if I'm wrong): osf expr does the
> > fingerprinting and returns a string which relational expr compares to
> > right-hand side. This new version flag defines whether osf expr adds the
> > version to returned string or not.
> >
> > Assuming the above is correct, my suggestion of making the flag option
> > implicit does not quite hold, at least not without painful
> > postprocessing of relational statement in userspace.
> >
> > Right now this all seems to me like enabling multiple comparisons within
> > a single relational, i.e. one for genre and the other for version.
> > Nftables doesn't quite do such things. E.g. matching on two TCP header
> > fields requires two relationals, e.g. 'tcp dport 22 tcp sport > 1024'.
> > Internally then, these two statements may be combined into a single
> > payload match if suitable.
>
> The osf expression returns a string with the OS genre, and if the
> version flag is set on, it appends the version to this string, ie.
> genre + version.
>
> This allows us to build maps, ie.
>
> meta mark set osf genre { "linux" : 0x10, "windows" : 0x20, "macos" : 0x40 }
>
> But, with this new version, you could also do:
>
> meta mark set osf genre { "linux::4.0" : 0x11, "linux::3.0" : 0x12, ...}
>
> and so on.
>
> So I see this version thing as a extended matching.
>
> The osf engine actually _already_ finds a precise matching, ie. genre
> + version, since the fingerprint is per genre + version. But you can
> just decide to match on the genre (eg. linux).
The problem we're facing IMO is that nft_cmp is limited to a simple
memcmp(). This demands LHS to know what RHS contains. I'm not implying
it would be a good idea, but imagine nft_cmp could handle wildcards, we
could use "linux:*" to match on genre only, "linux:4.0:*" to match on
genre and version and even "linux:4.*" to match genre and major version
number.
Actually we might be able to implement the above by setting 'len' field
correctly.
> > Applying the same logic to osf expression, we would implement 'osf name
> > foo osf version 3.141' and add 'osf_try_merge()' routine to
> > 'rule_postprocess()' which tries to combine the two statements.
> > Obviously, this is quite a bit of extra work, not sure if feasible.
>
> I think the discussion here is the syntax, ie.
>
> osf genre "Linux::4.10"
>
> vs.
>
> osf genre "Linux" version "4.10"
>
> This only requires changes to the userspace nftables side, if you
> prefer this syntax, which is what I understand you would like to see,
> right?
Not quite. I like how osf is an expression, not a statement. This makes
things like 'osf name != "Linux"' possible. What I didn't like was how
the proposed extension requires users to input redundant info:
| osf name version "Linux:4.20"
RHS contains the version number, so LHS should not need to have
"version" explicitly stated.
On Thu, Mar 14, 2019 at 09:13:09PM +0100, Pablo Neira Ayuso wrote:
[...]
> I think we could even extend this later on to match things like:
>
> # Popular cluster config scripts disable timestamps and
> # selective ACK:
> S4:64:1:48:M1460,N,W0: Linux:2.4:cluster:Linux 2.4 in cluster
> ^^^^^^^^^^^^^^^^^
> Then, do:
>
> os gente "Linux:2.4:cluster"
>
> by adding a new flag to match the "Subtype" field (according to the
> file description in pf.os).
In an ideal world, we could match on any (combination of) fields in the
database. I am aware this is probably over-engineering. :)
What we could do though with little effort is to make use of the OS info
structure in database by making use of nft_cmp comparing only the first
'len' bytes of data in registers. My idea would be that:
* 'osf' expression always returns "full" data, i.e.: "OS:VER:SUB"
* nft_cmp compares that string to RHS up to RHS length
So let's assume DB lookup returns "Windows:2003:AS:", then:
osf name "Windows" -> match
osf name "Windows:" -> match
osf name "Windows:XP:" -> no match
osf name "Windows:2000:" -> no match
osf name "Windows:200" -> match
So we have optional version match and even a poor-man's wildcard
functionality. Specifying the trailing semi-colon implicitly causes an
exact match on the last field.
What do you think?
Cheers, Phil
next prev parent reply other threads:[~2019-03-15 10:03 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-11 15:14 [PATCH nft v2 1/6] osf: add version fingerprint support Fernando Fernandez Mancera
2019-03-11 15:14 ` [PATCH nft v2 2/6] json: osf: add version json support Fernando Fernandez Mancera
2019-03-11 15:14 ` [PATCH nft v2 3/6] tests: py: add osf tests with versions Fernando Fernandez Mancera
2019-03-11 15:14 ` [PATCH nft v2 4/6] doc: add osf version option to man page Fernando Fernandez Mancera
2019-03-11 15:14 ` [PATCH nft v2 5/6] files: osf: update pf.os with newer OS fingerprints Fernando Fernandez Mancera
2019-03-11 15:14 ` [PATCH nft v2 6/6] files: pf.os: merge the signatures spllited by version Fernando Fernandez Mancera
2019-03-13 9:44 ` [PATCH nft v2 1/6] osf: add version fingerprint support Phil Sutter
2019-03-13 10:14 ` Fernando Fernandez Mancera
2019-03-13 11:27 ` Phil Sutter
2019-03-13 14:15 ` Fernando Fernandez Mancera
2019-03-13 15:06 ` Phil Sutter
2019-03-13 15:22 ` Fernando Fernandez Mancera
2019-03-13 15:34 ` Phil Sutter
2019-03-13 16:46 ` Fernando Fernandez Mancera
2019-03-14 11:14 ` Fernando Fernandez Mancera
2019-03-14 13:58 ` Pablo Neira Ayuso
2019-03-14 17:34 ` Phil Sutter
2019-03-14 18:24 ` Fernando Fernandez Mancera
2019-03-15 10:03 ` Phil Sutter [this message]
2019-03-15 17:13 ` Pablo Neira Ayuso
2019-03-15 20:21 ` Fernando Fernandez Mancera
2019-03-16 9:05 ` Pablo Neira Ayuso
2019-03-17 17:10 ` Fernando Fernandez Mancera
2019-03-18 17:42 ` Phil Sutter
2019-03-19 11:06 ` Pablo Neira Ayuso
2019-03-20 13:46 ` Phil Sutter
2019-03-21 8:32 ` Pablo Neira Ayuso
2019-03-21 11:15 ` Phil Sutter
2019-03-21 11:18 ` Pablo Neira Ayuso
2019-03-21 14:06 ` Phil Sutter
2019-03-21 16:57 ` Pablo Neira Ayuso
2019-03-21 18:14 ` Phil Sutter
2019-03-14 20:07 ` Pablo Neira Ayuso
2019-03-14 20:13 ` [PATCH nft v2 1/6] osf: add version fingerprint supportg Pablo Neira Ayuso
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190315100333.GD3511@orbyte.nwl.cc \
--to=phil@nwl.cc \
--cc=ffmancera@riseup.net \
--cc=netfilter-devel@vger.kernel.org \
--cc=pablo@netfilter.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).