invert problem with multiport

invert problem with multiport

[Christoph Gossen]

Hello,

I think there's a bug in the behaviour of the multiport module - for
example, a line like

        iptables -p tcp -A OUTPUT -m multiport ! --dport 25 -j DROP

causes the same behaviour as

        iptables -p tcp -A OUTPUT -m multiport --dport 25 -j DROP

or

        iptables -p tcp -A OUTPUT --dport 25 -j DROP

and NOT (as one would expect) that one caused by

        iptables -p tcp -A OUTPUT ! --dport 25 -j DROP

Inverting the (set of) port(s) due to the "!" sign in the first line
above is just ignored
(no syntax error occures)!

Any comments?

Thanks,

Christoph

Re: invert problem with multiport

[Antony Stone]

On Tuesday 18 June 2002 4:50 pm, Christoph Gossen wrote:

> Hello,
>
> I think there's a bug in the behaviour of the multiport module - for
> example, a line like
>
>         iptables -p tcp -A OUTPUT -m multiport ! --dport 25 -j DROP
>
> causes the same behaviour as
>
>         iptables -p tcp -A OUTPUT -m multiport --dport 25 -j DROP
>
> or
>
>         iptables -p tcp -A OUTPUT --dport 25 -j DROP
>
> and NOT (as one would expect) that one caused by
>
>         iptables -p tcp -A OUTPUT ! --dport 25 -j DROP
>
> Inverting the (set of) port(s) due to the "!" sign in the first line
> above is just ignored
> (no syntax error occures)!
>
> Any comments?

I don't use the multiport match myself, but I'd expect it to be:

iptables -p tcp -A OUTPUT -m multiport --dport ! 25 -j DROP

In other words "a destination port which isn't 25"....

What does that do for you ?

I note from the man page for iptables, though, that --dport has the [ ! ] 
option, but "multiport --dport" doesn't, so maybe negating multiports is not 
supported at all ?

If you enter all the above rules, what do you get from

iptables -L OUTPUT -v -n ?

 

Antony.

Re: invert problem with multiport

[Christoph Gossen]

Antony Stone wrote:
> 
> On Tuesday 18 June 2002 4:50 pm, Christoph Gossen wrote:
> 
> > Hello,
> >
> > I think there's a bug in the behaviour of the multiport module - for
> > example, a line like
> >
> >         iptables -p tcp -A OUTPUT -m multiport ! --dport 25 -j DROP
> >
> > causes the same behaviour as
> >
> >         iptables -p tcp -A OUTPUT -m multiport --dport 25 -j DROP
> >
> > or
> >
> >         iptables -p tcp -A OUTPUT --dport 25 -j DROP
> >
> > and NOT (as one would expect) that one caused by
> >
> >         iptables -p tcp -A OUTPUT ! --dport 25 -j DROP
> >
> > Inverting the (set of) port(s) due to the "!" sign in the first line
> > above is just ignored
> > (no syntax error occures)!
> >
> > Any comments?
> 
> I don't use the multiport match myself, but I'd expect it to be:
> 
> iptables -p tcp -A OUTPUT -m multiport --dport ! 25 -j DROP

I have already tried this - it causes a syntax error "invalid
port/service `!' specified"
(everything ok with this, to me).

> 
> In other words "a destination port which isn't 25"....
> 
> What does that do for you ?
> 
> I note from the man page for iptables, though, that --dport has the [ ! ]
> option, but "multiport --dport" doesn't, so maybe negating multiports is not
> supported at all ?

This is what I assume, too. However, the "!" should not be silently
ignored then
but rather a syntax error should arise (to avoid confusion, or even a
potential
source of error).

Hervé Eychenne wrote:
...
> multiport option is "--dports", not "--dport"...
> 
>  RV

This is not quite right, as one can abbreviate down to even "--dp" (I
guess THIS
is really a intended feature and not a bug).

I forgot to mention the iptables version I tried: It was version 1.2.2
and 1.2.6a.


Greetings,

Christoph

RE: invert problem with multiport

[Stewart Thompson]

Hi Christoph:

	I am still running iptables 1.24. However, in that version I
don't think it supported the ! negation on multiport. Later versions
may have added that capability. Perhaps one of the members of
the list has a more definitive answer.

Stu...............



-----Original Message-----
From: netfilter-admin@lists.samba.org
[mailto:netfilter-admin@lists.samba.org]On Behalf Of Christoph Gossen
Sent: June 18, 2002 8:50 AM
To: netfilter@lists.samba.org
Subject: invert problem with multiport

Hello,

I think there's a bug in the behaviour of the multiport module - for
example, a line like

        iptables -p tcp -A OUTPUT -m multiport ! --dport 25 -j DROP

causes the same behaviour as

        iptables -p tcp -A OUTPUT -m multiport --dport 25 -j DROP

or

        iptables -p tcp -A OUTPUT --dport 25 -j DROP

and NOT (as one would expect) that one caused by

        iptables -p tcp -A OUTPUT ! --dport 25 -j DROP

Inverting the (set of) port(s) due to the "!" sign in the first line
above is just ignored
(no syntax error occures)!

Any comments?

Thanks,

Christoph