Re: [PATCH 2/2] conntrack: snprintf: add connlabel format specifier

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Fri, Jun 21, 2013 at 12:31:14AM +0200, Florian Westphal wrote:
> Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > On Tue, Jun 18, 2013 at 10:54:22PM +0200, Florian Westphal wrote:
> > > by default, nfct_snprintf will not resolve connlabel names, as they're
> > > system specific. This adds a fmt attribute to resolve names accordingly.
> > > 
> > > output looks like this:
> > > ... mark=0 use=1 labels=eth0-in (0),eth1-in (1)
> > > or
> > > <labels>
> > > <label name="eth0-in" bit="0"/>
> > > <label name="eth1-in" bit="1"/>
> > > </labels>
> > 
> > I think that the bit field is meaningless, so I would just export the
> > strings. I'd use:
> > 
> > <labels>
> > <label>eth0-in</label>
> > <label>eth1-in</label>
> > <labels>
> > 
> > I'd rather use elements, attributes are not easily extensible IMO.
> 
> Okay, I'll change it accordingly.  In case translation fails i'll put
> the number in there, so you'd get <label>(42)</label> if bit 42 is set
> but has no mapping entry.

I think we should not show it in case no mapping file is found. It
would be similar to the unclear usecase we discussed in the previous
patch.

> > > Major stupidity:
> > > As names can be anything, we need to be careful, especially when
> > > creating XML output. Only alphanumerical label names are printed at
> > > this time.
> > 
> > Hm, the string is enclosed between commas, isn't that enough to avoid
> > troubles?
> 
> What if connlabel.conf contains line like
> 0  foo<bar>&;!"

OK, let's just stick to alphanum for simplicity, that's so insane that
we'll make a better world if we prevent people using that ;-)

> > >  a) the chosen xml representation
> > >  b) wheter it makes sense to limit valid charactes in the label
> > >     names this way (e.g., should we care? should be disallow that
> > >     in iptables as well, etc).
> > >  c) if this patch makes sense in the first place, e.g, can't use
> > >      alternate mapping file for labels with nfct_snprintf
> > 
> > Regarding c) I think it makes sense. You can add some
> > nfct_set_connlabel_file interface to set where to find it, it's a bit
> > cheating but should resolve the issue.
> 
> Yuck ;-)
> 
> Lets ignore it for now, adding that would break thread-safety.
> I guess one alternative would be to add
> 
> nfct_labelmap_snprintf(char *buf,
> 	       	       size_t sz,
> 		       const struct nfct_labelmap *,
> 		       const struct nfct_bitmask *, int flags);
> 
> When a use case presents itself.

That's fine with me. The first use case would be the conntrack
utility, which should output the connlabel strings in they are being
used and the mapping file is available.

> > > +/*
> > > + * Labels can have any name, there are no restrictions.
> > > + * We will only print alpha numerical ones; else parsers
> > > + * could choke when putinng "&>" and friends into output
> > > + * (especially when using XML format).  ASCII machines only.
> > > + */
> > > +static bool label_is_sane(const char *label)
> > > +{
> > > +	for (;*label; label++) {
> > > +		if (*label >= 'a' && *label <= 'z')
> > > +			continue;
> > > +		if (*label >= 'A' && *label <= 'Z')
> > > +			continue;
> > > +		if (*label >= '0' && *label <= '9')
> > > +			continue;
> > 
> > is isalnum() instead?
> 
> I was intimidated by locale interactions of isalnum...

Ah, then just add a comment, it should be fine.