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

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

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.

> 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?

> Else you get
> labels=(0), .. or <labels><label name="" bit="0"/> in xml output.
> 
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  I am interested in feedback wrt.
> 
>  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.

>  include/internal/internal.h                        |  1 +
>  include/internal/prototypes.h                      |  1 +
>  .../libnetfilter_conntrack.h                       |  3 +
>  src/conntrack/snprintf_default.c                   | 84 +++++++++++++++++++++-
>  src/conntrack/snprintf_xml.c                       |  8 ++-
>  5 files changed, 93 insertions(+), 4 deletions(-)
> 
> diff --git a/include/internal/internal.h b/include/internal/internal.h
> index aaf6bd4..a5c7923 100644
> --- a/include/internal/internal.h
> +++ b/include/internal/internal.h
> @@ -6,6 +6,7 @@
>  #ifndef __LIBNETFILTER_CONNTRACK_INTERNAL__
>  #define __LIBNETFILTER_CONNTRACK_INTERNAL__
>  
> +#include <stdbool.h>
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <stdarg.h>
> diff --git a/include/internal/prototypes.h b/include/internal/prototypes.h
> index cc8de1d..577270b 100644
> --- a/include/internal/prototypes.h
> +++ b/include/internal/prototypes.h
> @@ -16,6 +16,7 @@ int __snprintf_proto(char *buf, unsigned int len, const struct __nfct_tuple *tup
>  int __snprintf_conntrack_default(char *buf, unsigned int len, const struct nf_conntrack *ct, const unsigned int msg_type, const unsigned int flags);
>  int __snprintf_conntrack_xml(char *buf, unsigned int len, const struct nf_conntrack *ct, const unsigned int msg_type, const unsigned int flags);
>  int __snprintf_connlabels(char *buf, unsigned int len, const struct nf_conntrack *ct, const char *prefix, const char *end);
> +int __snprintf_connlabels_names(char *buf, unsigned int len, const struct nf_conntrack *ct, const char *prefix, const char *end, bool xml);
>  
>  enum __nfct_addr {
>  	__ADDR_SRC = 0,
> diff --git a/include/libnetfilter_conntrack/libnetfilter_conntrack.h b/include/libnetfilter_conntrack/libnetfilter_conntrack.h
> index 39dc24c..eedf85e 100644
> --- a/include/libnetfilter_conntrack/libnetfilter_conntrack.h
> +++ b/include/libnetfilter_conntrack/libnetfilter_conntrack.h
> @@ -389,6 +389,9 @@ enum {
>  
>  	NFCT_OF_TIMESTAMP_BIT = 3,
>  	NFCT_OF_TIMESTAMP = (1 << NFCT_OF_TIMESTAMP_BIT),
> +
> +	NFCT_OF_CONNLABELS_BIT = 4,
> +	NFCT_OF_CONNLABELS = (1 << NFCT_OF_CONNLABELS_BIT),
>  };
>  
>  extern int nfct_snprintf(char *buf, 
> diff --git a/src/conntrack/snprintf_default.c b/src/conntrack/snprintf_default.c
> index a1edef4..7befbd7 100644
> --- a/src/conntrack/snprintf_default.c
> +++ b/src/conntrack/snprintf_default.c
> @@ -313,9 +313,89 @@ __snprintf_connlabels(char *buf, unsigned int len,
>  	return size;
>  }
>  
> +/*
> + * 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?

> +		if (*label == ' ' || *label == '-')
> +			continue;i
> +		return false;
> +	}
> +	return true;
> +}
> +
> +int
> +__snprintf_connlabels_names(char *buf, unsigned int len,
> +			    const struct nf_conntrack *ct,
> +			    const char *prefix, const char *end, bool xml)
> +{
> +	const struct nfct_bitmask *b = nfct_get_attr(ct, ATTR_CONNLABELS);
> +	unsigned int i, max;
> +	int ret, size = 0, offset = 0;
> +	struct nfct_labelmap *map;
> +
> +	if (!b)
> +		return 0;
> +	map = nfct_labelmap_new(NULL);
> +	if (!map)
> +		return __snprintf_connlabels(buf, len, ct, prefix, end);
> +
> +	ret = snprintf(buf, len, "%s", prefix);
> +	BUFFER_SIZE(ret, size, len, offset);
> +	max = nfct_bitmask_maxbit(b);
> +	for (i = 0; i <= max && len; i++) {
> +		const char *name;
> +		if (!nfct_bitmask_test_bit(b, i))
> +			continue;
> +		name = nfct_labelmap_get_name(map, i);
> +		if (!name || !label_is_sane(name))
> +			name = "";
> +
> +		if (xml)
> +			ret = snprintf(buf + offset, len, "<label name=\"%s\" ", name);
> +		else if (strcmp(name, "") != 0)
> +			ret = snprintf(buf + offset, len, "%s ", name);
> +		else
> +			ret = 0;
> +		BUFFER_SIZE(ret, size, len, offset);
> +
> +		if (xml)
> +			ret = snprintf(buf + offset, len, "bit=\"%u\"/>", i);
> +		else
> +			ret = snprintf(buf + offset, len, "(%u),", i);
> +		BUFFER_SIZE(ret, size, len, offset);
> +	}
> +
> +	nfct_labelmap_destroy(map);
> +	if (offset && end) {
> +		if (!xml) {
> +			offset--; /* remove last , */
> +			size--;
> +		}
> +		ret = snprintf(buf + offset, len, "%s", end);
> +		BUFFER_SIZE(ret, size, len, offset);
> +	}
> +	return size;
> +}
> +
>  static int
> -__snprintf_clabels(char *buf, unsigned int len, const struct nf_conntrack *ct)
> +__snprintf_clabels(char *buf, unsigned int len,
> +		   const struct nf_conntrack *ct, bool names)
>  {
> +	if (names)
> +		return  __snprintf_connlabels_names(buf, len, ct,
> +					   "labels=", " ", false);
>  	return __snprintf_connlabels(buf, len, ct, "labels=", " ");
>  }
>  
> @@ -458,7 +538,7 @@ int __snprintf_conntrack_default(char *buf,
>  	}
>  
>  	if (test_bit(ATTR_CONNLABELS, ct->head.set)) {
> -		ret = __snprintf_clabels(buf+offset, len, ct);
> +		ret = __snprintf_clabels(buf+offset, len, ct, flags & NFCT_OF_CONNLABELS );
>  		BUFFER_SIZE(ret, size, len, offset);
>  	}
>  
> diff --git a/src/conntrack/snprintf_xml.c b/src/conntrack/snprintf_xml.c
> index f373f5b..1c2440a 100644
> --- a/src/conntrack/snprintf_xml.c
> +++ b/src/conntrack/snprintf_xml.c
> @@ -349,8 +349,12 @@ static int __snprintf_tuple_xml(char *buf,
>  }
>  
>  static int
> -__snprintf_clabels_xml(char *buf, unsigned int len, const struct nf_conntrack *ct)
> +__snprintf_clabels_xml(char *buf, unsigned int len,
> +		       const struct nf_conntrack *ct, bool names)
>  {
> +	if (names)
> +		return __snprintf_connlabels_names(buf, len, ct,
> +				"<labels>", "</labels>", true);
>  	return __snprintf_connlabels(buf, len, ct, "<labels>", "</labels>");
>  }
>  
> @@ -440,7 +444,7 @@ int __snprintf_conntrack_xml(char *buf,
>  	}
>  
>  	if (test_bit(ATTR_CONNLABELS, ct->head.set)) {
> -		ret = __snprintf_clabels_xml(buf+offset, len, ct);
> +		ret = __snprintf_clabels_xml(buf+offset, len, ct, flags & NFCT_OF_CONNLABELS);
>  		BUFFER_SIZE(ret, size, len, offset);
>  	}
>  
> -- 
> 1.8.1.5
> 
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