MS RFC 90: Enable/Disable Layers in OGC Web Services by IP Lists

Date:2013/02/14
Author:Tamas Szekeres
Contact:szekerest at gmail.com
Status:Accepted (2013/03/02), Implemented
Version:MapServer 6.3-dev

1. Overview

This RFC provides the option to enable or disable OWS layers by IP lists. The aim is to let the admin to define list of users, identified through their IPs to allow or deny access to one or more specific WxS layers.

2. Proposed Solution

This addition will provide 2 more parameters in the WEB/METADATA section of the mapfile and/or in the METADATA section of every single layer.

  • ows_allowed_ip_list: contains the list of the allowed ip addresses or ranges
  • ows_denied_ip_list: contains the list of the denied ip addresses or ranges

These parameters support both a list of addresses from a file, or the ability to provide the values directly in the mapfile, in the cases where there are only a couple of IPs or ranges to be specified.

When setting the IP list inline, we can use spaces as separators, like:

LAYER
  METADATA
    "ows_allowed_ip_list" "123.45.67.89 11.22.33.44"
  END
END

Or we can specify a file containing the list of the IP addresses (IPs and ranges in the file are separated by spaces or newlines)

LAYER
  METADATA
    "ows_allowed_ip_list" "file:/path/to/list_of_ips.txt"
  END
END

We can also specify IP ranges using the CIDR notation , like: “192.168.1.0/24”

Setting ows_allowed_ip_list will deny all other IPs not specified in the list, and setting ows_denied_ip_list will allow all other IPs not specified in the list. When we both allow and deny a given IP the denial will take precedence.

The setting of ows_enable_request (added in MS RFC 67) will also be taken into account. Disabled requests cannot be re-enabled by IP lists, however we can restrict the access to a subset of layes by IP lists within the enabled OGC web services.

We will also be able to use the corresponding service specific settings (like wms_allowed_ip_list or wfs_allowed_ip_list)

This addition will support using both ipv4 and ipv6 IP addresses.

3. Disable the stock CGI operations

We also require to prevent the clients to work around the IP restrictions by using the stock CGI operations (mode=…). For this reason we add a new parameter to the WEB section of the mapfile (ms_enable_modes) to control which modes should be enabled. The ms_enable_modes will rely on the current implementetion of enable_request, so can use the asterisk ‘*’ to specify all modes and a preceding exclamation sign ‘!’ can be used to negate a given condition.

To retain the backwards compatibility, if we don’t specify the ms_enable_modes then all of the modes are enabled and dispatched.

When using OGC Web services, we don’t require to specify modes by the URL, so we can block all CGI modes by using the following setting:

WEB
  METADATA
        # Block all CGI modes by default for this mapfile
    "ms_enable_modes"  "!*"
  END
END

This will dispatch only those requests where explicit mode is not set by URL. It is suggested for all existing users to include this setting in the mapfiles if they intend to provide just OGC web services.

We’ll also be able to enable the modes selectively, as follows:

WEB
  METADATA
    # Enable Only MAP and LEGEND modes for this mapfile
    "ms_enable_modes" "!* MAP LEGEND"
      END
END

To enable all modes except MAP:

WEB
  METADATA
    # Enable all modes except MAP for this mapfile
    "ms_enable_modes" "!MAP"
      END
END

Given the mode specified by URL is disabled, MapServer will provide the following error message:

“The specified mode … is not supported by the current map configuration”

Within the scope of this RFC we don’t intend to support LAYER level setting of ms_enable_modes.

4. Implementation Details

This change will utilize the mechanism established in MS RFC 67, which makes the implementation fairly straightforward. Most of the functionality is provided by adding a new functions (msOWSIpDisabled, msOWSIpInMetadata, msOWSIpInList, msOWSIpParse) to mapows.c, to check whether a particular IP is disabled or not. The msOWSIpDisabled function is invoked from msOWSRequestIsEnabled and msOWSRequestLayersEnabled to prevent from adding the disabled layer to the enabled_layers list.

msOWSIpParse will parse the sting representation and the subnet into byte arrays. To test whether the IPs match, we make sure the following condition is true for each byte position

(ip1[i] & mask[i]) == (ip2[i] & mask[i])

The length of the byte array can be 4 (ipv4) or 16 (ipv6).

With regards to ipv6 we support both upper and lowercases in hex digits and support omitting the trailing zeros for each segment. We’ll also support te shorthand of subsequent segmens containing zeros by using double colons ‘::’ like: 2001:0db8::ff00:0042:8329 When parsing ipv6 we write each segment of the IPs and masks as unsigned shorts, which should work with both the big endian and little endian memory representations.

The setting ms_enable_modes will be implemented in msCGISetMode directly (in mapservutil.c). The implementation will explicitly call the current msOWSParseRequestMetadata function:

if (mapserv->Mode >= 0)
{
  int disabled = MS_FALSE;
  const char* enable_modes = msLookupHashTable(&mapserv->map->web.metadata, "ms_enable_modes");

  if (!msOWSParseRequestMetadata(enable_modes, mode, &disabled) && disabled) {
    /* the current mode is disabled */
    msSetError(MS_WEBERR, "The specified mode '%s' is not supported by the current map configuration", "msCGISetMode()", mode);
    return MS_FAILURE;
  }
}

5. Files Affected

  • mapows.c: Implement and call msOWSIpDisabled, msOWSIpInMetadata, msOWSIpInList, msOWSIpParse methods
  • mapservutil.c: Implement and ms_enable_modes logic

7. Backwards compatibility issues

None expected, new functionality.

8. Documentation

Within the scope of this addition we will also update the following documents:

  • SOS Server : Adding sos_allowed_ip_list, sos_denied_ip_list
  • WCS Server : Adding wcs_allowed_ip_list, wcs_denied_ip_list
  • WFS Server : Adding wfs_allowed_ip_list, wfs_denied_ip_list
  • WMS Server : Adding wms_allowed_ip_list, wms_denied_ip_list
  • MapFile/WEB : Adding ms_enable_modes in the WEB METADATA section

9. Sponsorship

Developed for Faunalia (http://www.faunalia.it) with funding from Regione Toscana - Settore SISTEMA INFORMATIVO TERRITORIALE ED AMBIENTALE”. For the project: “Sviluppo strumenti software per il trattamento di dati geografici basati su QuantumGIS e Postgis (CIG 0494241492)”

10. Voting history

Thomas Bonfort -0 Tom Kralidis +1 Daniel Morissette +1 Tamas Szekeres +1 Stephen Woodbridge +1