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[cloud] Add ability to retrieve Google Compute Engine metadata

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For some unspecified "security" reason, the Google Compute Engine
metadata server will refuse any requests that do not include the
non-standard HTTP header "Metadata-Flavor: Google".

Attempt to autodetect such requests (by comparing the hostname against
"metadata.google.internal"), and add the "Metadata-Flavor: Google"
header if applicable.

Enable this feature in the CONFIG=cloud build, and include a sample
embedded script allowing iPXE to boot from a script configured as
metadata via e.g.

  # Create shared boot image
  make bin/ipxe.usb CONFIG=cloud EMBED=config/cloud/gce.ipxe

  # Configure per-instance boot script
  gcloud compute instances add-metadata <instance> \
         --metadata-from-file ipxeboot=boot.ipxe

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2017-01-23 14:41:22 +00:00
parent 0dc4814ca8
commit de85336abb
5 changed files with 87 additions and 0 deletions
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72
src/net/tcp/httpgce.c Normal file
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/*
* Copyright (C) 2017 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*
* You can also choose to distribute this program under the terms of
* the Unmodified Binary Distribution Licence (as given in the file
* COPYING.UBDL), provided that you have satisfied its requirements.
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/**
* @file
*
* Google Compute Engine (GCE) metadata retrieval
*
* For some unspecified "security" reason, the Google Compute Engine
* metadata server will refuse any requests that do not include the
* non-standard HTTP header "Metadata-Flavor: Google".
*/
#include <strings.h>
#include <stdio.h>
#include <ipxe/http.h>
/** Metadata host name
*
* This is used to identify metadata requests, in the absence of any
* more robust mechanism.
*/
#define GCE_METADATA_HOST_NAME "metadata.google.internal"
/**
* Construct HTTP "Metadata-Flavor" header
*
* @v http HTTP transaction
* @v buf Buffer
* @v len Length of buffer
* @ret len Length of header value, or negative error
*/
static int http_format_metadata_flavor ( struct http_transaction *http,
char *buf, size_t len ) {
/* Do nothing unless this appears to be a Google Compute
* Engine metadata request.
*/
if ( strcasecmp ( http->request.host, GCE_METADATA_HOST_NAME ) != 0 )
return 0;
/* Construct host URI */
return snprintf ( buf, len, "Google" );
}
/** HTTP "Metadata-Flavor" header */
struct http_request_header http_request_metadata_flavor __http_request_header ={
.name = "Metadata-Flavor",
.format = http_format_metadata_flavor,
};