libvirt/src/network/leaseshelper.c
Michal Privoznik 876211ef4a leaseshelper: Wait to acquire PID file
On a DHCP transaction, dnsmasq runs our leases helper which
updates corresponding JSON files. While one dnsmasq won't run the
leaseshelper in parallel, two dnsmasqs (from two distinct
networks) might. To avoid corrupting JSON file, the leaseshelper
acquires PID file first. Well, the way it's acquiring it is not
ideal - it calls virPidFileAcquirePath(wait = false); which
means, that either it acquires the PID file instantly or returns
an error and does not touch the JSON at all. This in turn means
that there might be a leases record missing. With wait = true,
this won't happen.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1840307

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
2020-06-24 16:08:03 +02:00

257 lines
7.7 KiB
C

/*
* leaseshelper.c: Helper program to create custom leases file
*
* Copyright (C) 2014 Red Hat, Inc.
* Copyright (C) 2014 Nehal J Wani
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library. If not, see
* <http://www.gnu.org/licenses/>.
*
* For IPv6 support, use dnsmasq >= 2.67
*/
#include <config.h>
#include "virthread.h"
#include "virfile.h"
#include "virpidfile.h"
#include "virstring.h"
#include "virerror.h"
#include "viralloc.h"
#include "virjson.h"
#include "virlease.h"
#include "virenum.h"
#include "configmake.h"
#include "virgettext.h"
#include "virutil.h"
#define VIR_FROM_THIS VIR_FROM_NETWORK
static const char *program_name;
/* Display version information. */
static void
helperVersion(const char *argv0)
{
printf("%s (%s) %s\n", argv0, PACKAGE_NAME, PACKAGE_VERSION);
}
G_GNUC_NORETURN static void
usage(int status)
{
if (status) {
fprintf(stderr, _("%s: try --help for more details\n"), program_name);
} else {
printf(_("Usage: %s add|old|del|init mac|clientid ip [hostname]\n"
"Designed for use with 'dnsmasq --dhcp-script'\n"
"Refer to man page of dnsmasq for more details'\n"),
program_name);
}
exit(status);
}
/* Flags denoting actions for a lease */
enum virLeaseActionFlags {
VIR_LEASE_ACTION_ADD, /* Create new lease */
VIR_LEASE_ACTION_OLD, /* Lease already exists, renew it */
VIR_LEASE_ACTION_DEL, /* Delete the lease */
VIR_LEASE_ACTION_INIT, /* Tell dnsmasq of existing leases on restart */
VIR_LEASE_ACTION_LAST
};
VIR_ENUM_DECL(virLeaseAction);
VIR_ENUM_IMPL(virLeaseAction,
VIR_LEASE_ACTION_LAST,
"add", "old", "del", "init",
);
int
main(int argc, char **argv)
{
char *pid_file = NULL;
char *custom_lease_file = NULL;
const char *ip = NULL;
const char *mac = NULL;
const char *leases_str = NULL;
const char *iaid = getenv("DNSMASQ_IAID");
const char *clientid = getenv("DNSMASQ_CLIENT_ID");
const char *interface = getenv("DNSMASQ_INTERFACE");
const char *hostname = getenv("DNSMASQ_SUPPLIED_HOSTNAME");
char *server_duid = NULL;
int action = -1;
int pid_file_fd = -1;
int rv = EXIT_FAILURE;
bool delete = false;
virJSONValuePtr lease_new = NULL;
virJSONValuePtr leases_array_new = NULL;
virSetErrorFunc(NULL, NULL);
virSetErrorLogPriorityFunc(NULL);
program_name = argv[0];
if (virGettextInitialize() < 0 ||
virErrorInitialize() < 0) {
fprintf(stderr, _("%s: initialization failed\n"), program_name);
exit(EXIT_FAILURE);
}
/* Doesn't hurt to check */
if (argc > 1) {
if (STREQ(argv[1], "--help"))
usage(EXIT_SUCCESS);
if (STREQ(argv[1], "--version")) {
helperVersion(argv[0]);
exit(EXIT_SUCCESS);
}
}
if (argc != 4 && argc != 5 && argc != 2) {
/* Refer man page of dnsmasq --dhcp-script for more details */
usage(EXIT_FAILURE);
}
/* Make sure dnsmasq knows the interface. The interface name is not known
* via env variable set by dnsmasq when dnsmasq (re)starts and throws 'del'
* events for expired leases. So, libvirtd sets another env var for this
* purpose */
if (!interface &&
!(interface = getenv("VIR_BRIDGE_NAME")))
goto cleanup;
ip = argv[3];
mac = argv[2];
if ((action = virLeaseActionTypeFromString(argv[1])) < 0) {
fprintf(stderr, _("Unsupported action: %s\n"), argv[1]);
exit(EXIT_FAILURE);
}
/* In case hostname is known, it is the 5th argument */
if (argc == 5)
hostname = argv[4];
/* Check if it is an IPv6 lease */
if (iaid) {
mac = getenv("DNSMASQ_MAC");
clientid = argv[2];
}
server_duid = g_strdup(getenv("DNSMASQ_SERVER_DUID"));
custom_lease_file = g_strdup_printf(LOCALSTATEDIR "/lib/libvirt/dnsmasq/%s.status",
interface);
pid_file = g_strdup(RUNSTATEDIR "/leaseshelper.pid");
/* Try to claim the pidfile, exiting if we can't */
if ((pid_file_fd = virPidFileAcquirePath(pid_file, true, getpid())) < 0)
goto cleanup;
/* Since interfaces can be hot plugged, we need to make sure that the
* corresponding custom lease file exists. If not, 'touch' it */
if (virFileTouch(custom_lease_file, 0644) < 0)
goto cleanup;
switch ((enum virLeaseActionFlags) action) {
case VIR_LEASE_ACTION_ADD:
case VIR_LEASE_ACTION_OLD:
/* Create new lease */
if (virLeaseNew(&lease_new, mac, clientid, ip, hostname, iaid, server_duid) < 0)
goto cleanup;
/* Custom ipv6 leases *will not* be created if the env-var DNSMASQ_MAC
* is not set. In the special case, when the $(interface).status file
* is not already present and dnsmasq is (re)started, the corresponding
* ipv6 custom lease will be created only when the guest sends the
* 'old' action for its existing ipv6 interfaces.
*
* According to rfc3315, the combination of DUID and IAID can be used
* to uniquely identify each ipv6 guest interface. So, in future, if
* we introduce virNetworkGetDHCPLeaseBy(IAID|DUID|IAID+DUID) for ipv6
* interfaces, then, the following if condition won't be required, as
* the new lease will be created irrespective of whether the MACID is
* known or not.
*/
if (!lease_new)
break;
G_GNUC_FALLTHROUGH;
case VIR_LEASE_ACTION_DEL:
/* Delete the corresponding lease, if it already exists */
delete = true;
break;
case VIR_LEASE_ACTION_INIT:
case VIR_LEASE_ACTION_LAST:
break;
}
leases_array_new = virJSONValueNewArray();
if (virLeaseReadCustomLeaseFile(leases_array_new, custom_lease_file,
delete ? ip : NULL, &server_duid) < 0)
goto cleanup;
switch ((enum virLeaseActionFlags) action) {
case VIR_LEASE_ACTION_INIT:
if (virLeasePrintLeases(leases_array_new, server_duid) < 0)
goto cleanup;
break;
case VIR_LEASE_ACTION_OLD:
case VIR_LEASE_ACTION_ADD:
if (lease_new && virJSONValueArrayAppend(leases_array_new, lease_new) < 0) {
virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
_("failed to create json"));
goto cleanup;
}
lease_new = NULL;
G_GNUC_FALLTHROUGH;
case VIR_LEASE_ACTION_DEL:
if (!(leases_str = virJSONValueToString(leases_array_new, true))) {
virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
_("empty json array"));
goto cleanup;
}
/* Write to file */
if (virFileRewriteStr(custom_lease_file, 0644, leases_str) < 0)
goto cleanup;
break;
case VIR_LEASE_ACTION_LAST:
break;
}
rv = EXIT_SUCCESS;
cleanup:
if (pid_file_fd != -1)
virPidFileReleasePath(pid_file, pid_file_fd);
VIR_FREE(pid_file);
VIR_FREE(server_duid);
VIR_FREE(custom_lease_file);
virJSONValueFree(lease_new);
virJSONValueFree(leases_array_new);
return rv;
}