Re: [libvirt] [PATCH] network: add an option to make dns public

On 06/10/2015 03:56 PM, John Ferlan wrote: > > On 06/01/2015 07:54 AM, Cédric Bosdonnat wrote: >> In some use cases we don't want the virtual network's DNS to only >> listen to the vnet interface. Adding a publiclyAccessible attribute :-) Really, that name was only intended as a placeholder! I was hoping you (or someone else) would be able to find something shorter/simpler. Lacking that, I guess this is a reasonable name though.

>> to the dns element in the configuration allows the DNS to listen to >> all interfaces. >> >> It simply disables the bind-dynamic option of dnsmasq for the network. >> --- >> docs/formatnetwork.html.in | 11 +++++++++++ >> docs/schemas/network.rng | 15 ++++++++++----- >> src/conf/network_conf.c | 6 ++++++ >> src/conf/network_conf.h | 1 + >> src/network/bridge_driver.c | 4 +++- >> tests/networkxml2confdata/nat-network-dns-hosts.conf | 1 - >> tests/networkxml2confdata/nat-network-dns-hosts.xml | 2 +- >> 7 files changed, 32 insertions(+), 8 deletions(-) >> >> diff --git a/docs/formatnetwork.html.in b/docs/formatnetwork.html.in >> index 6abed8f..8e43658 100644 >> --- a/docs/formatnetwork.html.in >> +++ b/docs/formatnetwork.html.in >> @@ -851,6 +851,17 @@ >> DNS server. >> </p> >> >> + <p> >> + The dns element >> + can have an optional <code>publiclyAccessible</code> >> + attribute <span class="since">Since 1.2.17</span>. >> + If <code>publiclyAccessible</code> is "yes", then the DNS server >> + will handle requests for all interfaces. >> + If <code>publiclyAccessible</code> is not set or "no", the DNS >> + server will only handle requests for the interface of the virtual >> + network. >> + </p> >> + >> Currently supported sub-elements of <code>&lt;dns&gt;</code> are: >> <dl> >> <dt><code>forwarder</code></dt> >> diff --git a/docs/schemas/network.rng b/docs/schemas/network.rng >> index 4edb6eb..f989625 100644 >> --- a/docs/schemas/network.rng >> +++ b/docs/schemas/network.rng >> @@ -244,12 +244,17 @@ >> and other features in the <dns> element --> >> <optional> >> <element name="dns"> >> - <optional> >> - <attribute name="forwardPlainNames"> >> - <ref name="virYesNo"/> >> - </attribute> >> - </optional> >> <interleave> >> + <optional> >> + <attribute name="forwardPlainNames"> >> + <ref name="virYesNo"/> >> + </attribute> >> + </optional> >> + <optional> >> + <attribute name="publiclyAccessible"> >> + <ref name="virYesNo"/> >> + </attribute> >> + </optional> > Moving the attributes inside the <interleave> had me looking through > other .rng's... I'm no expert, but had thought they really only mattered > for <element>'s I'm not an expert either, but you are correct :-)

>> <zeroOrMore> >> <element name="forwarder"> >> <attribute name="addr"><ref name="ipAddr"/></attribute> >> diff --git a/src/conf/network_conf.c b/src/conf/network_conf.c >> index f4a9df0..99bac6d 100644 >> --- a/src/conf/network_conf.c >> +++ b/src/conf/network_conf.c >> @@ -1309,9 +1309,14 @@ virNetworkDNSDefParseXML(const char *networkName, >> size_t i; >> int ret = -1; >> xmlNodePtr save = ctxt->node; >> + char *publiclyAccessible = NULL; >> >> ctxt->node = node; >> >> + publiclyAccessible = virXPathString("string(./@publiclyAccessible)", ctxt); >> + if (publiclyAccessible) >> + def->publiclyAccessible = virTristateBoolTypeFromString(publiclyAccessible); >> + >> forwardPlainNames = virXPathString("string(./@forwardPlainNames)", ctxt); >> if (forwardPlainNames) { >> def->forwardPlainNames = virTristateBoolTypeFromString(forwardPlainNames); >> @@ -1410,6 +1415,7 @@ virNetworkDNSDefParseXML(const char *networkName, >> >> ret = 0; >> cleanup: >> + VIR_FREE(publiclyAccessible); >> VIR_FREE(forwardPlainNames); >> VIR_FREE(fwdNodes); >> VIR_FREE(hostNodes); >> diff --git a/src/conf/network_conf.h b/src/conf/network_conf.h >> index f69d999..f555b6b 100644 >> --- a/src/conf/network_conf.h >> +++ b/src/conf/network_conf.h >> @@ -136,6 +136,7 @@ struct _virNetworkDNSDef { >> virNetworkDNSSrvDefPtr srvs; >> size_t nfwds; >> char **forwarders; >> + int publiclyAccessible; /* enum virTristateBool */ >> }; >> >> typedef struct _virNetworkIpDef virNetworkIpDef; >> diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c >> index d195085..c39b1a5 100644 >> --- a/src/network/bridge_driver.c >> +++ b/src/network/bridge_driver.c >> @@ -996,8 +996,10 @@ networkDnsmasqConfContents(virNetworkObjPtr network, >> * other than one of the virtual guests connected directly to >> * this network). This was added in response to CVE 2012-3411. >> */ >> + if (network->def->dns.publiclyAccessible != VIR_TRISTATE_BOOL_YES) >> + virBufferAddLit(&configbuf, >> + "bind-dynamic\n"); >> virBufferAsprintf(&configbuf, >> - "bind-dynamic\n" >> "interface=%s\n", >> network->def->bridge); >> } else { >> diff --git a/tests/networkxml2confdata/nat-network-dns-hosts.conf b/tests/networkxml2confdata/nat-network-dns-hosts.conf >> index 021316f..759a9e9 100644 >> --- a/tests/networkxml2confdata/nat-network-dns-hosts.conf >> +++ b/tests/networkxml2confdata/nat-network-dns-hosts.conf >> @@ -10,6 +10,5 @@ expand-hosts >> domain-needed >> local=// >> except-interface=lo >> -bind-dynamic >> interface=virbr0 >> addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts >> diff --git a/tests/networkxml2confdata/nat-network-dns-hosts.xml b/tests/networkxml2confdata/nat-network-dns-hosts.xml >> index 9add456..969dfa5 100644 >> --- a/tests/networkxml2confdata/nat-network-dns-hosts.xml >> +++ b/tests/networkxml2confdata/nat-network-dns-hosts.xml >> @@ -4,7 +4,7 @@ >> <forward dev='eth0' mode='nat'/> >> <bridge name='virbr0' stp='on' delay='0'/> >> <domain name="example.com"/> >> - <dns forwardPlainNames='no'> >> + <dns forwardPlainNames='no' publiclyAccessible='yes'> >> <host ip='192.168.122.1'> >> <hostname>host</hostname> >> <hostname>gateway</hostname> >> > Rather than change an existing test, a new test or two should be > created... One that specifically states 'yes' and possibly one that has > 'no' keeping the existing one with nothing provided to be sure that > works as well.

> I don't mind doing that for you, but also I figure by bumping this > perhaps Laine will take a look too since he usually responds to most of > the network related patches anyway... It seems fine to me though. This is better than the previously proposed "bindDynamic" option (or whatever it was called; I just remember it was something dnsmasq-specific). However, the patch doesn't put "bind-interfaces" in place of "bind-dynamic", and unless I'm remembering incorrectly, removing bind-dynamic without adding "bind-interfaces" will cause multiple dnsmasq instances to conflict with each other - when neither option is used, dnsmasq will create a single socket listening on the wildcard address, then discard packets not intended for the IP address/interface; if any application listens on a given port using the wildcard address, no other application will be able to listen on that port on *any* interface/address. Here's an email that describes the differences: http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2012q4/006525.html Beyond that, I don't think that the name/description of this new option ("publiclyAccessible") really fits the original problem that I believe prompted the creation of the patch. As I understand it, the original problem was that LXC guests connected to a libvirt network were unable to get their IP address via dhcp (and probably weren't able to use libvirt's DNS server) because the packets were identified as arriving on the host side of the guest's veth interface rather than on the libvirt network's bridge device (the previous patch for this said something about vlans - was it only a problem in the case of vlans?).

I don't have a problem pushing this patch (after modifying it to use bind-interfaces when bind-dynamic isn't used, adding some new unit tests as John described, and copious amounts of regression testing, e.g. multiple simultaneous networks with a mixture of publiclyAccessible='yes|no', running a systemwide instance of dnsmasq with bind-dynamic//bind-interfaces at the same time, routed and nated networks, qemu and lxc guests with/without dhcp, etc).

But I think that we should still try to find a solution to the original problem that doesn't involve opening up the DNS and DHCP servers to receiving packets that arrived on *any* interface. (Cedric - perhaps you could provide a config for something that doesn't work so that I can be sure I'm understanding exactly what is the problem).