From 2abde0ac0740e57c47ed684ce0d56195b977bdb3 Mon Sep 17 00:00:00 2001 From: Laine Stump Date: Wed, 21 Nov 2012 21:21:02 -0500 Subject: [PATCH] network: use dnsmasq --bind-dynamic when available This bug resolves CVE-2012-3411, which is described in the following bugzilla report: https://bugzilla.redhat.com/show_bug.cgi?id=833033 The following report is specifically for libvirt on Fedora: https://bugzilla.redhat.com/show_bug.cgi?id=874702 In short, a dnsmasq instance run with the intention of listening for DHCP/DNS requests only on a libvirt virtual network (which is constructed using a Linux host bridge) would also answer queries sent from outside the virtualization host. This patch takes advantage of a new dnsmasq option "--bind-dynamic", which will cause the listening socket to be setup such that it will only receive those requests that actually come in via the bridge interface. In order for this behavior to actually occur, not only must "--bind-interfaces" be replaced with "--bind-dynamic", but also all "--listen-address" options must be replaced with a single "--interface" option. Fully: --bind-interfaces --except-interface lo --listen-address x.x.x.x ... (with --listen-address possibly repeated) is replaced with: --bind-dynamic --interface virbrX Of course libvirt can't use this new option if the host's dnsmasq doesn't have it, but we still want libvirt to function (because the great majority of libvirt installations, which only have mode='nat' networks using RFC1918 private address ranges (e.g. 192.168.122.0/24), are immune to this vulnerability from anywhere beyond the local subnet of the host), so we use the new dnsmasqCaps API to check if dnsmasq supports the new option and, if not, we use the "old" option style instead. In order to assure that this permissiveness doesn't lead to a vulnerable system, we do check for non-private addresses in this case, and refuse to start the network if both a) we are using the old-style options, and b) the network has a publicly routable IP address. Hopefully this will provide the proper balance of not being disruptive to those not practically affected, and making sure that those who *are* affected get their dnsmasq upgraded. (--bind-dynamic was added to dnsmasq in upstream commit 54dd393f3938fc0c19088fbd319b95e37d81a2b0, which was included in dnsmasq-2.63) (cherry picked from commit 753ff83a50263d6975f88d6605d4b5ddfcc97560) Conflicts: src/network/bridge_driver.c * needed to change virReportError() to the older networkReportError() tests/networkxml2argvdata/nat-network-dns-txt-record.argv * this test file has an example of an arg with embedded space, which gets sorrounded by '' in newer releases. Other items on the same line had been modified. tests/networkxml2argvdata/routed-network.argv * in the newer releases, this test file had an --addn-hosts arg that didn't exist on this branch. Again, it was in the surrounding context of the changes that had been made on master. --- src/network/bridge_driver.c | 81 ++++++++++++++----- .../networkxml2argvdata/isolated-network.argv | 5 +- .../nat-network-dns-hosts.argv | 5 +- .../nat-network-dns-srv-record-minimal.argv | 9 +-- .../nat-network-dns-srv-record-minimal.xml | 4 +- .../nat-network-dns-srv-record.argv | 8 +- .../nat-network-dns-txt-record.argv | 8 +- tests/networkxml2argvdata/nat-network.argv | 6 +- .../networkxml2argvdata/netboot-network.argv | 4 +- .../netboot-proxy-network.argv | 5 +- tests/networkxml2argvdata/routed-network.argv | 4 +- 11 files changed, 84 insertions(+), 55 deletions(-) diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c index b9332281e2..8010797d6c 100644 --- a/src/network/bridge_driver.c +++ b/src/network/bridge_driver.c @@ -495,7 +495,7 @@ networkBuildDnsmasqArgv(virNetworkObjPtr network, * Needed to ensure dnsmasq uses same algorithm for processing * multiple namedriver entries in /etc/resolv.conf as GLibC. */ - virCommandAddArgList(cmd, "--strict-order", "--bind-interfaces", NULL); + virCommandAddArg(cmd, "--strict-order"); if (network->def->domain) virCommandAddArgPair(cmd, "--domain", network->def->domain); @@ -510,9 +510,64 @@ networkBuildDnsmasqArgv(virNetworkObjPtr network, /* *no* conf file */ virCommandAddArg(cmd, "--conf-file="); - virCommandAddArgList(cmd, - "--except-interface", "lo", - NULL); + if (dnsmasqCapsGet(caps, DNSMASQ_CAPS_BIND_DYNAMIC)) { + /* using --bind-dynamic with only --interface (no + * --listen-address) prevents dnsmasq from responding to dns + * queries that arrive on some interface other than our bridge + * interface (in other words, requests originating somewhere + * other than one of the virtual guests connected directly to + * this network). This was added in response to CVE 2012-3411. + */ + virCommandAddArgList(cmd, + "--bind-dynamic", + "--interface", network->def->bridge, + NULL); + } else { + virCommandAddArgList(cmd, + "--bind-interfaces", + "--except-interface", "lo", + NULL); + /* + * --interface does not actually work with dnsmasq < 2.47, + * due to DAD for ipv6 addresses on the interface. + * + * virCommandAddArgList(cmd, "--interface", network->def->bridge, NULL); + * + * So listen on all defined IPv[46] addresses + */ + for (ii = 0; + (tmpipdef = virNetworkDefGetIpByIndex(network->def, AF_UNSPEC, ii)); + ii++) { + char *ipaddr = virSocketAddrFormat(&tmpipdef->address); + + if (!ipaddr) + goto cleanup; + /* also part of CVE 2012-3411 - if the host's version of + * dnsmasq doesn't have --bind-dynamic, only allow listening on + * private/local IP addresses (see RFC1918/RFC3484/RFC4193) + */ + if (!virSocketAddrIsPrivate(&tmpipdef->address)) { + unsigned long version = dnsmasqCapsGetVersion(caps); + + networkReportError(VIR_ERR_CONFIG_UNSUPPORTED, + _("Publicly routable address %s is " + "prohibited. The version of dnsmasq on " + "this host (%d.%d) doesn't support the " + "--bind-dynamic option, which is required " + "for safe operation on a publicly " + "routable subnet (see CVE-2012-3411). " + "You must either upgrade dnsmasq, or use " + "a private/local subnet range for this " + "network (as described " + "in RFC1918/RFC3484/RFC4193)."), ipaddr, + (int)version / 1000000, + (int)(version % 1000000) / 1000); + goto cleanup; + } + virCommandAddArgList(cmd, "--listen-address", ipaddr, NULL); + VIR_FREE(ipaddr); + } + } /* If this is an isolated network, set the default route option * (3) to be empty to avoid setting a default route that's @@ -578,24 +633,6 @@ networkBuildDnsmasqArgv(virNetworkObjPtr network, } } - /* - * --interface does not actually work with dnsmasq < 2.47, - * due to DAD for ipv6 addresses on the interface. - * - * virCommandAddArgList(cmd, "--interface", ipdef->bridge, NULL); - * - * So listen on all defined IPv[46] addresses - */ - for (ii = 0; - (tmpipdef = virNetworkDefGetIpByIndex(network->def, AF_UNSPEC, ii)); - ii++) { - char *ipaddr = virSocketAddrFormat(&tmpipdef->address); - if (!ipaddr) - goto cleanup; - virCommandAddArgList(cmd, "--listen-address", ipaddr, NULL); - VIR_FREE(ipaddr); - } - if (ipdef) { for (r = 0 ; r < ipdef->nranges ; r++) { char *saddr = virSocketAddrFormat(&ipdef->ranges[r].start); diff --git a/tests/networkxml2argvdata/isolated-network.argv b/tests/networkxml2argvdata/isolated-network.argv index 048c72b287..d629192e88 100644 --- a/tests/networkxml2argvdata/isolated-network.argv +++ b/tests/networkxml2argvdata/isolated-network.argv @@ -1,7 +1,8 @@ -@DNSMASQ@ --strict-order --bind-interfaces \ +@DNSMASQ@ --strict-order \ --local=// --domain-needed --conf-file= \ ---except-interface lo --dhcp-option=3 --no-resolv \ +--bind-interfaces --except-interface lo \ --listen-address 192.168.152.1 \ +--dhcp-option=3 --no-resolv \ --dhcp-range 192.168.152.2,192.168.152.254 \ --dhcp-leasefile=/var/lib/libvirt/dnsmasq/private.leases --dhcp-lease-max=253 \ --dhcp-no-override\ diff --git a/tests/networkxml2argvdata/nat-network-dns-hosts.argv b/tests/networkxml2argvdata/nat-network-dns-hosts.argv index 03a0676935..e5143acbbe 100644 --- a/tests/networkxml2argvdata/nat-network-dns-hosts.argv +++ b/tests/networkxml2argvdata/nat-network-dns-hosts.argv @@ -1,4 +1,5 @@ -@DNSMASQ@ --strict-order --bind-interfaces --domain=example.com \ +@DNSMASQ@ --strict-order --domain=example.com \ --local=/example.com/ --domain-needed \ ---conf-file= --except-interface lo --listen-address 192.168.122.1 \ +--conf-file= \ +--bind-dynamic --interface virbr0 \ --expand-hosts --addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts\ diff --git a/tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.argv b/tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.argv index a1e420055e..c38b954979 100644 --- a/tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.argv +++ b/tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.argv @@ -1,14 +1,13 @@ @DNSMASQ@ \ --strict-order \ ---bind-interfaces \ --local=// --domain-needed --conf-file= \ ---except-interface lo \ ---srv-host=name.tcp.,,,, \ +--bind-interfaces --except-interface lo \ --listen-address 192.168.122.1 \ --listen-address 192.168.123.1 \ ---listen-address 2001:db8:ac10:fe01::1 \ ---listen-address 2001:db8:ac10:fd01::1 \ +--listen-address fc00:db8:ac10:fe01::1 \ +--listen-address fc00:db8:ac10:fd01::1 \ --listen-address 10.24.10.1 \ +--srv-host=name.tcp.,,,, \ --dhcp-range 192.168.122.2,192.168.122.254 \ --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \ --dhcp-lease-max=253 \ diff --git a/tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.xml b/tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.xml index e9b7680603..f6f24e1208 100644 --- a/tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.xml +++ b/tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.xml @@ -17,9 +17,9 @@ - + - + diff --git a/tests/networkxml2argvdata/nat-network-dns-srv-record.argv b/tests/networkxml2argvdata/nat-network-dns-srv-record.argv index 8af38c416f..311b0d76f9 100644 --- a/tests/networkxml2argvdata/nat-network-dns-srv-record.argv +++ b/tests/networkxml2argvdata/nat-network-dns-srv-record.argv @@ -1,14 +1,8 @@ @DNSMASQ@ \ --strict-order \ ---bind-interfaces \ --local=// --domain-needed --conf-file= \ ---except-interface lo \ +--bind-dynamic --interface virbr0 \ --srv-host=name.tcp.test-domain-name,.,1024,10,10 \ ---listen-address 192.168.122.1 \ ---listen-address 192.168.123.1 \ ---listen-address 2001:db8:ac10:fe01::1 \ ---listen-address 2001:db8:ac10:fd01::1 \ ---listen-address 10.24.10.1 \ --dhcp-range 192.168.122.2,192.168.122.254 \ --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \ --dhcp-lease-max=253 \ diff --git a/tests/networkxml2argvdata/nat-network-dns-txt-record.argv b/tests/networkxml2argvdata/nat-network-dns-txt-record.argv index 80a2fce385..cbdf50db9a 100644 --- a/tests/networkxml2argvdata/nat-network-dns-txt-record.argv +++ b/tests/networkxml2argvdata/nat-network-dns-txt-record.argv @@ -1,9 +1,7 @@ -@DNSMASQ@ --strict-order --bind-interfaces \ +@DNSMASQ@ --strict-order \ --local=// --domain-needed --conf-file= \ ---except-interface lo --txt-record=example,example value \ ---listen-address 192.168.122.1 --listen-address 192.168.123.1 \ ---listen-address 2001:db8:ac10:fe01::1 \ ---listen-address 2001:db8:ac10:fd01::1 --listen-address 10.24.10.1 \ +--bind-dynamic --interface virbr0 \ +--txt-record=example,example value \ --dhcp-range 192.168.122.2,192.168.122.254 \ --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \ --dhcp-lease-max=253 --dhcp-no-override \ diff --git a/tests/networkxml2argvdata/nat-network.argv b/tests/networkxml2argvdata/nat-network.argv index 1dc8f73d16..967ca94591 100644 --- a/tests/networkxml2argvdata/nat-network.argv +++ b/tests/networkxml2argvdata/nat-network.argv @@ -1,8 +1,6 @@ -@DNSMASQ@ --strict-order --bind-interfaces \ +@DNSMASQ@ --strict-order \ --local=// --domain-needed --conf-file= \ ---except-interface lo --listen-address 192.168.122.1 \ ---listen-address 192.168.123.1 --listen-address 2001:db8:ac10:fe01::1 \ ---listen-address 2001:db8:ac10:fd01::1 --listen-address 10.24.10.1 \ +--bind-dynamic --interface virbr0 \ --dhcp-range 192.168.122.2,192.168.122.254 \ --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \ --dhcp-lease-max=253 --dhcp-no-override \ diff --git a/tests/networkxml2argvdata/netboot-network.argv b/tests/networkxml2argvdata/netboot-network.argv index 5a85ec2e7a..bcd6fad5d1 100644 --- a/tests/networkxml2argvdata/netboot-network.argv +++ b/tests/networkxml2argvdata/netboot-network.argv @@ -1,6 +1,6 @@ -@DNSMASQ@ --strict-order --bind-interfaces --domain=example.com \ +@DNSMASQ@ --strict-order --domain=example.com \ --local=/example.com/ --domain-needed --conf-file= \ ---except-interface lo --listen-address 192.168.122.1 \ +--bind-interfaces --except-interface lo --listen-address 192.168.122.1 \ --dhcp-range 192.168.122.2,192.168.122.254 \ --dhcp-leasefile=/var/lib/libvirt/dnsmasq/netboot.leases \ --dhcp-lease-max=253 --dhcp-no-override --expand-hosts --enable-tftp \ diff --git a/tests/networkxml2argvdata/netboot-proxy-network.argv b/tests/networkxml2argvdata/netboot-proxy-network.argv index 36836b09d3..8c5ef9bf44 100644 --- a/tests/networkxml2argvdata/netboot-proxy-network.argv +++ b/tests/networkxml2argvdata/netboot-proxy-network.argv @@ -1,6 +1,7 @@ -@DNSMASQ@ --strict-order --bind-interfaces --domain=example.com \ +@DNSMASQ@ --strict-order --domain=example.com \ --local=/example.com/ --domain-needed --conf-file= \ ---except-interface lo --listen-address 192.168.122.1 \ +--bind-interfaces --except-interface lo \ +--listen-address 192.168.122.1 \ --dhcp-range 192.168.122.2,192.168.122.254 \ --dhcp-leasefile=/var/lib/libvirt/dnsmasq/netboot.leases \ --dhcp-lease-max=253 --dhcp-no-override --expand-hosts \ diff --git a/tests/networkxml2argvdata/routed-network.argv b/tests/networkxml2argvdata/routed-network.argv index 77e802f843..eacdf2d70a 100644 --- a/tests/networkxml2argvdata/routed-network.argv +++ b/tests/networkxml2argvdata/routed-network.argv @@ -1,3 +1,3 @@ -@DNSMASQ@ --strict-order --bind-interfaces \ +@DNSMASQ@ --strict-order \ --local=// --domain-needed --conf-file= \ ---except-interface lo --listen-address 192.168.122.1\ +--bind-dynamic --interface virbr1\