Il 18/04/2013 19:32, Laine Stump ha scritto:
On 03/25/2013 10:25 AM, Paolo Bonzini wrote:
<source type='bridge'> uses a helper application to do the necessary TUN/TAP setup to use an existing network bridge, thus letting unprivileged users use TUN/TAP interfaces.
However, libvirt should be preventing QEMU from running any setuid programs at all, which would include this helper program. From a security POV, any setuid helper needs to be run by libvirtd itself, not QEMU.
This is what this patch does. libvirt now invokes the setuid helper, gets the TAP fd and then passes it to QEMU in the normal manner. The path to the helper is specified in qemu.conf.
As a small advantage, this adds a <target dev='tap0'/> element to the XML of an active domain using <interface type='bridge'>.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- src/qemu/qemu_command.c | 133 +++++++++++++++++++++++++++++++++++------------- src/qemu/qemu_command.h | 1 - src/qemu/qemu_hotplug.c | 25 +++------ 3 files changed, 106 insertions(+), 53 deletions(-)
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index a0c278f..fa31102 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -28,12 +28,14 @@ #include "qemu_capabilities.h" #include "qemu_bridge_filter.h" #include "cpu/cpu.h" +#include "passfd.h" #include "viralloc.h" #include "virlog.h" #include "virarch.h" #include "virerror.h" #include "virutil.h" #include "virfile.h" +#include "virnetdev.h" #include "virstring.h" #include "viruuid.h" #include "c-ctype.h" @@ -46,6 +48,9 @@ #include "base64.h" #include "device_conf.h" #include "virstoragefile.h" +#if defined(__linux__) +# include <linux/capability.h> +#endif
#include <sys/stat.h> #include <fcntl.h> @@ -193,6 +198,77 @@ error: }
+/** + * qemuCreateInBridgePortWithHelper: + * @cfg: the configuration object in which the helper name is looked up + * @brname: the bridge name + * @ifname: the returned interface name + * @macaddr: the returned MAC address + * @tapfd: file descriptor return value for the new tap device + * @flags: OR of virNetDevTapCreateFlags: + + * VIR_NETDEV_TAP_CREATE_VNET_HDR + * - Enable IFF_VNET_HDR on the tap device + * + * This function creates a new tap device on a bridge using an external + * helper. The final name for the bridge will be stored in @ifname. + * + * Returns 0 in case of success or -1 on failure + */ +static int qemuCreateInBridgePortWithHelper(virQEMUDriverConfigPtr cfg, + const char *brname, + char **ifname, + int *tapfd, + unsigned int flags) +{ + virCommandPtr cmd; + int status; + int pair[2] = { -1, -1 }; + + if ((flags & ~VIR_NETDEV_TAP_CREATE_VNET_HDR) != VIR_NETDEV_TAP_CREATE_IFUP) + return -1; + + if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) < 0) { + virReportSystemError(errno, "%s", _("failed to create socket")); + return -1; + } + + cmd = virCommandNew(cfg->bridgeHelperName); + if (flags & VIR_NETDEV_TAP_CREATE_VNET_HDR) + virCommandAddArgFormat(cmd, "--use-vnet"); + virCommandAddArgFormat(cmd, "--br=%s", brname); + virCommandAddArgFormat(cmd, "--fd=%d", pair[1]); + virCommandTransferFD(cmd, pair[1]); + virCommandClearCaps(cmd); +#ifdef CAP_NET_ADMIN + virCommandAllowCap(cmd, CAP_NET_ADMIN);
I thought you had said that attempts to set caps would fail because CAP_SETPCAP was cleared for the non-privileged libvirtd.
I still prefer to note down the capabilities. This way running libvirt with CAP_SETPCAP as a permitted file capability (and only that one + the effective bit set) should do the right thing. I tested this by forcing this path for the system libvirt.
+#endif + if (virCommandRunAsync(cmd, NULL) < 0) { + *tapfd = -1; + goto out; + } + + do { + *tapfd = recvfd(pair[0], 0); + } while (*tapfd < 0 && errno == EINTR); + if (*tapfd < 0) { + virReportSystemError(errno, "%s", + _("failed to retrieve file descriptor for interface")); + goto out; + } + + if (virNetDevTapGetName(*tapfd, ifname) < 0 || + virCommandWait(cmd, &status) < 0) { + VIR_FORCE_CLOSE(*tapfd); + *tapfd = -1; + } + +out:
We prefer to name these labels "cleanup" rather that "out" (although there are some occurrences of "out" still in the code).
Ok. Paolo
+ virCommandFree(cmd); + VIR_FORCE_CLOSE(pair[0]); + return *tapfd < 0 ? -1 : 0; +} + int qemuNetworkIfaceConnect(virDomainDefPtr def, virConnectPtr conn, @@ -270,11 +346,17 @@ qemuNetworkIfaceConnect(virDomainDefPtr def, tap_create_flags |= VIR_NETDEV_TAP_CREATE_VNET_HDR; }
- err = virNetDevTapCreateInBridgePort(brname, &net->ifname, &net->mac, - def->uuid, &tapfd, - virDomainNetGetActualVirtPortProfile(net), - virDomainNetGetActualVlan(net), - tap_create_flags); + if (cfg->privileged) + err = virNetDevTapCreateInBridgePort(brname, &net->ifname, &net->mac, + def->uuid, &tapfd, + virDomainNetGetActualVirtPortProfile(net), + virDomainNetGetActualVlan(net), + tap_create_flags); + else + err = qemuCreateInBridgePortWithHelper(cfg, brname, + &net->ifname, + &tapfd, tap_create_flags); + virDomainAuditNetDevice(def, net, "/dev/net/tun", tapfd >= 0); if (err < 0) { if (template_ifname) @@ -3746,7 +3828,6 @@ error: char * qemuBuildHostNetStr(virDomainNetDefPtr net, virQEMUDriverPtr driver, - virQEMUCapsPtr qemuCaps,
qemuCaps might again become useful for this function in the future, so you may want to leave it here (marked as ATTRIBUTE_UNUSED) to reduce code churn.
char type_sep, int vlan, const char *tapfd, @@ -3755,7 +3836,6 @@ qemuBuildHostNetStr(virDomainNetDefPtr net, bool is_tap = false; virBuffer buf = VIR_BUFFER_INITIALIZER; enum virDomainNetType netType = virDomainNetGetActualType(net); - const char *brname = NULL; virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
if (net->script && netType != VIR_DOMAIN_NET_TYPE_ETHERNET) { @@ -3773,14 +3853,6 @@ qemuBuildHostNetStr(virDomainNetDefPtr net, * through, -net tap,fd */ case VIR_DOMAIN_NET_TYPE_BRIDGE: - if (!cfg->privileged && - virQEMUCapsGet(qemuCaps, QEMU_CAPS_NETDEV_BRIDGE)) { - brname = virDomainNetGetActualBridgeName(net); - virBufferAsprintf(&buf, "bridge%cbr=%s", type_sep, brname); - type_sep = ','; - is_tap = true; - break; - } case VIR_DOMAIN_NET_TYPE_NETWORK: case VIR_DOMAIN_NET_TYPE_DIRECT: virBufferAsprintf(&buf, "tap%cfd=%s", type_sep, tapfd); @@ -6681,26 +6753,17 @@ qemuBuildCommandLine(virConnectPtr conn,
if (actualType == VIR_DOMAIN_NET_TYPE_NETWORK || actualType == VIR_DOMAIN_NET_TYPE_BRIDGE) { - /* - * If type='bridge' then we attempt to allocate the tap fd here only if - * running under a privilged user or -netdev bridge option is not - * supported. - */ - if (actualType == VIR_DOMAIN_NET_TYPE_NETWORK || - cfg->privileged || - (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_NETDEV_BRIDGE))) { - int tapfd = qemuNetworkIfaceConnect(def, conn, driver, net, - qemuCaps); - if (tapfd < 0) - goto error; + int tapfd = qemuNetworkIfaceConnect(def, conn, driver, net, + qemuCaps); + if (tapfd < 0) + goto error;
- last_good_net = i; - virCommandTransferFD(cmd, tapfd); + last_good_net = i; + virCommandTransferFD(cmd, tapfd);
- if (snprintf(tapfd_name, sizeof(tapfd_name), "%d", - tapfd) >= sizeof(tapfd_name)) - goto no_memory; - } + if (snprintf(tapfd_name, sizeof(tapfd_name), "%d", + tapfd) >= sizeof(tapfd_name)) + goto no_memory; } else if (actualType == VIR_DOMAIN_NET_TYPE_DIRECT) { int tapfd = qemuPhysIfaceConnect(def, driver, net, qemuCaps, vmop); @@ -6744,7 +6807,7 @@ qemuBuildCommandLine(virConnectPtr conn, if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_NETDEV) && virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE)) { virCommandAddArg(cmd, "-netdev"); - if (!(host = qemuBuildHostNetStr(net, driver, qemuCaps, + if (!(host = qemuBuildHostNetStr(net, driver, ',', vlan, tapfd_name, vhostfd_name))) goto error; @@ -6768,7 +6831,7 @@ qemuBuildCommandLine(virConnectPtr conn, if (!(virQEMUCapsGet(qemuCaps, QEMU_CAPS_NETDEV) && virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE))) { virCommandAddArg(cmd, "-net"); - if (!(host = qemuBuildHostNetStr(net, driver, qemuCaps, + if (!(host = qemuBuildHostNetStr(net, driver, ',', vlan, tapfd_name, vhostfd_name))) goto error; diff --git a/src/qemu/qemu_command.h b/src/qemu/qemu_command.h index 17687f4..267a96e 100644 --- a/src/qemu/qemu_command.h +++ b/src/qemu/qemu_command.h @@ -71,7 +71,6 @@ qemuBuildChrDeviceStr (virDomainChrDefPtr serial, /* With vlan == -1, use netdev syntax, else old hostnet */ char * qemuBuildHostNetStr(virDomainNetDefPtr net, virQEMUDriverPtr driver, - virQEMUCapsPtr qemuCaps, char type_sep, int vlan, const char *tapfd, diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index de9edd4..6891efd 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -729,21 +729,12 @@ int qemuDomainAttachNetDevice(virConnectPtr conn,
if (actualType == VIR_DOMAIN_NET_TYPE_BRIDGE || actualType == VIR_DOMAIN_NET_TYPE_NETWORK) { - /* - * If type=bridge then we attempt to allocate the tap fd here only if - * running under a privilged user or -netdev bridge option is not - * supported. - */ - if (actualType == VIR_DOMAIN_NET_TYPE_NETWORK || - cfg->privileged || - (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_NETDEV_BRIDGE))) { - if ((tapfd = qemuNetworkIfaceConnect(vm->def, conn, driver, net, - priv->qemuCaps)) < 0) - goto cleanup; - iface_connected = true; - if (qemuOpenVhostNet(vm->def, net, priv->qemuCaps, &vhostfd) < 0) - goto cleanup; - } + if ((tapfd = qemuNetworkIfaceConnect(vm->def, conn, driver, net, + priv->qemuCaps)) < 0) + goto cleanup; + iface_connected = true; + if (qemuOpenVhostNet(vm->def, net, priv->qemuCaps, &vhostfd) < 0) + goto cleanup; } else if (actualType == VIR_DOMAIN_NET_TYPE_DIRECT) { if ((tapfd = qemuPhysIfaceConnect(vm->def, driver, net, priv->qemuCaps, @@ -803,12 +794,12 @@ int qemuDomainAttachNetDevice(virConnectPtr conn,
if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_NETDEV) && virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_DEVICE)) { - if (!(netstr = qemuBuildHostNetStr(net, driver, priv->qemuCaps, + if (!(netstr = qemuBuildHostNetStr(net, driver, ',', -1, tapfd_name, vhostfd_name))) goto cleanup; } else { - if (!(netstr = qemuBuildHostNetStr(net, driver, priv->qemuCaps, + if (!(netstr = qemuBuildHostNetStr(net, driver, ' ', vlan, tapfd_name, vhostfd_name))) goto cleanup;
I still don't like using qemu-bridge-helper, but this is better than the alternative of having qemu call it (although, due to the way that process capabilities works, we are unable to prevent a rogue qemu started by unprivileged libvirtd from calling it :-(
ACK to this patch (I think I would prefer you left the qemuCaps arg in, but others may disagree with me.)