[libvirt] [PATCH v1 09/21] qemu: Spawn qemu under mount namespace
Daniel P. Berrange
berrange at redhat.com
Mon Dec 5 13:26:05 UTC 2016
On Thu, Nov 24, 2016 at 03:47:58PM +0100, Michal Privoznik wrote:
> Prime time. When it comes to spawning qemu process and
> relabelling all the devices it's going to touch, there's inherent
> race with other applications in the system (e.g. udev). Instead
> of trying convincing udev to not touch libvirt managed devices,
> we can create a separate mount namespace for the qemu, and mount
> our own /dev there. Of course this puts more work onto us as we
> have to maintain /dev files on each domain start and device
> hot(un-)plug. On the other hand, this enhances security also.
>
> >From technical POV, on domain startup process the parent
> (libvirtd) creates:
>
> /var/lib/libvirt/qemu/$domain.dev
> /var/lib/libvirt/qemu/$domain.devpts
>
> The child (which is going to be qemu eventually) calls unshare()
> to create new mount namespace. From now on anything that child
> does is invisible to the parent. Child then mounts tmpfs on
> $domain.dev (so that it still sees original /dev from the host)
> and creates some devices (as explained in one of the previous
> patches). The devices have to be created exactly as they are in
> the host (including perms, seclabels, ACLs, ...). After that it
> moves $domain.dev mount to /dev.
>
> What's the $domain.devpts mount there for then you ask? QEMU can
> create PTYs for some chardevs. And historically we exposed the
> host ends in our domain XML allowing users to connect to them.
> Therefore we must preserve devpts mount to be shared with the
> host's one.
>
> To make this patch as small as possible, creating of devices
> configured for domain in question is implemented in next patches.
IIUC, this means that QEMU startup will be broken for any guests
that need host devices for disk, usb/pci passthrough, etc ?
It is nice to keep the work incremental though. I wonder if there
is any value in doing everything *except* the MS_MOVE of
/var/lib/libvirt/qemu/$domain.dev -> /dev/. ie only turn it on once
all the code is in place ?
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
> src/qemu/qemu_domain.c | 289 ++++++++++++++++++++++++++++++++++++++++++++++++
> src/qemu/qemu_domain.h | 10 ++
> src/qemu/qemu_process.c | 13 +++
> 3 files changed, 312 insertions(+)
>
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 137d4d5..d6a1c29 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -55,6 +55,9 @@
>
> #include <sys/time.h>
> #include <fcntl.h>
> +#if defined(HAVE_SYS_MOUNT_H)
> +# include <sys/mount.h>
> +#endif
>
> #include <libxml/xpathInternals.h>
>
> @@ -1627,6 +1630,9 @@ qemuDomainObjPrivateXMLFormat(virBufferPtr buf,
> virDomainChrTypeToString(priv->monConfig->type));
> }
>
> + if (priv->containerized)
> + virBufferAddLit(buf, "<containerized/>\n");
I wonder if it is worth explicitly listing the namespaces we enabled ?
eg
<namespaces>
<mount/>
</namespaces>
so we're prepared to deal with us adding use of more private namespaces
in future ?
> +
> qemuDomainObjPrivateXMLFormatVcpus(buf, vm->def);
>
> if (priv->qemuCaps) {
> @@ -1809,6 +1815,8 @@ qemuDomainObjPrivateXMLParse(xmlXPathContextPtr ctxt,
> goto error;
> }
>
> + priv->containerized = virXPathBoolean("count(./containerized) > 0", ctxt) > 0;
> +
> if ((n = virXPathNodeSet("./vcpus/vcpu", ctxt, &nodes)) < 0)
> goto error;
>
> @@ -6653,3 +6661,284 @@ qemuDomainSupportsVideoVga(virDomainVideoDefPtr video,
>
> return true;
> }
> +
> +
> +static int
> +qemuDomainCreateDevice(const char *device,
> + const char *path,
> + bool allow_noent)
> +{
> + char *devicePath = NULL;
> + struct stat sb;
> + int ret = -1;
> +
> + if (!STRPREFIX(device, "/dev")) {
> + virReportError(VIR_ERR_INTERNAL_ERROR,
> + _("invalid device: %s"),
> + device);
> + goto cleanup;
> + }
> +
> + if (virAsprintf(&devicePath, "%s/%s",
> + path, device + 4) < 0)
> + goto cleanup;
> +
> + if (stat(device, &sb) < 0) {
> + if (errno == ENOENT && allow_noent) {
> + /* Ignore non-existent device. */
> + ret = 0;
> + goto cleanup;
> + }
> +
> + virReportSystemError(errno, _("Unable to stat %s"), device);
> + goto cleanup;
> + }
> +
> + if (virFileMakeParentPath(devicePath) < 0) {
> + virReportSystemError(errno,
> + _("Unable to create %s"),
> + devicePath);
> + goto cleanup;
> + }
> +
> + if (mknod(devicePath, sb.st_mode, sb.st_rdev) < 0) {
> + virReportSystemError(errno,
> + _("Failed to make device %s"),
> + devicePath);
> + goto cleanup;
> + }
> +
> + if (chown(devicePath, sb.st_uid, sb.st_gid) < 0) {
> + virReportSystemError(errno,
> + _("Failed to chown device %s"),
> + devicePath);
> + goto cleanup;
> + }
> +
> + if (virFileCopyACLs(device, devicePath) < 0 &&
> + errno != ENOTSUP) {
> + virReportSystemError(errno,
> + _("Failed to copy ACLs on device %s"),
> + devicePath);
> + goto cleanup;
> + }
Per my comments on earlier patches, I don't think we need to have
the chown or ACL copy. Just have the dev owned by root:root and
let our security drivers deal with the rest.
> +
> + ret = 0;
> + cleanup:
> + VIR_FREE(devicePath);
> + return ret;
> +}
> +
> +
> +
> +static int
> +qemuDomainPopulateDevices(virQEMUDriverPtr driver,
> + virDomainObjPtr vm ATTRIBUTE_UNUSED,
> + const char *path)
> +{
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> + const char *const *devices = (const char *const *) cfg->cgroupDeviceACL;
> + size_t i;
> + int ret = -1;
> +
> + if (!devices)
> + devices = defaultDeviceACL;
> +
> + for (i = 0; devices[i]; i++) {
> + if (qemuDomainCreateDevice(devices[i], path, true) < 0)
> + goto cleanup;
> + }
> +
> + ret = 0;
> + cleanup:
> + virObjectUnref(cfg);
> + return ret;
> +}
> +
> +
> +static int
> +qemuDomainSetupDev(virQEMUDriverPtr driver,
> + virDomainObjPtr vm,
> + const char *path)
> +{
> + char *mount_options = NULL;
> + char *opts = NULL;
> + int ret = -1;
> +
> + VIR_DEBUG("Setting up /dev/ for domain %s", vm->def->name);
> +
> + mount_options = virSecurityManagerGetMountOptions(driver->securityManager,
> + vm->def);
> +
> + if (!mount_options &&
> + VIR_STRDUP(mount_options, "") < 0)
> + goto cleanup;
> +
> + /*
> + * tmpfs is limited to 64kb, since we only have device nodes in there
> + * and don't want to DOS the entire OS RAM usage
> + */
> + if (virAsprintf(&opts,
> + "mode=755,size=65536%s", mount_options) < 0)
> + goto cleanup;
> +
> + if (virFileSetupDev(path, opts) < 0)
> + goto cleanup;
> +
> + if (qemuDomainPopulateDevices(driver, vm, path) < 0)
> + goto cleanup;
> +
> + ret = 0;
> + cleanup:
> + VIR_FREE(opts);
> + VIR_FREE(mount_options);
> + return ret;
> +}
> +
> +
> +int
> +qemuDomainBuildNamespace(virQEMUDriverPtr driver,
> + virDomainObjPtr vm)
> +{
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> + qemuDomainObjPrivatePtr priv = vm->privateData;
> + const unsigned long mount_flags = MS_MOVE;
> + char *devPath = NULL;
> + char *devptsPath = NULL;
> + int ret = -1;
> +
> + if (!priv->containerized) {
> + ret = 0;
> + goto cleanup;
> + }
> +
> + if (virAsprintf(&devPath, "%s/%s.dev",
> + cfg->stateDir, vm->def->name) < 0 ||
> + virAsprintf(&devptsPath, "%s/%s.devpts",
> + cfg->stateDir, vm->def->name) < 0)
> + goto cleanup;
> +
> + if (qemuDomainSetupDev(driver, vm, devPath) < 0)
> + goto cleanup;
> +
> + /* Save /dev/pts mount point because /dev/pts/NNN is exposed in our live
> + * XML and other applications are supposed to be able to use it. */
> + if (mount("/dev/pts", devptsPath, NULL, mount_flags, NULL) < 0) {
> + virReportSystemError(errno, "%s",
> + _("Unable to move /dev/pts mount"));
> + goto cleanup;
> + }
> +
> + if (mount(devPath, "/dev", NULL, mount_flags, NULL) < 0) {
> + virReportSystemError(errno,
> + _("Failed to mount %s on /dev"),
> + devPath);
> + goto cleanup;
> + }
> +
> + if (virFileMakePath("/dev/pts") < 0) {
> + virReportSystemError(errno, "%s",
> + _("Cannot create /dev/pts"));
> + goto cleanup;
> + }
> +
> + if (mount(devptsPath, "/dev/pts", NULL, mount_flags, NULL) < 0) {
> + virReportSystemError(errno,
> + _("Failed to mount %s on /dev/pts"),
> + devptsPath);
> + goto cleanup;
> + }
> +
> + if (virFileBindMountDevice("/dev/pts/ptmx", "/dev/ptmx") < 0)
> + goto cleanup;
> +
> + VIR_DEBUG("blaaah: %d", system("find /dev/ -ls > /tmp/blaaah"));
> + VIR_DEBUG("blaaah: %d", system("echo >> /tmp/blaaah"));
> + VIR_DEBUG("blaaah: %d", system("mount >> /tmp/blaaah"));
Heh, :-)
> + ret = 0;
> + cleanup:
> + virObjectUnref(cfg);
> + VIR_FREE(devPath);
> + return ret;
> +}
> +
> +
> +int
> +qemuDomainCreateNamespace(virQEMUDriverPtr driver,
> + virDomainObjPtr vm)
> +{
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> + qemuDomainObjPrivatePtr priv = vm->privateData;
> + int ret = -1;
> + char *path = NULL;
> +
> +#if !defined(__linux__)
> + /* Namespaces are Linux specific. On other platforms just
> + * carry on with the old behaviour. */
> + return 0;
> +#endif
This feels quite likely to create compiler warnings on non-linux
about unreachable code. It feels like we should just stub out
the entire method instead.
> +
> + if (!virQEMUDriverIsPrivileged(driver)) {
> + ret = 0;
> + goto cleanup;
> + }
> +
> + if (virAsprintf(&path, "%s/%s.dev",
> + cfg->stateDir, vm->def->name) < 0)
> + goto cleanup;
> +
> + if (virFileMakePath(path) < 0) {
> + virReportSystemError(errno,
> + _("Failed to create %s"),
> + path);
> + goto cleanup;
> + }
> +
> + VIR_FREE(path);
> + if (virAsprintf(&path, "%s/%s.devpts",
> + cfg->stateDir, vm->def->name) < 0)
> + goto cleanup;
> +
> + if (virFileMakePath(path) < 0) {
> + virReportSystemError(errno,
> + _("Failed to create %s"),
> + path);
> + goto cleanup;
> + }
> +
> + priv->containerized = true;
> + ret = 0;
> + cleanup:
> + VIR_FREE(path);
> + virObjectUnref(cfg);
> + return ret;
> +}
> +
> +
> +void
> +qemuDomainDeleteNamespace(virQEMUDriverPtr driver,
> + virDomainObjPtr vm)
> +{
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> + qemuDomainObjPrivatePtr priv = vm->privateData;
> + char *path;
> +
> + if (!priv->containerized)
> + return;
> +
> + if (virAsprintf(&path, "%s/%s.dev",
> + cfg->stateDir, vm->def->name) < 0)
> + goto cleanup;
> +
> + virFileDeleteTree(path);
> +
> + VIR_FREE(path);
> + if (virAsprintf(&path, "%s/%s.devpts",
> + cfg->stateDir, vm->def->name) < 0)
> + goto cleanup;
> +
> + virFileDeleteTree(path);
> + cleanup:
> + virObjectUnref(cfg);
> + VIR_FREE(path);
> +}
This is running in the host namespace and custom /dev tmpfs
was only ever mounted in the QEMU private namespace, so
should be invisible to the host. As such, IIUC, these
directories should both be 100% empty. IOW, it seems that
we don't need virFileDeleteTree - plain rmdir should be
sufficient and safer against accidents.
> diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
> index 7650ff3..9c34476 100644
> --- a/src/qemu/qemu_domain.h
> +++ b/src/qemu/qemu_domain.h
> @@ -170,6 +170,8 @@ typedef qemuDomainObjPrivate *qemuDomainObjPrivatePtr;
> struct _qemuDomainObjPrivate {
> struct qemuDomainJobObj job;
>
> + bool containerized;
> +
> qemuMonitorPtr mon;
> virDomainChrSourceDefPtr monConfig;
> bool monJSON;
> @@ -785,4 +787,12 @@ int qemuDomainCheckMonitor(virQEMUDriverPtr driver,
> bool qemuDomainSupportsVideoVga(virDomainVideoDefPtr video,
> virQEMUCapsPtr qemuCaps);
>
> +int qemuDomainBuildNamespace(virQEMUDriverPtr driver,
> + virDomainObjPtr vm);
> +
> +int qemuDomainCreateNamespace(virQEMUDriverPtr driver,
> + virDomainObjPtr vm);
> +
> +void qemuDomainDeleteNamespace(virQEMUDriverPtr driver,
> + virDomainObjPtr vm);
> #endif /* __QEMU_DOMAIN_H__ */
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index 93a38e1..4f64dd1 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -2661,6 +2661,12 @@ static int qemuProcessHook(void *data)
> if (virSecurityManagerClearSocketLabel(h->driver->securityManager, h->vm->def) < 0)
> goto cleanup;
>
> + if (virProcessSetupPrivateMountNS() < 0)
> + goto cleanup;
> +
> + if (qemuDomainBuildNamespace(h->driver, h->vm) < 0)
> + goto cleanup;
> +
> if (virDomainNumatuneGetMode(h->vm->def->numa, -1, &mode) == 0) {
> if (mode == VIR_DOMAIN_NUMATUNE_MEM_STRICT &&
> h->cfg->cgroupControllers & (1 << VIR_CGROUP_CONTROLLER_CPUSET) &&
> @@ -5434,6 +5440,11 @@ qemuProcessLaunch(virConnectPtr conn,
>
> qemuDomainLogContextMarkPosition(logCtxt);
>
> + VIR_DEBUG("Building mount namespace");
> +
> + if (qemuDomainCreateNamespace(driver, vm) < 0)
> + goto cleanup;
> +
> VIR_DEBUG("Clear emulator capabilities: %d",
> cfg->clearEmulatorCapabilities);
> if (cfg->clearEmulatorCapabilities)
> @@ -6210,6 +6221,8 @@ void qemuProcessStop(virQEMUDriverPtr driver,
> }
> }
>
> + qemuDomainDeleteNamespace(driver, vm);
> +
> vm->taint = 0;
> vm->pid = -1;
> virDomainObjSetState(vm, VIR_DOMAIN_SHUTOFF, reason);
Regards,
Daniel
--
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