Re: [libvirt PATCHv3 10/12] qemu: add code for handling virtiofsd

On Thu, Jan 30, 2020 at 06:06:26PM +0100, Ján Tomko wrote: > Start virtiofsd for each <filesystem> device using it. > > Pre-create the socket for communication with QEMU and pass it > to virtiofsd. > > Note that virtiofsd needs to run as root. So we're not able to use virtiofsd with the session libvirtd which runs completely unprivileged ?

I can understand the need to run as root if we want to support chown() of files, or DAC_OVERRIDE, but I'm surprised it isn't possible to run virtiofsd unprivileged & simply have a reduced featureset where it can only create files as that one user.

> +int > +qemuVirtioFSStart(virLogManagerPtr logManager, > + virQEMUDriverPtr driver, > + virDomainObjPtr vm, > + virDomainFSDefPtr fs) > +{ > + g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(driver); > + g_autoptr(virCommand) cmd = NULL; > + g_autofree char *socket_path = NULL; > + g_autofree char *pidfile = NULL; > + g_autofree char *logpath = NULL; > + pid_t pid = (pid_t) -1; > + VIR_AUTOCLOSE fd = -1; > + VIR_AUTOCLOSE logfd = -1; > + int ret = -1; > + int rc; > + > + if (!(pidfile = qemuVirtioFSCreatePidFilename(cfg, vm->def, fs->info.alias))) > + goto cleanup; > + > + if (!(socket_path = qemuVirtioFSCreateSocketFilename(vm, fs->info.alias))) > + goto cleanup; > + > + if ((fd = qemuVirtioFSOpenChardev(driver, vm, socket_path)) < 0) > + goto cleanup; > + > + logpath = qemuVirtioFSCreateLogFilename(cfg, vm->def, fs->info.alias); > + > + if (cfg->stdioLogD) { > + if ((logfd = virLogManagerDomainOpenLogFile(logManager, > + "qemu", > + vm->def->uuid, > + vm->def->name, > + logpath, > + 0, > + NULL, NULL)) < 0) > + goto cleanup; > + } else { > + if ((logfd = open(logpath, O_WRONLY | O_CREAT | O_APPEND, S_IRUSR | S_IWUSR)) < 0) { > + virReportSystemError(errno, _("failed to create logfile %s"), > + logpath); > + goto cleanup; > + } > + if (virSetCloseExec(logfd) < 0) { > + virReportSystemError(errno, _("failed to set close-on-exec flag on %s"), > + logpath); > + goto error; > + } > + } > + > + if (!(cmd = qemuVirtioFSBuildCommandLine(cfg, fs, &fd))) > + goto cleanup; > + > + virCommandSetPidFile(cmd, pidfile); > + virCommandSetOutputFD(cmd, &logfd); > + virCommandSetErrorFD(cmd, &logfd); > + virCommandNonblockingFDs(cmd); > + virCommandDaemonize(cmd); We're not mandating "root" here, it is just inheriting the user that libvirtd runs as. So IIUC ,this will run virtofsd as non-root when used with session libvirtd, unless there's a check somewhere else that prevents this scenario ?

I'm also wondering about cgroups placement in this method, and any use of SELinux

> + > + if (qemuExtDeviceLogCommand(driver, vm, cmd, "virtiofsd") < 0) > + goto cleanup; > + > + rc = virCommandRun(cmd, NULL); > + logfd = -1;