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core: when Delegate=yes is set for a unit, run ExecStartPre= and friends in a subcgroup of the unit

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Otherwise we might conflict with the "no-processes-in-inner-cgroup" rule
of cgroupsv2. Consider nspawn starting up and initializing its cgroup
hierarchy with "supervisor/" and "payload/" as subcgroup, with itself
moved into the former and the payload into the latter. Now, if an
ExecStartPre= is run right after it cannot be placed in the main cgroup,
because that is now in inner cgroup with populated children.

Hence, let's run these helpers in another sub-cgroup .control/ below it.

This is somewhat ugly since it weakens the clear separation of
ownership, but given that this is an explicit contract, and double opt-in should be acceptable.

Fixes: #10482
This commit is contained in:
Lennart Poettering 2018-11-16 20:19:07 +01:00
parent a0ee3d93bb
commit 78f93209fc
3 changed files with 70 additions and 19 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

67
src/core/execute.c
View file

@ -2762,6 +2762,37 @@ static int compile_suggested_paths(const ExecContext *c, const ExecParameters *p
static char *exec_command_line(char **argv);
static int exec_parameters_get_cgroup_path(const ExecParameters *params, char **ret) {
bool using_subcgroup;
char *p;
assert(params);
assert(ret);
if (!params->cgroup_path)
return -EINVAL;
/* If we are called for a unit where cgroup delegation is on, and the payload created its own populated
* subcgroup (which we expect it to do, after all it asked for delegation), then we cannot place the control
* processes started after the main unit's process in the unit's main cgroup because it is now an inner one,
* and inner cgroups may not contain processes. Hence, if delegation is on, and this is a control process,
* let's use ".control" as subcgroup instead. Note that we do so only for ExecStartPost=, ExecReload=,
* ExecStop=, ExecStopPost=, i.e. for the commands where the main process is already forked. For ExecStartPre=
* this is not necessary, the cgroup is still empty. We distinguish these cases with the EXEC_CONTROL_CGROUP
* flag, which is only passed for the former statements, not for the latter. */
using_subcgroup = FLAGS_SET(params->flags, EXEC_CONTROL_CGROUP|EXEC_CGROUP_DELEGATE|EXEC_IS_CONTROL);
if (using_subcgroup)
p = strjoin(params->cgroup_path, "/.control");
else
p = strdup(params->cgroup_path);
if (!p)
return -ENOMEM;
*ret = p;
return using_subcgroup;
}
static int exec_child(
Unit *unit,
const ExecCommand *command,
@ -2994,10 +3025,18 @@ static int exec_child(
}
if (params->cgroup_path) {
r = cg_attach_everywhere(params->cgroup_supported, params->cgroup_path, 0, NULL, NULL);
_cleanup_free_ char *p = NULL;
r = exec_parameters_get_cgroup_path(params, &p);
if (r < 0) {
*exit_status = EXIT_CGROUP;
return log_unit_error_errno(unit, r, "Failed to attach to cgroup %s: %m", params->cgroup_path);
return log_unit_error_errno(unit, r, "Failed to acquire cgroup path: %m");
}
r = cg_attach_everywhere(params->cgroup_supported, p, 0, NULL, NULL);
if (r < 0) {
*exit_status = EXIT_CGROUP;
return log_unit_error_errno(unit, r, "Failed to attach to cgroup %s: %m", p);
}
}
@ -3569,6 +3608,7 @@ int exec_spawn(Unit *unit,
pid_t *ret) {
int socket_fd, r, named_iofds[3] = { -1, -1, -1 }, *fds = NULL;
_cleanup_free_ char *subcgroup_path = NULL;
_cleanup_strv_free_ char **files_env = NULL;
size_t n_storage_fds = 0, n_socket_fds = 0;
_cleanup_free_ char *line = NULL;
@ -3621,6 +3661,17 @@ int exec_spawn(Unit *unit,
LOG_UNIT_ID(unit),
LOG_UNIT_INVOCATION_ID(unit));
if (params->cgroup_path) {
r = exec_parameters_get_cgroup_path(params, &subcgroup_path);
if (r < 0)
return log_unit_error_errno(unit, r, "Failed to acquire subcgroup path: %m");
if (r > 0) { /* We are using a child cgroup */
r = cg_create(SYSTEMD_CGROUP_CONTROLLER, subcgroup_path);
if (r < 0)
return log_unit_error_errno(unit, r, "Failed to create control group '%s': %m", subcgroup_path);
}
}
pid = fork();
if (pid < 0)
return log_unit_error_errno(unit, errno, "Failed to fork: %m");
@ -3658,13 +3709,11 @@ int exec_spawn(Unit *unit,
log_unit_debug(unit, "Forked %s as "PID_FMT, command->path, pid);
/* We add the new process to the cgroup both in the child (so
* that we can be sure that no user code is ever executed
* outside of the cgroup) and in the parent (so that we can be
* sure that when we kill the cgroup the process will be
* killed too). */
if (params->cgroup_path)
(void) cg_attach(SYSTEMD_CGROUP_CONTROLLER, params->cgroup_path, pid);
/* We add the new process to the cgroup both in the child (so that we can be sure that no user code is ever
* executed outside of the cgroup) and in the parent (so that we can be sure that when we kill the cgroup the
* process will be killed too). */
if (subcgroup_path)
(void) cg_attach(SYSTEMD_CGROUP_CONTROLLER, subcgroup_path, pid);
exec_status_start(&command->exec_status, pid);

9
src/core/execute.h
View file

@ -294,12 +294,13 @@ typedef enum ExecFlags {
EXEC_CHOWN_DIRECTORIES = 1 << 5, /* chown() the runtime/state/cache/log directories to the user we run as, under all conditions */
EXEC_NSS_BYPASS_BUS = 1 << 6, /* Set the SYSTEMD_NSS_BYPASS_BUS environment variable, to disable nss-systemd for dbus */
EXEC_CGROUP_DELEGATE = 1 << 7,
EXEC_IS_CONTROL = 1 << 8,
EXEC_CONTROL_CGROUP = 1 << 9, /* Place the process not in the indicated cgroup but in a subcgroup '/.control', but only EXEC_CGROUP_DELEGATE and EXEC_IS_CONTROL is set, too */
/* The following are not used by execute.c, but by consumers internally */
EXEC_PASS_FDS = 1 << 8,
EXEC_IS_CONTROL = 1 << 9,
EXEC_SETENV_RESULT = 1 << 10,
EXEC_SET_WATCHDOG = 1 << 11,
EXEC_PASS_FDS = 1 << 10,
EXEC_SETENV_RESULT = 1 << 11,
EXEC_SET_WATCHDOG = 1 << 12,
} ExecFlags;
/* Parameters for a specific invocation of a command. This structure is put together right before a command is

13
src/core/service.c
View file

@ -1418,7 +1418,7 @@ static int service_spawn(
assert(c);
assert(_pid);
r = unit_prepare_exec(UNIT(s));
r = unit_prepare_exec(UNIT(s)); /* This realizes the cgroup, among other things */
if (r < 0)
return r;
@ -1777,7 +1777,7 @@ static void service_enter_stop_post(Service *s, ServiceResult f) {
r = service_spawn(s,
s->control_command,
s->timeout_stop_usec,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_APPLY_TTY_STDIN|EXEC_IS_CONTROL|EXEC_SETENV_RESULT,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_APPLY_TTY_STDIN|EXEC_IS_CONTROL|EXEC_SETENV_RESULT|EXEC_CONTROL_CGROUP,
&s->control_pid);
if (r < 0)
goto fail;
@ -1892,7 +1892,7 @@ static void service_enter_stop(Service *s, ServiceResult f) {
r = service_spawn(s,
s->control_command,
s->timeout_stop_usec,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_IS_CONTROL|EXEC_SETENV_RESULT,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_IS_CONTROL|EXEC_SETENV_RESULT|EXEC_CONTROL_CGROUP,
&s->control_pid);
if (r < 0)
goto fail;
@ -1970,7 +1970,7 @@ static void service_enter_start_post(Service *s) {
r = service_spawn(s,
s->control_command,
s->timeout_start_usec,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_IS_CONTROL,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_IS_CONTROL|EXEC_CONTROL_CGROUP,
&s->control_pid);
if (r < 0)
goto fail;
@ -2214,7 +2214,7 @@ static void service_enter_reload(Service *s) {
r = service_spawn(s,
s->control_command,
s->timeout_start_usec,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_IS_CONTROL,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_IS_CONTROL|EXEC_CONTROL_CGROUP,
&s->control_pid);
if (r < 0)
goto fail;
@ -2254,7 +2254,8 @@ static void service_run_next_control(Service *s) {
timeout,
EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_IS_CONTROL|
(IN_SET(s->control_command_id, SERVICE_EXEC_START_PRE, SERVICE_EXEC_STOP_POST) ? EXEC_APPLY_TTY_STDIN : 0)|
(IN_SET(s->control_command_id, SERVICE_EXEC_STOP, SERVICE_EXEC_STOP_POST) ? EXEC_SETENV_RESULT : 0),
(IN_SET(s->control_command_id, SERVICE_EXEC_STOP, SERVICE_EXEC_STOP_POST) ? EXEC_SETENV_RESULT : 0)|
(IN_SET(s->control_command_id, SERVICE_EXEC_START_POST, SERVICE_EXEC_RELOAD, SERVICE_EXEC_STOP, SERVICE_EXEC_STOP_POST) ? EXEC_CONTROL_CGROUP : 0),
&s->control_pid);
if (r < 0)
goto fail;