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core: introduce new Type=exec service type

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Users are often surprised that "systemd-run" command lines like
"systemd-run -p User=idontexist /bin/true" will return successfully,
even though the logs show that the process couldn't be invoked, as the
user "idontexist" doesn't exist. This is because Type=simple will only
wait until fork() succeeded before returning start-up success.

This patch adds a new service type Type=exec, which is very similar to
Type=simple, but waits until the child process completed the execve()
before returning success. It uses a pipe that has O_CLOEXEC set for this
logic, so that the kernel automatically sends POLLHUP on it when the
execve() succeeded but leaves the pipe open if not. This means PID 1
waits exactly until the execve() succeeded in the child, and not longer
and not shorter, which is the desired functionality.

Making use of this new functionality, the command line
"systemd-run -p User=idontexist -p Type=exec /bin/true" will now fail,
as expected.
This commit is contained in:
Lennart Poettering 2018-07-17 11:47:14 +02:00
parent ce0d60a7c4
commit 5686391b00
7 changed files with 255 additions and 29 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

91
src/core/execute.c
View file

@ -2573,6 +2573,7 @@ static int close_remaining_fds(
const DynamicCreds *dcreds,
int user_lookup_fd,
int socket_fd,
int exec_fd,
int *fds, size_t n_fds) {
size_t n_dont_close = 0;
@ -2589,6 +2590,8 @@ static int close_remaining_fds(
if (socket_fd >= 0)
dont_close[n_dont_close++] = socket_fd;
if (exec_fd >= 0)
dont_close[n_dont_close++] = exec_fd;
if (n_fds > 0) {
memcpy(dont_close + n_dont_close, fds, sizeof(int) * n_fds);
n_dont_close += n_fds;
@ -2732,9 +2735,10 @@ static int exec_child(
int *exit_status) {
_cleanup_strv_free_ char **our_env = NULL, **pass_env = NULL, **accum_env = NULL, **final_argv = NULL;
_cleanup_free_ char *home_buffer = NULL;
int *fds_with_exec_fd, n_fds_with_exec_fd, r, ngids = 0, exec_fd = -1;
_cleanup_free_ gid_t *supplementary_gids = NULL;
const char *username = NULL, *groupname = NULL;
_cleanup_free_ char *home_buffer = NULL;
const char *home = NULL, *shell = NULL;
dev_t journal_stream_dev = 0;
ino_t journal_stream_ino = 0;
@ -2754,7 +2758,6 @@ static int exec_child(
#endif
uid_t uid = UID_INVALID;
gid_t gid = GID_INVALID;
int r, ngids = 0;
size_t n_fds;
ExecDirectoryType dt;
int secure_bits;
@ -2798,8 +2801,8 @@ static int exec_child(
/* In case anything used libc syslog(), close this here, too */
closelog();
n_fds = n_storage_fds + n_socket_fds;
r = close_remaining_fds(params, runtime, dcreds, user_lookup_fd, socket_fd, fds, n_fds);
n_fds = n_socket_fds + n_storage_fds;
r = close_remaining_fds(params, runtime, dcreds, user_lookup_fd, socket_fd, params->exec_fd, fds, n_fds);
if (r < 0) {
*exit_status = EXIT_FDS;
return log_unit_error_errno(unit, r, "Failed to close unwanted file descriptors: %m");
@ -3172,9 +3175,45 @@ static int exec_child(
}
/* We repeat the fd closing here, to make sure that nothing is leaked from the PAM modules. Note that we are
* more aggressive this time since socket_fd and the netns fds we don't need anymore. The custom endpoint fd
* was needed to upload the policy and can now be closed as well. */
r = close_all_fds(fds, n_fds);
* more aggressive this time since socket_fd and the netns fds we don't need anymore. We do keep the exec_fd
* however if we have it as we want to keep it open until the final execve(). */
if (params->exec_fd >= 0) {
exec_fd = params->exec_fd;
if (exec_fd < 3 + (int) n_fds) {
int moved_fd;
/* Let's move the exec fd far up, so that it's outside of the fd range we want to pass to the
* process we are about to execute. */
moved_fd = fcntl(exec_fd, F_DUPFD_CLOEXEC, 3 + (int) n_fds);
if (moved_fd < 0) {
*exit_status = EXIT_FDS;
return log_unit_error_errno(unit, errno, "Couldn't move exec fd up: %m");
}
safe_close(exec_fd);
exec_fd = moved_fd;
} else {
/* This fd should be FD_CLOEXEC already, but let's make sure. */
r = fd_cloexec(exec_fd, true);
if (r < 0) {
*exit_status = EXIT_FDS;
return log_unit_error_errno(unit, r, "Failed to make exec fd FD_CLOEXEC: %m");
}
}
fds_with_exec_fd = newa(int, n_fds + 1);
memcpy(fds_with_exec_fd, fds, n_fds * sizeof(int));
fds_with_exec_fd[n_fds] = exec_fd;
n_fds_with_exec_fd = n_fds + 1;
} else {
fds_with_exec_fd = fds;
n_fds_with_exec_fd = n_fds;
}
r = close_all_fds(fds_with_exec_fd, n_fds_with_exec_fd);
if (r >= 0)
r = shift_fds(fds, n_fds);
if (r >= 0)
@ -3184,6 +3223,11 @@ static int exec_child(
return log_unit_error_errno(unit, r, "Failed to adjust passed file descriptors: %m");
}
/* At this point, the fds we want to pass to the program are all ready and set up, with O_CLOEXEC turned off
* and at the right fd numbers. The are no other fds open, with one exception: the exec_fd if it is defined,
* and it has O_CLOEXEC set, after all we want it to be closed by the execve(), so that our parent knows we
* came this far. */
secure_bits = context->secure_bits;
if (needs_sandboxing) {
@ -3414,10 +3458,35 @@ static int exec_child(
LOG_UNIT_INVOCATION_ID(unit));
}
execve(command->path, final_argv, accum_env);
if (exec_fd >= 0) {
uint8_t hot = 1;
if (errno == ENOENT && (command->flags & EXEC_COMMAND_IGNORE_FAILURE)) {
log_struct_errno(LOG_INFO, errno,
/* We have finished with all our initializations. Let's now let the manager know that. From this point
* on, if the manager sees POLLHUP on the exec_fd, then execve() was successful. */
if (write(exec_fd, &hot, sizeof(hot)) < 0) {
*exit_status = EXIT_EXEC;
return log_unit_error_errno(unit, errno, "Failed to enable exec_fd: %m");
}
}
execve(command->path, final_argv, accum_env);
r = -errno;
if (exec_fd >= 0) {
uint8_t hot = 0;
/* The execve() failed. This means the exec_fd is still open. Which means we need to tell the manager
* that POLLHUP on it no longer means execve() succeeded. */
if (write(exec_fd, &hot, sizeof(hot)) < 0) {
*exit_status = EXIT_EXEC;
return log_unit_error_errno(unit, errno, "Failed to disable exec_fd: %m");
}
}
if (r == -ENOENT && (command->flags & EXEC_COMMAND_IGNORE_FAILURE)) {
log_struct_errno(LOG_INFO, r,
"MESSAGE_ID=" SD_MESSAGE_SPAWN_FAILED_STR,
LOG_UNIT_ID(unit),
LOG_UNIT_INVOCATION_ID(unit),
@ -3428,7 +3497,7 @@ static int exec_child(
}
*exit_status = EXIT_EXEC;
return log_unit_error_errno(unit, errno, "Failed to execute command: %m");
return log_unit_error_errno(unit, r, "Failed to execute command: %m");
}
static int exec_context_load_environment(const Unit *unit, const ExecContext *c, char ***l);

3
src/core/execute.h
View file

@ -317,6 +317,9 @@ struct ExecParameters {
int stdin_fd;
int stdout_fd;
int stderr_fd;
/* An fd that is closed by the execve(), and thus will result in EOF when the execve() is done */
int exec_fd;
};
#include "unit.h"

9
src/core/mount.c
View file

@ -747,10 +747,11 @@ static void mount_dump(Unit *u, FILE *f, const char *prefix) {
static int mount_spawn(Mount *m, ExecCommand *c, pid_t *_pid) {
ExecParameters exec_params = {
.flags = EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_APPLY_TTY_STDIN,
.stdin_fd = -1,
.stdout_fd = -1,
.stderr_fd = -1,
.flags = EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_APPLY_TTY_STDIN,
.stdin_fd = -1,
.stdout_fd = -1,
.stderr_fd = -1,
.exec_fd = -1,
};
pid_t pid;
int r;

167
src/core/service.c
View file

@ -79,9 +79,10 @@ static const UnitActiveState state_translation_table_idle[_SERVICE_STATE_MAX] =
[SERVICE_AUTO_RESTART] = UNIT_ACTIVATING
};
static int service_dispatch_io(sd_event_source *source, int fd, uint32_t events, void *userdata);
static int service_dispatch_inotify_io(sd_event_source *source, int fd, uint32_t events, void *userdata);
static int service_dispatch_timer(sd_event_source *source, usec_t usec, void *userdata);
static int service_dispatch_watchdog(sd_event_source *source, usec_t usec, void *userdata);
static int service_dispatch_exec_io(sd_event_source *source, int fd, uint32_t events, void *userdata);
static void service_enter_signal(Service *s, ServiceState state, ServiceResult f);
static void service_enter_reload_by_notify(Service *s);
@ -389,6 +390,7 @@ static void service_done(Unit *u) {
service_stop_watchdog(s);
s->timer_event_source = sd_event_source_unref(s->timer_event_source);
s->exec_fd_event_source = sd_event_source_unref(s->exec_fd_event_source);
service_release_resources(u);
}
@ -1066,6 +1068,9 @@ static void service_set_state(Service *s, ServiceState state) {
!(state == SERVICE_DEAD && UNIT(s)->job))
service_close_socket_fd(s);
if (state != SERVICE_START)
s->exec_fd_event_source = sd_event_source_unref(s->exec_fd_event_source);
if (!IN_SET(state, SERVICE_START_POST, SERVICE_RUNNING, SERVICE_RELOAD))
service_stop_watchdog(s);
@ -1296,6 +1301,63 @@ static int service_collect_fds(
return 0;
}
static int service_allocate_exec_fd_event_source(
Service *s,
int fd,
sd_event_source **ret_event_source) {
_cleanup_(sd_event_source_unrefp) sd_event_source *source = NULL;
int r;
assert(s);
assert(fd >= 0);
assert(ret_event_source);
r = sd_event_add_io(UNIT(s)->manager->event, &source, fd, 0, service_dispatch_exec_io, s);
if (r < 0)
return log_unit_error_errno(UNIT(s), r, "Failed to allocate exec_fd event source: %m");
/* This is a bit lower priority than SIGCHLD, as that carries a lot more interesting failure information */
r = sd_event_source_set_priority(source, SD_EVENT_PRIORITY_NORMAL-3);
if (r < 0)
return log_unit_error_errno(UNIT(s), r, "Failed to adjust priority of exec_fd event source: %m");
(void) sd_event_source_set_description(source, "service event_fd");
r = sd_event_source_set_io_fd_own(source, true);
if (r < 0)
return log_unit_error_errno(UNIT(s), r, "Failed to pass ownership of fd to event source: %m");
*ret_event_source = TAKE_PTR(source);
return 0;
}
static int service_allocate_exec_fd(
Service *s,
sd_event_source **ret_event_source,
int* ret_exec_fd) {
_cleanup_close_pair_ int p[2] = { -1, -1 };
int r;
assert(s);
assert(ret_event_source);
assert(ret_exec_fd);
if (pipe2(p, O_CLOEXEC|O_NONBLOCK) < 0)
return log_unit_error_errno(UNIT(s), errno, "Failed to allocate exec_fd pipe: %m");
r = service_allocate_exec_fd_event_source(s, p[0], ret_event_source);
if (r < 0)
return r;
p[0] = -1;
*ret_exec_fd = TAKE_FD(p[1]);
return 0;
}
static bool service_exec_needs_notify_socket(Service *s, ExecFlags flags) {
assert(s);
@ -1330,7 +1392,9 @@ static int service_spawn(
.exec_fd = -1,
};
_cleanup_strv_free_ char **final_env = NULL, **our_env = NULL, **fd_names = NULL;
_cleanup_(sd_event_source_unrefp) sd_event_source *exec_fd_source = NULL;
size_t n_socket_fds = 0, n_storage_fds = 0, n_env = 0;
_cleanup_close_ int exec_fd = -1;
_cleanup_free_ int *fds = NULL;
pid_t pid;
int r;
@ -1363,6 +1427,14 @@ static int service_spawn(
log_unit_debug(UNIT(s), "Passing %zu fds to service", n_socket_fds + n_storage_fds);
}
if (!FLAGS_SET(flags, EXEC_IS_CONTROL) && s->type == SERVICE_EXEC) {
assert(!s->exec_fd_event_source);
r = service_allocate_exec_fd(s, &exec_fd_source, &exec_fd);
if (r < 0)
return r;
}
r = service_arm_timer(s, usec_add(now(CLOCK_MONOTONIC), timeout));
if (r < 0)
return r;
@ -1462,6 +1534,7 @@ static int service_spawn(
exec_params.stdin_fd = s->stdin_fd;
exec_params.stdout_fd = s->stdout_fd;
exec_params.stderr_fd = s->stderr_fd;
exec_params.exec_fd = exec_fd;
r = exec_spawn(UNIT(s),
c,
@ -1473,6 +1546,9 @@ static int service_spawn(
if (r < 0)
return r;
s->exec_fd_event_source = TAKE_PTR(exec_fd_source);
s->exec_fd_hot = false;
r = unit_watch_pid(UNIT(s), pid);
if (r < 0) /* FIXME: we need to do something here */
return r;
@ -1984,14 +2060,12 @@ static void service_enter_start(Service *s) {
s->control_pid = pid;
service_set_state(s, SERVICE_START);
} else if (IN_SET(s->type, SERVICE_ONESHOT, SERVICE_DBUS, SERVICE_NOTIFY)) {
} else if (IN_SET(s->type, SERVICE_ONESHOT, SERVICE_DBUS, SERVICE_NOTIFY, SERVICE_EXEC)) {
/* For oneshot services we wait until the start
* process exited, too, but it is our main process. */
/* For oneshot services we wait until the start process exited, too, but it is our main process. */
/* For D-Bus services we know the main pid right away,
* but wait for the bus name to appear on the
* bus. Notify services are similar. */
/* For D-Bus services we know the main pid right away, but wait for the bus name to appear on the
* bus. 'notify' and 'exec' services are similar. */
service_set_main_pid(s, pid);
service_set_state(s, SERVICE_START);
@ -2444,6 +2518,13 @@ static int service_serialize(Unit *u, FILE *f, FDSet *fds) {
if (r < 0)
return r;
if (s->exec_fd_event_source) {
r = unit_serialize_item_fd(u, f, fds, "exec-fd", sd_event_source_get_io_fd(s->exec_fd_event_source));
if (r < 0)
return r;
unit_serialize_item(u, f, "exec-fd-hot", yes_no(s->exec_fd_hot));
}
if (UNIT_ISSET(s->accept_socket)) {
r = unit_serialize_item(u, f, "accept-socket", UNIT_DEREF(s->accept_socket)->id);
if (r < 0)
@ -2777,6 +2858,18 @@ static int service_deserialize_item(Unit *u, const char *key, const char *value,
s->stderr_fd = fdset_remove(fds, fd);
s->exec_context.stdio_as_fds = true;
}
} else if (streq(key, "exec-fd")) {
int fd;
if (safe_atoi(value, &fd) < 0 || fd < 0 || !fdset_contains(fds, fd))
log_unit_debug(u, "Failed to parse exec-fd value: %s", value);
else {
s->exec_fd_event_source = sd_event_source_unref(s->exec_fd_event_source);
fd = fdset_remove(fds, fd);
if (service_allocate_exec_fd_event_source(s, fd, &s->exec_fd_event_source) < 0)
safe_close(fd);
}
} else if (streq(key, "watchdog-override-usec")) {
usec_t watchdog_override_usec;
if (timestamp_deserialize(value, &watchdog_override_usec) < 0)
@ -2860,7 +2953,7 @@ static int service_watch_pid_file(Service *s) {
log_unit_debug(UNIT(s), "Setting watch for PID file %s", s->pid_file_pathspec->path);
r = path_spec_watch(s->pid_file_pathspec, service_dispatch_io);
r = path_spec_watch(s->pid_file_pathspec, service_dispatch_inotify_io);
if (r < 0)
goto fail;
@ -2904,7 +2997,7 @@ static int service_demand_pid_file(Service *s) {
return service_watch_pid_file(s);
}
static int service_dispatch_io(sd_event_source *source, int fd, uint32_t events, void *userdata) {
static int service_dispatch_inotify_io(sd_event_source *source, int fd, uint32_t events, void *userdata) {
PathSpec *p = userdata;
Service *s;
@ -2937,6 +3030,59 @@ fail:
return 0;
}
static int service_dispatch_exec_io(sd_event_source *source, int fd, uint32_t events, void *userdata) {
Service *s = SERVICE(userdata);
assert(s);
log_unit_debug(UNIT(s), "got exec-fd event");
/* If Type=exec is set, we'll consider a service started successfully the instant we invoked execve()
* successfully for it. We implement this through a pipe() towards the child, which the kernel automatically
* closes for us due to O_CLOEXEC on execve() in the child, which then triggers EOF on the pipe in the
* parent. We need to be careful however, as there are other reasons that we might cause the child's side of
* the pipe to be closed (for example, a simple exit()). To deal with that we'll ignore EOFs on the pipe unless
* the child signalled us first that it is about to call the execve(). It does so by sending us a simple
* non-zero byte via the pipe. We also provide the child with a way to inform us in case execve() failed: if it
* sends a zero byte we'll ignore POLLHUP on the fd again. */
for (;;) {
uint8_t x;
ssize_t n;
n = read(fd, &x, sizeof(x));
if (n < 0) {
if (errno == EAGAIN) /* O_NONBLOCK in effect → everything queued has now been processed. */
return 0;
return log_unit_error_errno(UNIT(s), errno, "Failed to read from exec_fd: %m");
}
if (n == 0) { /* EOF → the event we are waiting for */
s->exec_fd_event_source = sd_event_source_unref(s->exec_fd_event_source);
if (s->exec_fd_hot) { /* Did the child tell us to expect EOF now? */
log_unit_debug(UNIT(s), "Got EOF on exec-fd");
s->exec_fd_hot = false;
/* Nice! This is what we have been waiting for. Transition to next state. */
if (s->type == SERVICE_EXEC && s->state == SERVICE_START)
service_enter_start_post(s);
} else
log_unit_debug(UNIT(s), "Got EOF on exec-fd while it was disabled, ignoring.");
return 0;
}
/* A byte was read → this turns on/off the exec fd logic */
assert(n == sizeof(x));
s->exec_fd_hot = x;
}
return 0;
}
static void service_notify_cgroup_empty_event(Unit *u) {
Service *s = SERVICE(u);
@ -3846,7 +3992,8 @@ static const char* const service_type_table[_SERVICE_TYPE_MAX] = {
[SERVICE_ONESHOT] = "oneshot",
[SERVICE_DBUS] = "dbus",
[SERVICE_NOTIFY] = "notify",
[SERVICE_IDLE] = "idle"
[SERVICE_IDLE] = "idle",
[SERVICE_EXEC] = "exec",
};
DEFINE_STRING_TABLE_LOOKUP(service_type, ServiceType);

4
src/core/service.h
View file

@ -30,6 +30,7 @@ typedef enum ServiceType {
SERVICE_DBUS, /* we fork and wait until a specific D-Bus name appears on the bus */
SERVICE_NOTIFY, /* we fork and wait until a daemon sends us a ready message with sd_notify() */
SERVICE_IDLE, /* much like simple, but delay exec() until all jobs are dispatched. */
SERVICE_EXEC, /* we fork and wait until we execute exec() (this means our own setup is waited for) */
_SERVICE_TYPE_MAX,
_SERVICE_TYPE_INVALID = -1
} ServiceType;
@ -165,6 +166,8 @@ struct Service {
NotifyAccess notify_access;
NotifyState notify_state;
sd_event_source *exec_fd_event_source;
ServiceFDStore *fd_store;
size_t n_fd_store;
unsigned n_fd_store_max;
@ -179,6 +182,7 @@ struct Service {
unsigned n_restarts;
bool flush_n_restarts;
bool exec_fd_hot;
};
extern const UnitVTable service_vtable;

9
src/core/socket.c
View file

@ -1867,10 +1867,11 @@ static int socket_coldplug(Unit *u) {
static int socket_spawn(Socket *s, ExecCommand *c, pid_t *_pid) {
ExecParameters exec_params = {
.flags = EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_APPLY_TTY_STDIN,
.stdin_fd = -1,
.stdout_fd = -1,
.stderr_fd = -1,
.flags = EXEC_APPLY_SANDBOXING|EXEC_APPLY_CHROOT|EXEC_APPLY_TTY_STDIN,
.stdin_fd = -1,
.stdout_fd = -1,
.stderr_fd = -1,
.exec_fd = -1,
};
pid_t pid;
int r;

1
src/core/swap.c
View file

@ -606,6 +606,7 @@ static int swap_spawn(Swap *s, ExecCommand *c, pid_t *_pid) {
.stdin_fd = -1,
.stdout_fd = -1,
.stderr_fd = -1,
.exec_fd = -1,
};
pid_t pid;
int r;