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logind: support deserializing session leader through pidfdid

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People make weird assumptions around state preservation and
expect logind to be stoppable. While this is realistically
not OK we can probably improve things a little.

This complements f01d8658a3 and
adds support for deserializing the LEADER_PIDFDID= field.
We still prioritize pidfd if got one from fdstore (as with
service_notify_message_parse_new_pid() in pid1), but otherwise
this should make logind restart more robust when fdstore
gets spuriously cleared.

Fixes #39437
This commit is contained in:
Mike Yuan
2025-10-24 23:09:50 +02:00
parent f03b49b079
commit 45eea629e3
2 changed files with 68 additions and 24 deletions
Download Patch File Download Diff File Expand all files Collapse all files

68
src/login/logind-session.c
View File

@@ -409,6 +409,46 @@ static int session_load_devices(Session *s, const char *devices) {
return r;
}
static int session_load_leader(Session *s, uint64_t pidfdid) {
_cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
int r;
assert(s);
assert(pid_is_valid(s->deserialized_pid));
assert(!pidref_is_set(&s->leader));
if (pidfdid == 0 && s->leader_fd_saved)
/* We have no pidfd id for stable reference, but the pidfd has been submitted to fdstore.
* manager_enumerate_fds() will dispatch the leader fd for us later. */
return 0;
r = pidref_set_pid(&pidref, s->deserialized_pid);
if (r < 0)
return log_error_errno(r, "Failed to deserialize leader PID for session '%s': %m", s->id);
if (pidref.fd < 0)
return log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE),
"Failed to acquire pidfd for session leader '" PID_FMT "', refusing.",
pidref.pid);
if (pidfdid > 0) {
r = pidref_acquire_pidfd_id(&pidref);
if (r < 0)
return log_error_errno(r, "Failed to acquire pidfd id of deserialized leader '" PID_FMT "': %m",
pidref.pid);
if (pidref.fd_id != pidfdid)
return log_error_errno(SYNTHETIC_ERRNO(ESRCH),
"Deserialized pidfd id for process " PID_FMT " (%" PRIu64 ") doesn't match with the current one (%" PRIu64 "), refusing.",
pidref.pid, pidfdid, pidref.fd_id);
}
r = session_set_leader_consume(s, TAKE_PIDREF(pidref));
if (r < 0)
return log_error_errno(r, "Failed to set leader PID for session '%s': %m", s->id);
return 1;
}
int session_load(Session *s) {
_cleanup_free_ char *remote = NULL,
*seat = NULL,
@@ -418,6 +458,7 @@ int session_load(Session *s) {
*position = NULL,
*leader_pid = NULL,
*leader_fd_saved = NULL,
*leader_pidfdid = NULL,
*type = NULL,
*original_type = NULL,
*class = NULL,
@@ -452,6 +493,7 @@ int session_load(Session *s) {
"POSITION", &position,
"LEADER", &leader_pid,
"LEADER_FD_SAVED", &leader_fd_saved,
"LEADER_PIDFDID", &leader_pidfdid,
"TYPE", &type,
"ORIGINAL_TYPE", &original_type,
"CLASS", &class,
@@ -594,8 +636,6 @@ int session_load(Session *s) {
}
if (leader_pid) {
assert(!pidref_is_set(&s->leader));
r = parse_pid(leader_pid, &s->deserialized_pid);
if (r < 0)
return log_error_errno(r, "Failed to parse LEADER=%s: %m", leader_pid);
@@ -605,25 +645,19 @@ int session_load(Session *s) {
if (r < 0)
return log_error_errno(r, "Failed to parse LEADER_FD_SAVED=%s: %m", leader_fd_saved);
s->leader_fd_saved = r > 0;
if (s->leader_fd_saved)
/* The leader fd will be acquired from fdstore later */
return 0;
}
_cleanup_(pidref_done) PidRef p = PIDREF_NULL;
uint64_t pidfdid;
if (leader_pidfdid) {
r = safe_atou64(leader_pidfdid, &pidfdid);
if (r < 0)
return log_error_errno(r, "Failed to parse LEADER_PIDFDID=%s: %m", leader_pidfdid);
} else
pidfdid = 0;
r = pidref_set_pid(&p, s->deserialized_pid);
r = session_load_leader(s, pidfdid);
if (r < 0)
return log_error_errno(r, "Failed to deserialize leader PID for session '%s': %m", s->id);
if (p.fd < 0)
return log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE),
"Failed to acquire pidfd for session leader '" PID_FMT "', refusing.",
p.pid);
r = session_set_leader_consume(s, TAKE_PIDREF(p));
if (r < 0)
return log_error_errno(r, "Failed to set leader PID for session '%s': %m", s->id);
return r;
}
return 0;

24
src/login/logind.c
View File

@@ -40,6 +40,7 @@
#include "process-util.h"
#include "service-util.h"
#include "signal-util.h"
#include "stat-util.h"
#include "strv.h"
#include "terminal-util.h"
#include "udev-util.h"
@@ -448,19 +449,28 @@ static int deliver_session_leader_fd_consume(Session *s, const char *fdname, int
assert(fdname);
assert(fd >= 0);
if (!pid_is_valid(s->deserialized_pid)) {
/* Already deserialized via pidfd id? */
if (pidref_is_set(&s->leader)) {
assert(s->leader.pid == s->deserialized_pid);
assert(s->leader.fd >= 0);
r = fd_inode_same(fd, s->leader.fd);
if (r < 0)
return log_warning_errno(r, "Failed to compare pidfd with deserialized leader for session '%s': %m",
s->id);
if (r > 0)
return 0;
log_warning("Got leader pidfd for session '%s' which mismatches with the deserialized process, resetting with pidfd.",
s->id);
} else if (!pid_is_valid(s->deserialized_pid)) {
r = log_warning_errno(SYNTHETIC_ERRNO(EOWNERDEAD),
"Got leader pidfd for session '%s', but LEADER= is not set, refusing.",
s->id);
goto fail_close;
}
if (!s->leader_fd_saved)
log_warning("Got leader pidfd for session '%s', but not recorded in session state, proceeding anyway.",
s->id);
else
assert(!pidref_is_set(&s->leader));
r = pidref_set_pidfd_take(&leader_fdstore, fd);
if (r < 0) {
if (r == -ESRCH)