Merge pull request #26114 from bluca/sd_login_pidfd

sd-login: add sd_pidfd_* APIs

src/basic/process-util.c

@@ -1456,6 +1456,20 @@ int pidfd_get_pid(int fd, pid_t *ret) {
         return parse_pid(p, ret);
 }
 
+int pidfd_verify_pid(int pidfd, pid_t pid) {
+        pid_t current_pid;
+        int r;
+
+        assert(pidfd >= 0);
+        assert(pid > 0);
+
+        r = pidfd_get_pid(pidfd, &current_pid);
+        if (r < 0)
+                return r;
+
+        return current_pid != pid ? -ESRCH : 0;
+}
+
 static int rlimit_to_nice(rlim_t limit) {
         if (limit <= 1)
                 return PRIO_MAX-1; /* i.e. 19 */

src/basic/process-util.h

@@ -190,6 +190,7 @@ assert_cc(TASKS_MAX <= (unsigned long) PID_T_MAX);
         })
 
 int pidfd_get_pid(int fd, pid_t *ret);
+int pidfd_verify_pid(int pidfd, pid_t pid);
 
 int setpriority_closest(int priority);
 

src/core/dbus-manager.c

@@ -658,7 +658,7 @@ static int method_get_unit_by_pidfd(sd_bus_message *message, void *userdata, sd_
         Manager *m = ASSERT_PTR(userdata);
         _cleanup_free_ char *path = NULL;
         int r, pidfd;
-        pid_t pid_early, pid_late;
+        pid_t pid;
         Unit *u;
 
         assert(message);
@@ -667,13 +667,13 @@ static int method_get_unit_by_pidfd(sd_bus_message *message, void *userdata, sd_
         if (r < 0)
                 return r;
 
-        r = pidfd_get_pid(pidfd, &pid_early);
+        r = pidfd_get_pid(pidfd, &pid);
         if (r < 0)
                 return sd_bus_error_set_errnof(error, r, "Failed to get PID from PIDFD: %m");
 
-        u = manager_get_unit_by_pid(m, pid_early);
+        u = manager_get_unit_by_pid(m, pid);
         if (!u)
-                return sd_bus_error_setf(error, BUS_ERROR_NO_UNIT_FOR_PID, "PID "PID_FMT" does not belong to any loaded unit.", pid_early);
+                return sd_bus_error_setf(error, BUS_ERROR_NO_UNIT_FOR_PID, "PID "PID_FMT" does not belong to any loaded unit.", pid);
 
         r = mac_selinux_unit_access_check(u, message, "status", error);
         if (r < 0)
@@ -697,15 +697,14 @@ static int method_get_unit_by_pidfd(sd_bus_message *message, void *userdata, sd_
 
         /* Double-check that the process is still alive and that the PID did not change before returning the
          * answer. */
-        r = pidfd_get_pid(pidfd, &pid_late);
-        if (r < 0)
-                return sd_bus_error_set_errnof(error, r, "Failed to get PID from PIDFD: %m");
-        if (pid_early != pid_late)
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r == -ESRCH)
                 return sd_bus_error_setf(error,
                                          BUS_ERROR_NO_SUCH_PROCESS,
-                                         "The PIDFD's PID "PID_FMT" changed to "PID_FMT" during the lookup operation.",
-                                         pid_early,
-                                         pid_late);
+                                         "The PIDFD's PID "PID_FMT" changed during the lookup operation.",
+                                         pid);
+        if (r < 0)
+                return sd_bus_error_set_errnof(error, r, "Failed to get PID from PIDFD: %m");
 
         return sd_bus_send(NULL, reply, NULL);
 }

src/libsystemd/libsystemd.sym

@@ -802,4 +802,12 @@ global:
         sd_bus_emit_signal_to;
         sd_bus_emit_signal_tov;
         sd_bus_message_new_signal_to;
+        sd_pidfd_get_cgroup;
+        sd_pidfd_get_machine_name;
+        sd_pidfd_get_owner_uid;
+        sd_pidfd_get_session;
+        sd_pidfd_get_slice;
+        sd_pidfd_get_unit;
+        sd_pidfd_get_user_slice;
+        sd_pidfd_get_user_unit;
 } LIBSYSTEMD_252;

src/libsystemd/sd-login/sd-login.c

@@ -22,6 +22,7 @@
 #include "macro.h"
 #include "parse-util.h"
 #include "path-util.h"
+#include "process-util.h"
 #include "socket-util.h"
 #include "stdio-util.h"
 #include "string-util.h"
@@ -134,6 +135,206 @@ _public_ int sd_pid_get_cgroup(pid_t pid, char **cgroup) {
         return 0;
 }
 
+_public_ int sd_pidfd_get_session(int pidfd, char **ret_session) {
+        _cleanup_free_ char *session = NULL;
+        pid_t pid;
+        int r;
+
+        assert_return(pidfd >= 0, -EBADF);
+        assert_return(ret_session, -EINVAL);
+
+        r = pidfd_get_pid(pidfd, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_pid_get_session(pid, &session);
+        if (r < 0)
+                return r;
+
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r < 0)
+                return r;
+
+        *ret_session = TAKE_PTR(session);
+
+        return 0;
+}
+
+_public_ int sd_pidfd_get_unit(int pidfd, char **ret_unit) {
+        _cleanup_free_ char *unit = NULL;
+        pid_t pid;
+        int r;
+
+        assert_return(pidfd >= 0, -EBADF);
+        assert_return(ret_unit, -EINVAL);
+
+        r = pidfd_get_pid(pidfd, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_pid_get_unit(pid, &unit);
+        if (r < 0)
+                return r;
+
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r < 0)
+                return r;
+
+        *ret_unit = TAKE_PTR(unit);
+
+        return 0;
+}
+
+_public_ int sd_pidfd_get_user_unit(int pidfd, char **ret_unit) {
+        _cleanup_free_ char *unit = NULL;
+        pid_t pid;
+        int r;
+
+        assert_return(pidfd >= 0, -EBADF);
+        assert_return(ret_unit, -EINVAL);
+
+        r = pidfd_get_pid(pidfd, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_pid_get_user_unit(pid, &unit);
+        if (r < 0)
+                return r;
+
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r < 0)
+                return r;
+
+        *ret_unit = TAKE_PTR(unit);
+
+        return 0;
+}
+
+_public_ int sd_pidfd_get_machine_name(int pidfd, char **ret_name) {
+        _cleanup_free_ char *name = NULL;
+        pid_t pid;
+        int r;
+
+        assert_return(pidfd >= 0, -EBADF);
+        assert_return(ret_name, -EINVAL);
+
+        r = pidfd_get_pid(pidfd, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_pid_get_machine_name(pid, &name);
+        if (r < 0)
+                return r;
+
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r < 0)
+                return r;
+
+        *ret_name = TAKE_PTR(name);
+
+        return 0;
+}
+
+_public_ int sd_pidfd_get_slice(int pidfd, char **ret_slice) {
+        _cleanup_free_ char *slice = NULL;
+        pid_t pid;
+        int r;
+
+        assert_return(pidfd >= 0, -EBADF);
+        assert_return(ret_slice, -EINVAL);
+
+        r = pidfd_get_pid(pidfd, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_pid_get_slice(pid, &slice);
+        if (r < 0)
+                return r;
+
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r < 0)
+                return r;
+
+        *ret_slice = TAKE_PTR(slice);
+
+        return 0;
+}
+
+_public_ int sd_pidfd_get_user_slice(int pidfd, char **ret_slice) {
+        _cleanup_free_ char *slice = NULL;
+        pid_t pid;
+        int r;
+
+        assert_return(pidfd >= 0, -EBADF);
+        assert_return(ret_slice, -EINVAL);
+
+        r = pidfd_get_pid(pidfd, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_pid_get_user_slice(pid, &slice);
+        if (r < 0)
+                return r;
+
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r < 0)
+                return r;
+
+        *ret_slice = TAKE_PTR(slice);
+
+        return 0;
+}
+
+_public_ int sd_pidfd_get_owner_uid(int pidfd, uid_t *ret_uid) {
+        uid_t uid;
+        pid_t pid;
+        int r;
+
+        assert_return(pidfd >= 0, -EINVAL);
+        assert_return(ret_uid, -EINVAL);
+
+        r = pidfd_get_pid(pidfd, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_pid_get_owner_uid(pid, &uid);
+        if (r < 0)
+                return r;
+
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r < 0)
+                return r;
+
+        *ret_uid = uid;
+
+        return 0;
+}
+
+_public_ int sd_pidfd_get_cgroup(int pidfd, char **ret_cgroup) {
+        _cleanup_free_ char *cgroup = NULL;
+        pid_t pid;
+        int r;
+
+        assert_return(pidfd >= 0, -EBADF);
+        assert_return(ret_cgroup, -EINVAL);
+
+        r = pidfd_get_pid(pidfd, &pid);
+        if (r < 0)
+                return r;
+
+        r = sd_pid_get_cgroup(pid, &cgroup);
+        if (r < 0)
+                return r;
+
+        r = pidfd_verify_pid(pidfd, pid);
+        if (r < 0)
+                return r;
+
+        *ret_cgroup = TAKE_PTR(cgroup);
+
+        return 0;
+}
+
 _public_ int sd_peer_get_session(int fd, char **session) {
         struct ucred ucred = UCRED_INVALID;
         int r;

src/libsystemd/sd-login/test-login.c

@@ -9,6 +9,8 @@
 #include "fd-util.h"
 #include "format-util.h"
 #include "log.h"
+#include "missing_syscall.h"
+#include "process-util.h"
 #include "string-util.h"
 #include "strv.h"
 #include "tests.h"
@@ -44,6 +46,7 @@ TEST(login) {
                 *type = NULL, *class = NULL, *state = NULL, *state2 = NULL,
                 *seat = NULL, *session = NULL,
                 *unit = NULL, *user_unit = NULL, *slice = NULL;
+        _cleanup_close_ int pidfd = -EBADFD;
         int r;
         uid_t u, u2 = UID_INVALID;
         char *t, **seats = NULL, **sessions = NULL;
@@ -71,6 +74,35 @@ TEST(login) {
         log_info("sd_pid_get_cgroup(0, …) → %s / \"%s\"", e(r), strnull(cgroup));
         assert_se(IN_SET(r, 0, -ENOMEDIUM));
 
+        pidfd = pidfd_open(getpid_cached(), 0);
+        if (pidfd >= 0) {
+                _cleanup_free_ char *cgroup2 = NULL, *session2 = NULL,
+                        *unit2 = NULL, *user_unit2 = NULL, *slice2 = NULL;
+
+                r = sd_pidfd_get_unit(pidfd, &unit2);
+                log_info("sd_pidfd_get_unit(pidfd, …) → %s / \"%s\"", e(r), strnull(unit2));
+                assert_se(IN_SET(r, 0, -ENODATA));
+
+                r = sd_pidfd_get_user_unit(pidfd, &user_unit2);
+                log_info("sd_pidfd_get_user_unit(pidfd, …) → %s / \"%s\"", e(r), strnull(user_unit2));
+                assert_se(IN_SET(r, 0, -ENODATA));
+
+                r = sd_pidfd_get_slice(pidfd, &slice2);
+                log_info("sd_pidfd_get_slice(pidfd, …) → %s / \"%s\"", e(r), strnull(slice2));
+                assert_se(IN_SET(r, 0, -ENODATA));
+
+                r = sd_pidfd_get_owner_uid(pidfd, &u2);
+                log_info("sd_pidfd_get_owner_uid(pidfd, …) → %s / "UID_FMT, e(r), u2);
+                assert_se(IN_SET(r, 0, -ENODATA));
+
+                r = sd_pidfd_get_session(pidfd, &session2);
+                log_info("sd_pidfd_get_session(pidfd, …) → %s / \"%s\"", e(r), strnull(session2));
+
+                r = sd_pidfd_get_cgroup(pidfd, &cgroup2);
+                log_info("sd_pidfd_get_cgroup(pidfd, …) → %s / \"%s\"", e(r), strnull(cgroup2));
+                assert_se(IN_SET(r, 0, -ENOMEDIUM));
+        }
+
         r = sd_uid_get_display(u2, &display_session);
         log_info("sd_uid_get_display("UID_FMT", …) → %s / \"%s\"", u2, e(r), strnull(display_session));
         if (u2 == UID_INVALID)

src/systemd/sd-login.h

@@ -80,6 +80,18 @@ int sd_pid_get_machine_name(pid_t pid, char **machine);
  * hierarchy. */
 int sd_pid_get_cgroup(pid_t pid, char **cgroup);
 
+/* Equivalent to the corresponding sd_pid_get* functions, but take a
+ * PIDFD instead of a PID, to ensure there can be no possible PID
+ * recycle issues before/after the calls. */
+int sd_pidfd_get_session(pid_t pid, char **session);
+int sd_pidfd_get_owner_uid(pid_t pid, uid_t *uid);
+int sd_pidfd_get_unit(pid_t pid, char **unit);
+int sd_pidfd_get_user_unit(pid_t pid, char **unit);
+int sd_pidfd_get_slice(pid_t pid, char **slice);
+int sd_pidfd_get_user_slice(pid_t pid, char **slice);
+int sd_pidfd_get_machine_name(pid_t pid, char **machine);
+int sd_pidfd_get_cgroup(pid_t pid, char **cgroup);
+
 /* Similar to sd_pid_get_session(), but retrieves data about the peer
  * of a connected AF_UNIX socket */
 int sd_peer_get_session(int fd, char **session);