journal: set the _SYSTEMD_UNIT field for messages from terminated processes

As described in

  https://bugs.freedesktop.org/show_bug.cgi?id=50184

the journal currently doesn't set fields such as _SYSTEMD_UNIT
properly for messages coming from processes that have already
terminated.  This means among other things that "systemctl status" may
not show some of the output of services that wrote messages just
before they exited.

This patch fixes this by having processes that log to the journal
write their unit identifier to journald when the connection to
/run/systemd/journal/stdout is opened.  Journald stores the unit ID
and uses it to fill in _SYSTEMD_UNIT when it cannot be obtained
normally (i.e. from the cgroup).  To prevent impersonating another
unit, this information is only used when the caller is root.

This doesn't fix the general problem of getting metadata about
messages from terminated processes (which requires some kernel
support), but it allows "systemctl status" and similar queries to do
the Right Thing for units that log via stdout/stderr.

1 files changed, 10 insertions, 7 deletions

diff --git a/src/core/execute.c b/src/core/execute.c
index bbc430e055..01dceb0788 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -176,7 +176,7 @@ static int open_null_as(int flags, int nfd) {
         return r;
 }
 
-static int connect_logger_as(const ExecContext *context, ExecOutput output, const char *ident, int nfd) {
+static int connect_logger_as(const ExecContext *context, ExecOutput output, const char *ident, const char *unit_id, int nfd) {
         int fd, r;
         union sockaddr_union sa;
 
@@ -206,12 +206,14 @@ static int connect_logger_as(const ExecContext *context, ExecOutput output, cons
 
         dprintf(fd,
                 "%s\n"
+                "%s\n"
                 "%i\n"
                 "%i\n"
                 "%i\n"
                 "%i\n"
                 "%i\n",
                 context->syslog_identifier ? context->syslog_identifier : ident,
+                unit_id,
                 context->syslog_priority,
                 !!context->syslog_level_prefix,
                 output == EXEC_OUTPUT_SYSLOG || output == EXEC_OUTPUT_SYSLOG_AND_CONSOLE,
@@ -311,7 +313,7 @@ static int setup_input(const ExecContext *context, int socket_fd, bool apply_tty
         }
 }
 
-static int setup_output(const ExecContext *context, int socket_fd, const char *ident, bool apply_tty_stdin) {
+static int setup_output(const ExecContext *context, int socket_fd, const char *ident, const char *unit_id, bool apply_tty_stdin) {
         ExecOutput o;
         ExecInput i;
 
@@ -358,7 +360,7 @@ static int setup_output(const ExecContext *context, int socket_fd, const char *i
         case EXEC_OUTPUT_KMSG_AND_CONSOLE:
         case EXEC_OUTPUT_JOURNAL:
         case EXEC_OUTPUT_JOURNAL_AND_CONSOLE:
-                return connect_logger_as(context, o, ident, STDOUT_FILENO);
+                return connect_logger_as(context, o, ident, unit_id, STDOUT_FILENO);
 
         case EXEC_OUTPUT_SOCKET:
                 assert(socket_fd >= 0);
@@ -369,7 +371,7 @@ static int setup_output(const ExecContext *context, int socket_fd, const char *i
         }
 }
 
-static int setup_error(const ExecContext *context, int socket_fd, const char *ident, bool apply_tty_stdin) {
+static int setup_error(const ExecContext *context, int socket_fd, const char *ident, const char *unit_id, bool apply_tty_stdin) {
         ExecOutput o, e;
         ExecInput i;
 
@@ -413,7 +415,7 @@ static int setup_error(const ExecContext *context, int socket_fd, const char *id
         case EXEC_OUTPUT_KMSG_AND_CONSOLE:
         case EXEC_OUTPUT_JOURNAL:
         case EXEC_OUTPUT_JOURNAL_AND_CONSOLE:
-                return connect_logger_as(context, e, ident, STDERR_FILENO);
+                return connect_logger_as(context, e, ident, unit_id, STDERR_FILENO);
 
         case EXEC_OUTPUT_SOCKET:
                 assert(socket_fd >= 0);
@@ -913,6 +915,7 @@ int exec_spawn(ExecCommand *command,
                CGroupBonding *cgroup_bondings,
                CGroupAttribute *cgroup_attributes,
                const char *cgroup_suffix,
+               const char *unit_id,
                int idle_pipe[2],
                pid_t *ret) {
 
@@ -1101,14 +1104,14 @@ int exec_spawn(ExecCommand *command,
                 }
 
                 if (!keep_stdout) {
-                        err = setup_output(context, socket_fd, path_get_file_name(command->path), apply_tty_stdin);
+                        err = setup_output(context, socket_fd, path_get_file_name(command->path), unit_id, apply_tty_stdin);
                         if (err < 0) {
                                 r = EXIT_STDOUT;
                                 goto fail_child;
                         }
                 }
 
-                err = setup_error(context, socket_fd, path_get_file_name(command->path), apply_tty_stdin);
+                err = setup_error(context, socket_fd, path_get_file_name(command->path), unit_id, apply_tty_stdin);
                 if (err < 0) {
                         r = EXIT_STDERR;
                         goto fail_child;