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, 31 insertions, 11 deletions

diff --git a/src/journal/journald.c b/src/journal/journald.c
index 1bf25e8091..619a98d1f2 100644
--- a/src/journal/journald.c
+++ b/src/journal/journald.c
@@ -77,6 +77,7 @@
 
 typedef enum StdoutStreamState {
         STDOUT_STREAM_IDENTIFIER,
+        STDOUT_STREAM_UNIT_ID,
         STDOUT_STREAM_PRIORITY,
         STDOUT_STREAM_LEVEL_PREFIX,
         STDOUT_STREAM_FORWARD_TO_SYSLOG,
@@ -97,6 +98,7 @@ struct StdoutStream {
 #endif
 
         char *identifier;
+        char *unit_id;
         int priority;
         bool level_prefix:1;
         bool forward_to_syslog:1;
@@ -458,7 +460,7 @@ static void dispatch_message_real(
                 struct iovec *iovec, unsigned n, unsigned m,
                 struct ucred *ucred,
                 struct timeval *tv,
-                const char *label, size_t label_len) {
+                const char *label, size_t label_len, const char *unit_id) {
 
         char *pid = NULL, *uid = NULL, *gid = NULL,
                 *source_time = NULL, *boot_id = NULL, *machine_id = NULL,
@@ -560,10 +562,11 @@ static void dispatch_message_real(
                 if (cg_pid_get_unit(ucred->pid, &t) >= 0) {
                         unit = strappend("_SYSTEMD_UNIT=", t);
                         free(t);
+                } else if (unit_id)
+                        unit = strappend("_SYSTEMD_UNIT=", unit_id);
 
-                        if (unit)
-                                IOVEC_SET_STRING(iovec[n++], unit);
-                }
+                if (unit)
+                        IOVEC_SET_STRING(iovec[n++], unit);
 
 #ifdef HAVE_SELINUX
                 if (label) {
@@ -702,7 +705,7 @@ static void driver_message(Server *s, sd_id128_t message_id, const char *format,
         ucred.uid = getuid();
         ucred.gid = getgid();
 
-        dispatch_message_real(s, iovec, n, ELEMENTSOF(iovec), &ucred, NULL, NULL, 0);
+        dispatch_message_real(s, iovec, n, ELEMENTSOF(iovec), &ucred, NULL, NULL, 0, NULL);
 }
 
 static void dispatch_message(Server *s,
@@ -710,6 +713,7 @@ static void dispatch_message(Server *s,
                              struct ucred *ucred,
                              struct timeval *tv,
                              const char *label, size_t label_len,
+                             const char *unit_id,
                              int priority) {
         int rl;
         char *path = NULL, *c;
@@ -760,7 +764,7 @@ static void dispatch_message(Server *s,
         free(path);
 
 finish:
-        dispatch_message_real(s, iovec, n, m, ucred, tv, label, label_len);
+        dispatch_message_real(s, iovec, n, m, ucred, tv, label, label_len, unit_id);
 }
 
 static void forward_syslog_iovec(Server *s, const struct iovec *iovec, unsigned n_iovec, struct ucred *ucred, struct timeval *tv) {
@@ -1126,7 +1130,7 @@ static void process_syslog_message(Server *s, const char *buf, struct ucred *ucr
         if (message)
                 IOVEC_SET_STRING(iovec[n++], message);
 
-        dispatch_message(s, iovec, n, ELEMENTSOF(iovec), ucred, tv, label, label_len, priority);
+        dispatch_message(s, iovec, n, ELEMENTSOF(iovec), ucred, tv, label, label_len, NULL, priority);
 
         free(message);
         free(identifier);
@@ -1204,7 +1208,7 @@ static void process_native_message(
 
                 if (e == p) {
                         /* Entry separator */
-                        dispatch_message(s, iovec, n, m, ucred, tv, label, label_len, priority);
+                        dispatch_message(s, iovec, n, m, ucred, tv, label, label_len, NULL, priority);
                         n = 0;
                         priority = LOG_INFO;
 
@@ -1354,7 +1358,7 @@ static void process_native_message(
                         forward_console(s, priority, identifier, message, ucred);
         }
 
-        dispatch_message(s, iovec, n, m, ucred, tv, label, label_len, priority);
+        dispatch_message(s, iovec, n, m, ucred, tv, label, label_len, NULL, priority);
 
 finish:
         for (j = 0; j < n; j++)  {
@@ -1477,7 +1481,7 @@ static int stdout_stream_log(StdoutStream *s, const char *p) {
         }
 #endif
 
-        dispatch_message(s->server, iovec, n, ELEMENTSOF(iovec), &s->ucred, NULL, label, label_len, priority);
+        dispatch_message(s->server, iovec, n, ELEMENTSOF(iovec), &s->ucred, NULL, label, label_len, s->unit_id, priority);
 
         free(message);
         free(syslog_priority);
@@ -1508,6 +1512,22 @@ static int stdout_stream_line(StdoutStream *s, char *p) {
                         }
                 }
 
+                s->state = STDOUT_STREAM_UNIT_ID;
+                return 0;
+
+        case STDOUT_STREAM_UNIT_ID:
+                if (s->ucred.uid == 0) {
+                        if (isempty(p))
+                                s->unit_id = NULL;
+                        else  {
+                                s->unit_id = strdup(p);
+                                if (!s->unit_id) {
+                                        log_error("Out of memory");
+                                        return -ENOMEM;
+                                }
+                        }
+                }
+
                 s->state = STDOUT_STREAM_PRIORITY;
                 return 0;
 
@@ -1874,7 +1894,7 @@ static void proc_kmsg_line(Server *s, const char *p) {
         if (message)
                 IOVEC_SET_STRING(iovec[n++], message);
 
-        dispatch_message(s, iovec, n, ELEMENTSOF(iovec), NULL, NULL, NULL, 0, priority);
+        dispatch_message(s, iovec, n, ELEMENTSOF(iovec), NULL, NULL, NULL, 0, NULL, priority);
 
 finish:
         free(message);