nscd: Improved support for tracking startup failure in nscd service (BZ #16639)

Currently, the nscd parent process parses commandline options and
configuration, forks on startup and immediately exits with a success.
If the child process encounters some error after this, it goes
undetected and any services started up after it may have to repeatedly
check to make sure that the nscd service did actually start up and is
serving requests.

To make this process more reliable, I have added a pipe between the
parent and child process, through which the child process sends a
notification to the parent informing it of its status.  The parent
waits for this status and once it receives it, exits with the
corresponding exit code.  So if the child service sends a success
status (0), the parent exits with a success status.  Similarly for
error conditions, the child sends the non-zero status code, which the
parent passes on as the exit code.

This, along with setting the nscd service type to forking in its
systemd configuration file, allows systemd to be certain that the nscd
service is ready and is accepting connections.

1 files changed, 25 insertions, 23 deletions

diff --git a/nscd/connections.c b/nscd/connections.c
index f463f45..180ae77 100644
--- a/nscd/connections.c
+++ b/nscd/connections.c
@@ -649,8 +649,8 @@ cannot create read-only descriptor for \"%s\"; no mmap"),
 		  close (fd);
 	      }
 	    else if (errno == EACCES)
-	      error (EXIT_FAILURE, 0, _("cannot access '%s'"),
-		     dbs[cnt].db_filename);
+	      do_exit (EXIT_FAILURE, 0, _("cannot access '%s'"),
+		       dbs[cnt].db_filename);
 	  }
 
 	if (dbs[cnt].head == NULL)
@@ -699,8 +699,7 @@ cannot create read-only descriptor for \"%s\"; no mmap"),
 		  {
 		    dbg_log (_("database for %s corrupted or simultaneously used; remove %s manually if necessary and restart"),
 			     dbnames[cnt], dbs[cnt].db_filename);
-		    // XXX Correct way to terminate?
-		    exit (1);
+		    do_exit (1, 0, NULL);
 		  }
 
 		if  (dbs[cnt].persistent)
@@ -867,7 +866,7 @@ cannot set socket to close on exec: %s; disabling paranoia mode"),
   if (sock < 0)
     {
       dbg_log (_("cannot open socket: %s"), strerror (errno));
-      exit (errno == EACCES ? 4 : 1);
+      do_exit (errno == EACCES ? 4 : 1, 0, NULL);
     }
   /* Bind a name to the socket.  */
   struct sockaddr_un sock_addr;
@@ -876,7 +875,7 @@ cannot set socket to close on exec: %s; disabling paranoia mode"),
   if (bind (sock, (struct sockaddr *) &sock_addr, sizeof (sock_addr)) < 0)
     {
       dbg_log ("%s: %s", _PATH_NSCDSOCKET, strerror (errno));
-      exit (errno == EACCES ? 4 : 1);
+      do_exit (errno == EACCES ? 4 : 1, 0, NULL);
     }
 
 #ifndef __ASSUME_SOCK_CLOEXEC
@@ -888,7 +887,7 @@ cannot set socket to close on exec: %s; disabling paranoia mode"),
 	{
 	  dbg_log (_("cannot change socket to nonblocking mode: %s"),
 		   strerror (errno));
-	  exit (1);
+	  do_exit (1, 0, NULL);
 	}
 
       /* The descriptor needs to be closed on exec.  */
@@ -896,7 +895,7 @@ cannot set socket to close on exec: %s; disabling paranoia mode"),
 	{
 	  dbg_log (_("cannot set socket to close on exec: %s"),
 		   strerror (errno));
-	  exit (1);
+	  do_exit (1, 0, NULL);
 	}
     }
 #endif
@@ -909,7 +908,7 @@ cannot set socket to close on exec: %s; disabling paranoia mode"),
     {
       dbg_log (_("cannot enable socket to accept connections: %s"),
 	       strerror (errno));
-      exit (1);
+      do_exit (1, 0, NULL);
     }
 
 #ifdef HAVE_NETLINK
@@ -953,7 +952,7 @@ cannot set socket to close on exec: %s; disabling paranoia mode"),
 		      dbg_log (_("\
 cannot change socket to nonblocking mode: %s"),
 			       strerror (errno));
-		      exit (1);
+		      do_exit (1, 0, NULL);
 		    }
 
 		  /* The descriptor needs to be closed on exec.  */
@@ -962,7 +961,7 @@ cannot change socket to nonblocking mode: %s"),
 		    {
 		      dbg_log (_("cannot set socket to close on exec: %s"),
 			       strerror (errno));
-		      exit (1);
+		      do_exit (1, 0, NULL);
 		    }
 		}
 # endif
@@ -2392,7 +2391,7 @@ start_threads (void)
       if (pthread_cond_init (&dbs[i].prune_cond, &condattr) != 0)
 	{
 	  dbg_log (_("could not initialize conditional variable"));
-	  exit (1);
+	  do_exit (1, 0, NULL);
 	}
 
       pthread_t th;
@@ -2400,7 +2399,7 @@ start_threads (void)
 	  && pthread_create (&th, &attr, nscd_run_prune, (void *) i) != 0)
 	{
 	  dbg_log (_("could not start clean-up thread; terminating"));
-	  exit (1);
+	  do_exit (1, 0, NULL);
 	}
     }
 
@@ -2414,13 +2413,17 @@ start_threads (void)
 	  if (i == 0)
 	    {
 	      dbg_log (_("could not start any worker thread; terminating"));
-	      exit (1);
+	      do_exit (1, 0, NULL);
 	    }
 
 	  break;
 	}
     }
 
+  /* Now it is safe to let the parent know that we're doing fine and it can
+     exit.  */
+  notify_parent (0);
+
   /* Determine how much room for descriptors we should initially
      allocate.  This might need to change later if we cap the number
      with MAXCONN.  */
@@ -2465,8 +2468,8 @@ begin_drop_privileges (void)
   if (pwd == NULL)
     {
       dbg_log (_("Failed to run nscd as user '%s'"), server_user);
-      error (EXIT_FAILURE, 0, _("Failed to run nscd as user '%s'"),
-	     server_user);
+      do_exit (EXIT_FAILURE, 0,
+	       _("Failed to run nscd as user '%s'"), server_user);
     }
 
   server_uid = pwd->pw_uid;
@@ -2483,7 +2486,8 @@ begin_drop_privileges (void)
     {
       /* This really must never happen.  */
       dbg_log (_("Failed to run nscd as user '%s'"), server_user);
-      error (EXIT_FAILURE, errno, _("initial getgrouplist failed"));
+      do_exit (EXIT_FAILURE, errno,
+	       _("initial getgrouplist failed"));
     }
 
   server_groups = (gid_t *) xmalloc (server_ngroups * sizeof (gid_t));
@@ -2492,7 +2496,7 @@ begin_drop_privileges (void)
       == -1)
     {
       dbg_log (_("Failed to run nscd as user '%s'"), server_user);
-      error (EXIT_FAILURE, errno, _("getgrouplist failed"));
+      do_exit (EXIT_FAILURE, errno, _("getgrouplist failed"));
     }
 }
 
@@ -2510,7 +2514,7 @@ finish_drop_privileges (void)
   if (setgroups (server_ngroups, server_groups) == -1)
     {
       dbg_log (_("Failed to run nscd as user '%s'"), server_user);
-      error (EXIT_FAILURE, errno, _("setgroups failed"));
+      do_exit (EXIT_FAILURE, errno, _("setgroups failed"));
     }
 
   int res;
@@ -2521,8 +2525,7 @@ finish_drop_privileges (void)
   if (res == -1)
     {
       dbg_log (_("Failed to run nscd as user '%s'"), server_user);
-      perror ("setgid");
-      exit (4);
+      do_exit (4, errno, "setgid");
     }
 
   if (paranoia)
@@ -2532,8 +2535,7 @@ finish_drop_privileges (void)
   if (res == -1)
     {
       dbg_log (_("Failed to run nscd as user '%s'"), server_user);
-      perror ("setuid");
-      exit (4);
+      do_exit (4, errno, "setuid");
     }
 
 #if defined HAVE_LIBAUDIT && defined HAVE_LIBCAP