libbb: use _exit, not exit, in bb_daemonize_or_rexec()

By the time we reach exit in parent, child already exited or execed.
We should not re-run libc cleanup code.

While at it, introduce bb_daemon_helper() and add a few comments.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

6 files changed, 22 insertions, 15 deletions

diff --git a/console-tools/openvt.c b/console-tools/openvt.c
index f3db28367..423122fe9 100644
--- a/console-tools/openvt.c
+++ b/console-tools/openvt.c
@@ -99,7 +99,7 @@ static int find_free_vtno(void)
         /*xfunc_error_retval = 3; - do we need compat? */
         if (ioctl(fd, VT_OPENQRY, &vtno) != 0 || vtno <= 0)
                 bb_perror_msg_and_die("can't find open VT");
-// Not really needed, grep for DAEMON_ONLY_SANITIZE
+// Not really needed, grep for DAEMON_CLOSE_EXTRA_FDS
 //      if (fd > 2)
 //              close(fd);
         return vtno;
@@ -155,7 +155,7 @@ int openvt_main(int argc UNUSED_PARAM, char **argv)
         /* Grab new VT */
         sprintf(vtname, VC_FORMAT, vtno);
         /* (Try to) clean up stray open fds above fd 2 */
-        bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS | DAEMON_ONLY_SANITIZE, NULL);
+        bb_daemon_helper(DAEMON_CLOSE_EXTRA_FDS);
         close(STDIN_FILENO);
         /*setsid(); - BAD IDEA: after we exit, child is SIGHUPed... */
         xopen(vtname, O_RDWR);
diff --git a/debianutils/start_stop_daemon.c b/debianutils/start_stop_daemon.c
index 9d60b2c7f..07c104baa 100644
--- a/debianutils/start_stop_daemon.c
+++ b/debianutils/start_stop_daemon.c
@@ -516,6 +516,11 @@ int start_stop_daemon_main(int argc UNUSED_PARAM, char **argv)
                 /* DAEMON_DEVNULL_STDIO is superfluous -
                  * it's always done by bb_daemonize() */
 #else
+                /* Daemons usually call bb_daemonize_or_rexec(), but SSD can do
+                 * without: SSD is not itself a daemon, it _execs_ a daemon.
+                 * The usual NOMMU problem of "child can't run indefinitely,
+                 * it must exec" does not bite us: we exec anyway.
+                 */
                 pid_t pid = xvfork();
                 if (pid != 0) {
                         /* parent */
@@ -525,12 +530,8 @@ int start_stop_daemon_main(int argc UNUSED_PARAM, char **argv)
                 }
                 /* Child */
                 setsid(); /* detach from controlling tty */
-                /* Redirect stdio to /dev/null, close extra FDs.
-                 * We do not actually daemonize because of DAEMON_ONLY_SANITIZE */
-                bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO
-                        + DAEMON_CLOSE_EXTRA_FDS
-                        + DAEMON_ONLY_SANITIZE,
-                        NULL /* argv, unused */ );
+                /* Redirect stdio to /dev/null, close extra FDs */
+                bb_daemon_helper(DAEMON_DEVNULL_STDIO + DAEMON_CLOSE_EXTRA_FDS);
 #endif
         }
         if (opt & OPT_MAKEPID) {
diff --git a/include/libbb.h b/include/libbb.h
index bb27c59a1..6a2a2d640 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1169,6 +1169,7 @@ enum {
 #endif
 void bb_daemonize_or_rexec(int flags, char **argv) FAST_FUNC;
 void bb_sanitize_stdio(void) FAST_FUNC;
+#define bb_daemon_helper(arg) bb_daemonize_or_rexec((arg) | DAEMON_ONLY_SANITIZE, NULL)
 /* Clear dangerous stuff, set PATH. Return 1 if was run by different user. */
 int sanitize_env_if_suid(void) FAST_FUNC;
 
diff --git a/libbb/vfork_daemon_rexec.c b/libbb/vfork_daemon_rexec.c
index 98512bb00..f84e678b5 100644
--- a/libbb/vfork_daemon_rexec.c
+++ b/libbb/vfork_daemon_rexec.c
@@ -209,6 +209,9 @@ pid_t FAST_FUNC fork_or_rexec(char **argv)
         /* Maybe we are already re-execed and come here again? */
         if (re_execed)
                 return 0;
+
+        /* fflush_all(); ? - so far all callers had no buffered output to flush */
+
         pid = xvfork();
         if (pid) /* parent */
                 return pid;
@@ -245,8 +248,11 @@ void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
                 fd = dup(fd); /* have 0,1,2 open at least to /dev/null */
 
         if (!(flags & DAEMON_ONLY_SANITIZE)) {
+
+                /* fflush_all(); - add it in fork_or_rexec() if necessary */
+
                 if (fork_or_rexec(argv))
-                        exit(EXIT_SUCCESS); /* parent */
+                        _exit(EXIT_SUCCESS); /* parent */
                 /* if daemonizing, detach from stdio & ctty */
                 setsid();
                 dup2(fd, 0);
@@ -258,7 +264,7 @@ void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
                          * Prevent this: stop being a session leader.
                          */
                         if (fork_or_rexec(argv))
-                                exit(EXIT_SUCCESS); /* parent */
+                                _exit(EXIT_SUCCESS); /* parent */
                 }
         }
         while (fd > 2) {
diff --git a/loginutils/login.c b/loginutils/login.c
index 381468d81..fcdb9592c 100644
--- a/loginutils/login.c
+++ b/loginutils/login.c
@@ -350,8 +350,8 @@ int login_main(int argc UNUSED_PARAM, char **argv)
         /* Mandatory paranoia for suid applet:
          * ensure that fd# 0,1,2 are opened (at least to /dev/null)
          * and any extra open fd's are closed.
-         * (The name of the function is misleading. Not daemonizing here.) */
-        bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);
+         */
+        bb_daemon_helper(DAEMON_CLOSE_EXTRA_FDS);
 
         username[0] = '\0';
         opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
diff --git a/printutils/lpd.c b/printutils/lpd.c
index 3fdba5d2b..662d3a224 100644
--- a/printutils/lpd.c
+++ b/printutils/lpd.c
@@ -198,9 +198,8 @@ int lpd_main(int argc UNUSED_PARAM, char *argv[])
                                 q = p; // next line
                         }
                         // helper should not talk over network.
-                        // this call reopens stdio fds to "/dev/null"
-                        // (no daemonization is done)
-                        bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL);
+                        // this call reopens stdio fds to "/dev/null".
+                        bb_daemon_helper(DAEMON_DEVNULL_STDIO);
                         BB_EXECVP_or_die(argv);
                 }