7 #include <sys/socket.h>
14 void service_record::run_child_proc(const char * const *args, const char *logfile, bool on_console,
15 int wpipefd, int csfd, int socket_fd, uid_t uid, gid_t gid) noexcept
17 // Child process. Must not allocate memory (or otherwise risk throwing any exception)
18 // from here until exit().
20 // If the console already has a session leader, presumably it is us. On the other hand
21 // if it has no session leader, and we don't create one, then control inputs such as
22 // ^C will have no effect.
23 bool do_set_ctty = (tcgetsid(0) == -1);
25 // Copy signal mask, but unmask signals that we masked on startup. For the moment, we'll
26 // also block all signals, since apparently dup() can be interrupted (!!! really, POSIX??).
29 sigfillset(&sigall_set);
30 sigprocmask(SIG_SETMASK, &sigall_set, &sigwait_set);
31 sigdelset(&sigwait_set, SIGCHLD);
32 sigdelset(&sigwait_set, SIGINT);
33 sigdelset(&sigwait_set, SIGTERM);
34 sigdelset(&sigwait_set, SIGQUIT);
36 constexpr int bufsz = ((CHAR_BIT * sizeof(pid_t)) / 3 + 2) + 11;
37 // "LISTEN_PID=" - 11 characters; the expression above gives a conservative estimate
38 // on the maxiumum number of bytes required for LISTEN=nnn, including nul terminator,
39 // where nnn is a pid_t in decimal (i.e. one decimal digit is worth just over 3 bits).
42 // "DINIT_CS_FD=" - 12 bytes. (we -1 from sizeof(int) in account of sign bit).
43 constexpr int csenvbufsz = ((CHAR_BIT * sizeof(int) - 1) / 3 + 2) + 12;
44 char csenvbuf[csenvbufsz];
46 int minfd = (socket_fd == -1) ? 3 : 4;
48 // Move wpipefd/csfd to another fd if necessary
49 if (wpipefd < minfd) {
50 wpipefd = fcntl(wpipefd, F_DUPFD_CLOEXEC, minfd);
51 if (wpipefd == -1) goto failure_out;
54 if (csfd != -1 && csfd < minfd) {
55 csfd = fcntl(csfd, F_DUPFD, minfd);
56 if (csfd == -1) goto failure_out;
59 if (socket_fd != -1) {
60 // If we passing a pre-opened socket, it has to be fd number 3. (Thanks, systemd).
61 if (dup2(socket_fd, 3) == -1) goto failure_out;
66 if (putenv(const_cast<char *>("LISTEN_FDS=1"))) goto failure_out;
67 snprintf(nbuf, bufsz, "LISTEN_PID=%jd", static_cast<intmax_t>(getpid()));
68 if (putenv(nbuf)) goto failure_out;
72 snprintf(csenvbuf, csenvbufsz, "DINIT_CS_FD=%d", csfd);
73 if (putenv(csenvbuf)) goto failure_out;
77 // Re-set stdin, stdout, stderr
78 close(0); close(1); close(2);
80 if (open("/dev/null", O_RDONLY) == 0) {
81 // stdin = 0. That's what we should have; proceed with opening
83 if (open(logfile, O_WRONLY | O_CREAT | O_APPEND, S_IRUSR | S_IWUSR) != 1) {
86 if (dup2(1, 2) != 2) {
90 else goto failure_out;
92 // We have the option of creating a session and process group, or just a new process
93 // group. If we just create a new process group, the child process cannot make itself
94 // a session leader if it wants to do that (eg getty/login will generally want this).
95 // If we do neither, and we are running with a controlling terminal, a ^C or similar
96 // will also affect the child process (which probably isn't so bad, though since we
97 // will handle the shutdown ourselves it's not necessary). Creating a new session
98 // (and a new process group as part of that) seems like a safe bet, and has the
99 // advantage of letting us signal the process as part of a process group.
103 // "run on console" - run as a foreground job on the terminal/console device
105 // if do_set_ctty is false, we are the session leader; we are probably running
106 // as a user process. Don't create a new session leader in that case, and run
107 // as part of the parent session. Otherwise, the new session cannot claim the
108 // terminal as a controlling terminal (it is already claimed), meaning that it
109 // will not see control signals from ^C etc.
112 // Disable suspend (^Z) (and on some systems, delayed suspend / ^Y)
113 signal(SIGTSTP, SIG_IGN);
115 // Become session leader
117 ioctl(0, TIOCSCTTY, 0);
120 tcsetpgrp(0, getpgrp());
123 if (uid != uid_t(-1)) {
124 if (setreuid(uid, uid) != 0) goto failure_out;
125 if (setregid(gid, gid) != 0) goto failure_out;
128 sigprocmask(SIG_SETMASK, &sigwait_set, nullptr);
130 execvp(args[0], const_cast<char **>(args));
132 // If we got here, the exec failed:
134 int exec_status = errno;
135 write(wpipefd, &exec_status, sizeof(int));