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