diff options
| -rw-r--r-- | src/init/s6-linux-init.c | 104 |
1 files changed, 52 insertions, 52 deletions
diff --git a/src/init/s6-linux-init.c b/src/init/s6-linux-init.c index e6b0d60..2cf3c09 100644 --- a/src/init/s6-linux-init.c +++ b/src/init/s6-linux-init.c @@ -120,75 +120,71 @@ static inline void run_stage2 (char const *basedir, char const **argv, unsigned /* This is ugly voodoo, keep away from innocent eyes. If ttyfd exists, it means we're in a "docker run -it" container or -equivalent, and ttyfd (a copy of the original stdin) is a ctty. We don't +equivalent, and tty (name of the original stdin) is a ctty. We don't want the supervision tree to have this ctty (else ^C kills everything) but we want stage 2 to keep it if possible, so that if we have a CMD run by stage 2 (as is the case with s6-overlay), it remains interactive, i.e. control sequences can be sent to it. - In order to achieve that, we have the child (future stage 2) steal the -ctty from the parent (future s6-svscan). But that may not work, for instance -in a USER container, where we don't have the appropriate permissions; in -which case the parent must be informed that the operation failed, so it can -relinquish the ctty itself - the child won't get the ctty but at least the -parent won't keep it. - Transmission of the information is done via a pipe, it's the simplest -way to properly order operations. - If the parent abandons its ctty itself, the child needs to protect against -the SIGHUP it receives when it happens. + We cannot have the child (future stage 2) steal the ctty from the parent +(future s6-svscan) via TIOCSCTTY because we may not have the permissions for +it: Docker containers don't give CAP_SYS_ADMIN to pid 1, and user containers +are a thing. + So instead, we have the parent relinquish the ctty, then the child reopen +it - which makes it a ctty for the child. This requires /dev/pts to be +pre-mounted, but that's usually the case. Even if it's not, the child doesn't +get its ctty, but at least the parent doesn't have it anymore. + Pipes are used for synchronization. */ -static inline pid_t fork_and_setup_session (int ttyfd) /* closes ttyfd */ +static inline pid_t fork_and_setup_session (char const *tty) { pid_t pid ; - if (ttyfd < 0) /* the common case is simple */ + if (!tty) { pid = fork() ; if (pid == -1) strerr_diefu1sys(111, "fork") ; setsid() ; } - else /* let the insanity begin */ + else { - int p[2] ; - if (pipe(p) == -1) strerr_diefu1sys(111, "pipe") ; + int p[2][2] ; + int r ; + char c ; + if (pipe(p[0]) == -1 || pipe(p[1])) strerr_diefu1sys(111, "pipe") ; pid = fork() ; if (pid == -1) strerr_diefu1sys(111, "fork") ; - if (!pid) - { /* child */ - PROG = "s6-linux-init (child)" ; - close(p[0]) ; - if (setsid() == -1) strerr_diefu1sys(111, "setsid") ; - if (fd_move(0, ttyfd) == -1) strerr_diefu1sys(111, "move stdin fd") ; - if (ioctl(0, TIOCSCTTY, 1) == -1) - { - strerr_warnwu1sys("grab controlling terminal") ; - if (!sig_altignore(SIGHUP)) - strerr_diefu1sys(111, "ignore SIGHUP") ; - if (write(p[1], "1", 1) < 1) /* '1' == problem */ - strerr_diefu1sys(111, "write to parent") ; - } - else if (write(p[1], "0", 1) < 1) /* '0' == ok */ - strerr_diefu1sys(111, "write to parent") ; - close(p[1]) ; + if (pid) + { + close(p[0][1]) ; + close(p[1][0]) ; + r = read(p[0][0], &c, 1) ; + if (r == -1) strerr_diefu2sys(111, "read from ", "child") ; + if (!r) strerr_dief2x(111, "child", " died") ; + close(p[0][0]) ; + if (ioctl(1, TIOCNOTTY) == -1) strerr_warnwu1sys("relinquish controlling terminal") ; + if (write(p[1][1], "", 1) < 1) strerr_diefu2sys(111, "write to ", "child") ; + close(p[1][1]) ; } else - { /* parent */ - int r ; - char c ; - close(p[1]) ; - r = read(p[0], &c, 1) ; - if (r == -1) - strerr_diefu1sys(111, "read from child") ; - else if (!r) - strerr_dief1x(111, "child died") ; - else if (c == '1') + { + int fd ; + PROG = "s6-linux-init (child)" ; + close(p[1][1]) ; + close(p[0][0]) ; + if (setsid() == -1) strerr_diefu1sys(111, "setsid") ; + if (write(p[0][1], "", 1) < 1) strerr_diefu2sys(111, "write to ", "parent") ; + close(p[0][1]) ; + r = read(p[1][0], &c, 1) ; + if (r == -1) strerr_diefu2sys(111, "read from ", "parent") ; + if (!r) strerr_dief2x(111, "parent", " died") ; + close(p[1][0]) ; + fd = openb_read(tty) ; + if (fd == -1) strerr_warnwu2sys("open ", tty) ; + else if (fd_move(0, fd) == -1) { - if (ioctl(ttyfd, TIOCNOTTY) == -1) - strerr_warnwu1sys("relinquish controlling terminal") ; + strerr_warnwu3sys("make ", tty, " into new stdin") ; + close(fd) ; } - else if (c != '0') - strerr_dief1x(100, "bad parent/child protocol") ; - close(p[0]) ; - close(ttyfd) ; } } return pid ; @@ -204,7 +200,7 @@ int main (int argc, char const **argv, char const *const *envp) char const *initdefault = "default" ; int mounttype = 1 ; int hasconsole = 1 ; - int ttyfd = -1 ; + char *tty = 0 ; stralloc envmodifs = STRALLOC_ZERO ; PROG = "s6-linux-init" ; @@ -252,7 +248,11 @@ int main (int argc, char const **argv, char const *const *envp) if (r) strerr_warnw1x("parent wrote to fd 3!") ; close(3) ; } - if (isatty(0) && !slashdev) ttyfd = dup(0) ; + if (!slashdev && hasconsole && isatty(1)) + { + tty = ttyname(1) ; + if (!tty) strerr_warnwu1sys("ttyname stdout") ; + } } else if (hasconsole) allwrite(1, BANNER, sizeof(BANNER) - 1) ; if (chdir("/") == -1) strerr_diefu1sys(111, "chdir to /") ; @@ -347,7 +347,7 @@ int main (int argc, char const **argv, char const *const *envp) newenvp[0] = pathvar ; } if (nologger && pipe(notifpipe) < 0) strerr_diefu1sys(111, "pipe") ; - if (!fork_and_setup_session(ttyfd)) + if (!fork_and_setup_session(tty)) run_stage2(basedir, argv, argc, newenvp, !!path, envmodifs.s, envmodifs.len, initdefault) ; if (nologger) { |