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Simplify signal handling using sigwait, eliminate some undefined behavior #72

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merged 1 commit into from
Apr 30, 2016
Merged

Simplify signal handling using sigwait, eliminate some undefined behavior #72

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97 changes: 43 additions & 54 deletions dumb-init.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,12 +35,8 @@ char debug = 0;
char use_setsid = 1;

void forward_signal(int signum) {
if (child_pid > 0) {
kill(use_setsid ? -child_pid : child_pid, signum);
DEBUG("Forwarded signal %d to children.\n", signum);
} else {
DEBUG("Didn't forward signal %d, no children exist yet.\n", signum);
}
kill(use_setsid ? -child_pid : child_pid, signum);
DEBUG("Forwarded signal %d to children.\n", signum);
}

/*
Expand Down Expand Up @@ -78,8 +74,26 @@ void forward_signal(int signum) {
*/
void handle_signal(int signum) {
DEBUG("Received signal %d.\n", signum);
if (signum == SIGCHLD) {
int status, exit_status;
pid_t killed_pid;
while ((killed_pid = waitpid(-1, &status, WNOHANG)) > 0) {
if (WIFEXITED(status)) {
exit_status = WEXITSTATUS(status);
DEBUG("A child with PID %d exited with exit status %d.\n", killed_pid, exit_status);
} else {
assert(WIFSIGNALED(status));
exit_status = 128 + WTERMSIG(status);
DEBUG("A child with PID %d was terminated by signal %d.\n", killed_pid, exit_status - 128);
}

if (
if (killed_pid == child_pid) {
forward_signal(SIGTERM); // send SIGTERM to any remaining children
DEBUG("Child exited with status %d. Goodbye.\n", exit_status);
exit(exit_status);
}
}
} else if (
signum == SIGTSTP || // tty: background yourself
signum == SIGTTIN || // tty: stop reading
signum == SIGTTOU // tty: stop writing
Expand Down Expand Up @@ -121,9 +135,9 @@ void print_help(char *argv[]) {
);
}

int main(int argc, char *argv[]) {
int signum, opt;

char **parse_command(int argc, char *argv[]) {
int opt;
struct option long_options[] = {
{"help", no_argument, NULL, 'h'},
{"single-child", no_argument, NULL, 'c'},
Expand All @@ -134,18 +148,18 @@ int main(int argc, char *argv[]) {
switch (opt) {
case 'h':
print_help(argv);
return 0;
exit(0);
case 'v':
debug = 1;
break;
case 'V':
fprintf(stderr, "dumb-init v%s", VERSION);
return 0;
exit(0);
case 'c':
use_setsid = 0;
break;
default:
return 1;
exit(1);
}
}

Expand All @@ -156,9 +170,8 @@ int main(int argc, char *argv[]) {
"Try %s --help for full usage.\n",
argv[0], argv[0]
);
return 1;
exit(1);
}
char **cmd = &argv[optind];

char *debug_env = getenv("DUMB_INIT_DEBUG");
if (debug_env && strcmp(debug_env, "1") == 0) {
Expand All @@ -172,29 +185,20 @@ int main(int argc, char *argv[]) {
DEBUG("Not running in setsid mode.\n");
}

/* register signal handlers */
for (signum = 1; signum < 32; signum++) {
if (signum == SIGKILL || signum == SIGSTOP || signum == SIGCHLD)
continue;
return &argv[optind];
}

if (signal(signum, handle_signal) == SIG_ERR) {
PRINTERR("Couldn't register signal handler for signal `%d`. Exiting.\n", signum);
return 1;
}
}
int main(int argc, char *argv[]) {
char **cmd = parse_command(argc, argv);

/* launch our process */
child_pid = fork();

if (child_pid < 0) {
PRINTERR("Unable to fork. Exiting.\n");
return 1;
}

if (child_pid == 0) {
} else if (child_pid == 0) {
/* child */
if (use_setsid) {
pid_t result = setsid();
if (result == -1) {
if (setsid() == -1) {
PRINTERR(
"Unable to setsid (errno=%d %s). Exiting.\n",
errno,
Expand All @@ -204,37 +208,22 @@ int main(int argc, char *argv[]) {
}
DEBUG("setsid complete.\n");
}

execvp(cmd[0], &cmd[0]);

// if this point is reached, exec failed, so we should exit nonzero
PRINTERR("%s: %s\n", argv[1], strerror(errno));
exit(2);
return 2;
} else {
pid_t killed_pid;
int exit_status, status;
/* parent */
int signum;
sigset_t all_signals;
sigfillset(&all_signals);
sigprocmask(SIG_BLOCK, &all_signals, NULL);

DEBUG("Child spawned with PID %d.\n", child_pid);

while ((killed_pid = waitpid(-1, &status, 0))) {
if (WIFEXITED(status)) {
exit_status = WEXITSTATUS(status);
DEBUG("A child with PID %d exited with exit status %d.\n", killed_pid, exit_status);
} else {
assert(WIFSIGNALED(status));
exit_status = 128 + WTERMSIG(status);
DEBUG("A child with PID %d was terminated by signal %d.\n", killed_pid, exit_status - 128);
}

if (killed_pid == child_pid) {
// send SIGTERM to any remaining children
forward_signal(SIGTERM);

DEBUG("Child exited with status %d. Goodbye.\n", exit_status);
exit(exit_status);
}
for (;;) {
sigwait(&all_signals, &signum);
handle_signal(signum);
}
}

return 0;
}
2 changes: 2 additions & 0 deletions tests/cli_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,7 @@ def test_verbose(flag):
(
b'^\[dumb-init\] Child spawned with PID [0-9]+\.\n'
b'\[dumb-init\] setsid complete\.\n'
b'\[dumb-init\] Received signal 17\.\n'
b'\[dumb-init\] A child with PID [0-9]+ exited with exit status 0.\n'
b'\[dumb-init\] Forwarded signal 15 to children\.\n'
b'\[dumb-init\] Child exited with status 0\. Goodbye\.\n$'
Expand All @@ -88,6 +89,7 @@ def test_verbose_and_single_child(flag1, flag2):
assert re.match(
(
b'^\[dumb-init\] Child spawned with PID [0-9]+\.\n'
b'\[dumb-init\] Received signal 17\.\n'
b'\[dumb-init\] A child with PID [0-9]+ exited with exit status 0.\n'
b'\[dumb-init\] Forwarded signal 15 to children\.\n'
b'\[dumb-init\] Child exited with status 0\. Goodbye\.\n$'
Expand Down