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/* SPDX-License-Identifier: MIT */
/* SPDX-FileCopyrightText: (c) Copyright 2024 Andrew Bower <andrew@bower.uk> */
/* xchpst: eXtended Change Process State
* A tool that is backwards compatible with chpst(8) from runit(8),
* offering additional options to harden process with namespace isolation
* and more. */
#include <poll.h>
#include <signal.h>
#include <linux/prctl.h>
#include <sys/file.h>
#include <sys/pidfd.h>
#include <sys/signalfd.h>
#include <sys/wait.h>
#include "xchpst.h"
#include "join.h"
bool join(pid_t child, sigset_t *mask, sigset_t *oldmask, int *retcode) {
enum {
/* Offsets into poll set */
my_pidfd = 0,
my_signalfd = 1
};
struct signalfd_siginfo siginf;
siginfo_t pidinf;
int ready;
int sfd;
int pidfd;
int rc;
pidfd = pidfd_open(child, PIDFD_NONBLOCK);
if (pidfd == -1) {
perror("error setting up child supervision");
kill(child, SIGKILL);
return false;
}
sfd = signalfd(-1, mask, SFD_NONBLOCK);
if (sfd == -1) {
close(pidfd);
perror("error setting up signal proxy");
pidfd_send_signal(pidfd, SIGKILL, NULL, 0);
return false;
}
struct pollfd pollset[2] = {
[my_pidfd] = { .fd = pidfd, .events = POLLIN },
[my_signalfd] = { .fd = sfd, .events = POLLIN },
};
while(true) {
ready = poll(pollset, 2, -1);
if (ready == -1 && errno != EINTR) {
perror("poll");
} else if (ready != 0) {
if (pollset[my_pidfd].revents & POLLIN) {
/* Handle event on pidfd */
pidinf.si_pid = 0;
pidinf.si_signo = 0;
rc = waitid(P_PIDFD, pidfd, &pidinf, WEXITED | WNOHANG);
if (rc == -1) {
perror("waitid");
} else if (rc == 0 &&
pidinf.si_signo == SIGCHLD &&
pidinf.si_pid == child) {
if (pidinf.si_code == CLD_KILLED || pidinf.si_code == CLD_DUMPED) {
if (is_verbose())
fprintf(stderr, "child killed by signal %d\n", pidinf.si_status);
*retcode = 128 + pidinf.si_status;
} else if (pidinf.si_code == CLD_EXITED) {
*retcode = pidinf.si_code;
}
break;
} else {
fprintf(stderr, "got SIGCHLD from someone else's child (%d)!\n",
pidinf.si_pid);
}
}
if (pollset[my_signalfd].revents & POLLIN) {
/* Handle a signal received by parent process and pass to child */
rc = read(sfd, &siginf, sizeof siginf);
if (rc != sizeof siginf) {
perror("read signalfd");
break;
}
if (is_verbose())
fprintf(stderr, "passing on signal %d to child\n", siginf.ssi_signo);
pidfd_send_signal(pidfd, siginf.ssi_signo, NULL, 0);
}
}
}
if (is_verbose())
fprintf(stderr, "child terminated; cleaning up\n");
close(sfd);
close(pidfd);
sigprocmask(SIG_SETMASK, oldmask, NULL);
return true;
}
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