121 lines · c
1// SPDX-License-Identifier: GPL-2.02 3#define _GNU_SOURCE4#include <err.h>5#include <errno.h>6#include <fcntl.h>7#include <inttypes.h>8#include <limits.h>9#include <sched.h>10#include <signal.h>11#include <stdio.h>12#include <stdlib.h>13#include <string.h>14#include <sys/stat.h>15#include <sys/syscall.h>16#include <sys/types.h>17#include <sys/wait.h>18#include <unistd.h>19 20#ifndef CLONE_PIDFD21#define CLONE_PIDFD 0x0000100022#endif23 24#ifndef __NR_pidfd_send_signal25#define __NR_pidfd_send_signal -126#endif27 28static int do_child(void *args)29{30 printf("%d\n", getpid());31 _exit(EXIT_SUCCESS);32}33 34static pid_t pidfd_clone(int flags, int *pidfd)35{36 size_t stack_size = 1024;37 char *stack[1024] = { 0 };38 39#ifdef __ia64__40 return __clone2(do_child, stack, stack_size, flags | SIGCHLD, NULL, pidfd);41#else42 return clone(do_child, stack + stack_size, flags | SIGCHLD, NULL, pidfd);43#endif44}45 46static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,47 unsigned int flags)48{49 return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);50}51 52static int pidfd_metadata_fd(pid_t pid, int pidfd)53{54 int procfd, ret;55 char path[100];56 57 snprintf(path, sizeof(path), "/proc/%d", pid);58 procfd = open(path, O_DIRECTORY | O_RDONLY | O_CLOEXEC);59 if (procfd < 0) {60 warn("Failed to open %s\n", path);61 return -1;62 }63 64 /*65 * Verify that the pid has not been recycled and our /proc/<pid> handle66 * is still valid.67 */68 ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);69 if (ret < 0) {70 switch (errno) {71 case EPERM:72 /* Process exists, just not allowed to signal it. */73 break;74 default:75 warn("Failed to signal process\n");76 close(procfd);77 procfd = -1;78 }79 }80 81 return procfd;82}83 84int main(int argc, char *argv[])85{86 int pidfd = -1, ret = EXIT_FAILURE;87 char buf[4096] = { 0 };88 pid_t pid;89 int procfd, statusfd;90 ssize_t bytes;91 92 pid = pidfd_clone(CLONE_PIDFD, &pidfd);93 if (pid < 0)94 err(ret, "CLONE_PIDFD");95 if (pidfd == -1) {96 warnx("CLONE_PIDFD is not supported by the kernel");97 goto out;98 }99 100 procfd = pidfd_metadata_fd(pid, pidfd);101 close(pidfd);102 if (procfd < 0)103 goto out;104 105 statusfd = openat(procfd, "status", O_RDONLY | O_CLOEXEC);106 close(procfd);107 if (statusfd < 0)108 goto out;109 110 bytes = read(statusfd, buf, sizeof(buf));111 if (bytes > 0)112 bytes = write(STDOUT_FILENO, buf, bytes);113 close(statusfd);114 ret = EXIT_SUCCESS;115 116out:117 (void)wait(NULL);118 119 exit(ret);120}121