| 1 | |
| 2 |
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| 3 | #define _GNU_SOURCE
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| 4 | #include <err.h>
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| 5 | #include <errno.h>
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| 6 | #include <fcntl.h>
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| 7 | #include <inttypes.h>
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| 8 | #include <limits.h>
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| 9 | #include <sched.h>
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| 10 | #include <signal.h>
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| 11 | #include <stdio.h>
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| 12 | #include <stdlib.h>
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| 13 | #include <string.h>
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| 14 | #include <sys/stat.h>
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| 15 | #include <sys/syscall.h>
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| 16 | #include <sys/types.h>
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| 17 | #include <sys/wait.h>
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| 18 | #include <unistd.h>
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| 19 |
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| 20 | #ifndef CLONE_PIDFD
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| 21 | #define CLONE_PIDFD 0x00001000
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| 22 | #endif
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| 23 |
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| 24 | #ifndef __NR_pidfd_send_signal
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| 25 | #define __NR_pidfd_send_signal -1
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| 26 | #endif
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| 27 |
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| 28 | static int do_child(void *args)
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| 29 | {
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| 30 | printf("%d\n", getpid());
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| 31 | _exit(EXIT_SUCCESS);
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| 32 | }
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| 33 |
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| 34 | static pid_t pidfd_clone(int flags, int *pidfd)
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| 35 | {
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| 36 | size_t stack_size = 1024;
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| 37 | char *stack[1024] = { 0 };
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| 38 |
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| 39 | #ifdef __ia64__
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| 40 | return __clone2(do_child, stack, stack_size, flags | SIGCHLD, NULL, pidfd);
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| 41 | #else
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| 42 | return clone(do_child, stack + stack_size, flags | SIGCHLD, NULL, pidfd);
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| 43 | #endif
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| 44 | }
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| 45 |
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| 46 | static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
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| 47 | unsigned int flags)
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| 48 | {
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| 49 | return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
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| 50 | }
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| 51 |
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| 52 | static int pidfd_metadata_fd(pid_t pid, int pidfd)
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| 53 | {
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| 54 | int procfd, ret;
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| 55 | char path[100];
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| 56 |
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| 57 | snprintf(path, sizeof(path), "/proc/%d", pid);
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| 58 | procfd = open(path, O_DIRECTORY | O_RDONLY | O_CLOEXEC);
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| 59 | if (procfd < 0) {
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| 60 | warn("Failed to open %s\n", path);
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| 61 | return -1;
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| 62 | }
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| 63 |
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| 64 | |
| 65 | * Verify that the pid has not been recycled and our /proc/<pid> handle
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| 66 | * is still valid.
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| 67 |
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| 68 | ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
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| 69 | if (ret < 0) {
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| 70 | switch (errno) {
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| 71 | case EPERM:
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| 72 |
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| 73 | break;
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| 74 | default:
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| 75 | warn("Failed to signal process\n");
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| 76 | close(procfd);
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| 77 | procfd = -1;
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| 78 | }
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| 79 | }
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| 80 |
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| 81 | return procfd;
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| 82 | }
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| 83 |
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| 84 | int main(int argc, char *argv[])
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| 85 | {
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| 86 | int pidfd = -1, ret = EXIT_FAILURE;
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| 87 | char buf[4096] = { 0 };
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| 88 | pid_t pid;
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| 89 | int procfd, statusfd;
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| 90 | ssize_t bytes;
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| 91 |
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| 92 | pid = pidfd_clone(CLONE_PIDFD, &pidfd);
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| 93 | if (pid < 0)
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| 94 | err(ret, "CLONE_PIDFD");
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| 95 | if (pidfd == -1) {
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| 96 | warnx("CLONE_PIDFD is not supported by the kernel");
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| 97 | goto out;
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| 98 | }
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| 99 |
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| 100 | procfd = pidfd_metadata_fd(pid, pidfd);
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| 101 | close(pidfd);
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| 102 | if (procfd < 0)
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| 103 | goto out;
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| 104 |
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| 105 | statusfd = openat(procfd, "status", O_RDONLY | O_CLOEXEC);
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| 106 | close(procfd);
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| 107 | if (statusfd < 0)
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| 108 | goto out;
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| 109 |
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| 110 | bytes = read(statusfd, buf, sizeof(buf));
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| 111 | if (bytes > 0)
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| 112 | bytes = write(STDOUT_FILENO, buf, bytes);
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| 113 | close(statusfd);
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| 114 | ret = EXIT_SUCCESS;
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| 115 |
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| 116 | out:
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| 117 | (void)wait(NULL);
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| 118 |
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| 119 | exit(ret);
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| 120 | }
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