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#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <stdbool.h>
#include <sys/epoll.h>
#include <wait.h>
#define SEND_CREDS_OK 0
#define SEND_CREDS_NOTSK 1
#define SEND_CREDS_FAIL 2
static bool recv_creds(int sock, struct ucred *cred, char *v);
static int wait_for_pid(pid_t pid);
static int send_creds(int sock, struct ucred *cred, char v, bool pingfirst);
static int send_creds_clone_wrapper(void *arg);
static int send_creds_clone_wrapper(void *arg)
{
struct ucred cred;
char v;
int sock = *(int*)arg;
cred.uid = 0;
cred.gid = 0;
cred.pid = 1;
v = '1';
if (send_creds(sock, &cred, v, true) != SEND_CREDS_OK)
return 1;
return 0;
}
static int wait_for_pid(pid_t pid)
{
int status, ret;
if (pid < 0)
return -1;
again:
ret = waitpid(pid, &status, 0);
if (ret == -1) {
if (errno = EINTR)
goto again;
return -1;
}
if (ret != pid)
goto again;
if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
return -1;
return 0;
}
/*
* clone a task which switches to @task's namespace and writes '1'.
* over a unix sock so we can read the task's reaper's pid in our
* namespace
*
* Note: glibc's fork() does not respect pidns, which can lead to failed
* assertions inside glibc (and thus failed forks) if the child's pid in
* the pidns and the parent pid outside are identical. Using clone prevents
* this issue.
*/
static void write_task_init_pid_exit(int sock, pid_t target)
{
char fnam[100];
pid_t pid;
int fd, ret;
size_t stack_size = sysconf(_SC_PAGESIZE);
void *stack = alloca(stack_size);
ret = snprintf(fnam, sizeof(fnam), "/proc/%d/ns/pid", (int)target);
if (ret < 0 || ret >= sizeof(fnam))
_exit(1);
fd = open(fnam, O_RDONLY);
if (fd < 0) {
perror("write_task_init_pid_exit open of ns/pid" );
_exit(1);
}
if (setns(fd, 0)) {
perror("write_task_init_pid_exit setns 1");
close(fd);
_exit(1);
}
pid = clone(send_creds_clone_wrapper, stack+stack_size, SIGCHLD, &sock);
if (pid < 0)
_exit(1);
if (pid != 0) {
if (!wait_for_pid(pid))
_exit(1);
_exit(0);
}
}
static pid_t get_init_pid_for_task(pid_t task)
{
int sock[2];
pid_t pid;
pid_t ret = -1;
char v = '0';
struct ucred cred;
if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sock) < 0 ) {
perror("socketpair");
return -1;
}
pid = fork();
if (pid < 0)
goto out;
if (!pid) {
// Child process
close(sock[1]);
write_task_init_pid_exit(sock[0], task);
_exit(0);
}
if (!recv_creds(sock[1], &cred, &v))
goto out;
ret = cred.pid;
out:
close(sock[0]);
close(sock[1]);
if (pid > 0)
wait_for_pid(pid);
return ret;
}
void usage(int argc, char **argv)
{
printf("Usage:\n");
printf("\t%s pid\n", argv[1]);
}
int main(int argc, char **argv)
{
pid_t result;
pid_t target;
if (argc != 2) {
usage(argc, argv);
exit(0);
}
target = (pid_t)atoi(argv[1]);
result = get_init_pid_for_task(target);
printf("pid %d 's init pid is %d\n", (int)target, (int)result);
}
#define POLLIN_SET ( EPOLLIN | EPOLLHUP | EPOLLRDHUP )
static bool wait_for_sock(int sock, int timeout)
{
struct epoll_event ev;
int epfd, ret, now, starttime, deltatime, saved_errno;
if ((starttime = time(NULL)) < 0)
return false;
if ((epfd = epoll_create(1)) < 0) {
printf("%s\n", "Failed to create epoll socket: %m.");
return false;
}
ev.events = POLLIN_SET;
ev.data.fd = sock;
if (epoll_ctl(epfd, EPOLL_CTL_ADD, sock, &ev) < 0) {
printf("%s\n", "Failed adding socket to epoll: %m.");
close(epfd);
return false;
}
again:
if ((now = time(NULL)) < 0) {
close(epfd);
return false;
}
deltatime = (starttime + timeout) - now;
if (deltatime < 0) { // timeout
errno = 0;
close(epfd);
return false;
}
ret = epoll_wait(epfd, &ev, 1, 1000*deltatime + 1);
if (ret < 0 && errno == EINTR)
goto again;
saved_errno = errno;
close(epfd);
if (ret <= 0) {
errno = saved_errno;
return false;
}
return true;
}
static int msgrecv(int sockfd, void *buf, size_t len)
{
if (!wait_for_sock(sockfd, 2))
return -1;
return recv(sockfd, buf, len, MSG_DONTWAIT);
}
static int send_creds(int sock, struct ucred *cred, char v, bool pingfirst)
{
struct msghdr msg = { 0 };
struct iovec iov;
struct cmsghdr *cmsg;
char cmsgbuf[CMSG_SPACE(sizeof(*cred))];
char buf[1];
buf[0] = 'p';
if (pingfirst) {
if (msgrecv(sock, buf, 1) != 1) {
printf("%s\n", "Error getting reply from server over socketpair.");
return SEND_CREDS_FAIL;
}
}
msg.msg_control = cmsgbuf;
msg.msg_controllen = sizeof(cmsgbuf);
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_len = CMSG_LEN(sizeof(struct ucred));
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_CREDENTIALS;
memcpy(CMSG_DATA(cmsg), cred, sizeof(*cred));
msg.msg_name = NULL;
msg.msg_namelen = 0;
buf[0] = v;
iov.iov_base = buf;
iov.iov_len = sizeof(buf);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
if (sendmsg(sock, &msg, 0) < 0) {
printf("Failed at sendmsg: %s.\n",strerror(errno));
if (errno == 3)
return SEND_CREDS_NOTSK;
return SEND_CREDS_FAIL;
}
return SEND_CREDS_OK;
}
static bool recv_creds(int sock, struct ucred *cred, char *v)
{
struct msghdr msg = { 0 };
struct iovec iov;
struct cmsghdr *cmsg;
char cmsgbuf[CMSG_SPACE(sizeof(*cred))];
char buf[1];
int ret;
int optval = 1;
*v = '1';
cred->pid = -1;
cred->uid = -1;
cred->gid = -1;
if (setsockopt(sock, SOL_SOCKET, SO_PASSCRED, &optval, sizeof(optval)) == -1) {
printf("Failed to set passcred: %s\n", strerror(errno));
return false;
}
buf[0] = '1';
if (write(sock, buf, 1) != 1) {
printf("Failed to start write on scm fd: %s\n", strerror(errno));
return false;
}
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_control = cmsgbuf;
msg.msg_controllen = sizeof(cmsgbuf);
iov.iov_base = buf;
iov.iov_len = sizeof(buf);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
if (!wait_for_sock(sock, 2)) {
printf("Timed out waiting for scm_cred: %s\n", strerror(errno));
return false;
}
ret = recvmsg(sock, &msg, MSG_DONTWAIT);
if (ret < 0) {
printf("Failed to receive scm_cred: %s\n", strerror(errno));
return false;
}
cmsg = CMSG_FIRSTHDR(&msg);
if (cmsg && cmsg->cmsg_len == CMSG_LEN(sizeof(struct ucred)) &&
cmsg->cmsg_level == SOL_SOCKET &&
cmsg->cmsg_type == SCM_CREDENTIALS) {
memcpy(cred, CMSG_DATA(cmsg), sizeof(*cred));
}
*v = buf[0];
return true;
}
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