/*      $OpenBSD: pass.c,v 1.1.1.1 2018/04/10 23:00:53 bluhm Exp $      */
/*
 * Copyright (c) 2018 Alexander Bluhm <bluhm@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/socket.h>
#include <sys/wait.h>

#include <err.h>
#include <string.h>
#include <unistd.h>

#include "header.h"

void
fdops(int fdpre, int fdpost)
{
        struct msghdr    msg;
        struct iovec     iov[1];
        char             buf[1];
        struct cmsghdr  *cmsg;
        union {
                struct cmsghdr   hdr;
                unsigned char    buf[CMSG_SPACE(sizeof(int))];
        } cmsgbuf;
        pid_t child;
        int pair[2], status;

        if (socketpair(AF_UNIX, SOCK_DGRAM, 0, pair) == -1)
                err(1, "socketpair");

        memset(&msg, 0, sizeof(msg));
        msg.msg_control = &cmsgbuf.buf;
        msg.msg_controllen = sizeof(cmsgbuf.buf);

        if ((child = fork()) == -1)
                err(1, "fork");

        if (child == 0) {

                /* child process */

                cmsg = CMSG_FIRSTHDR(&msg);
                cmsg->cmsg_len = CMSG_LEN(sizeof(int));
                cmsg->cmsg_level = SOL_SOCKET;
                cmsg->cmsg_type = SCM_RIGHTS;

                *(int *)CMSG_DATA(cmsg) = fdpre;
                if (sendmsg(pair[1], &msg, 0) == -1)
                        err(1, "sendmsg pre");

                cmsg = CMSG_FIRSTHDR(&msg);
                cmsg->cmsg_len = CMSG_LEN(sizeof(int));
                cmsg->cmsg_level = SOL_SOCKET;
                cmsg->cmsg_type = SCM_RIGHTS;

                *(int *)CMSG_DATA(cmsg) = fdpost;
                if (sendmsg(pair[1], &msg, 0) == -1)
                        err(1, "sendmsg post");

                _exit(0);
        }

        /* parent process */

        msg.msg_iov = iov;
        msg.msg_iovlen = 1;
        iov[0].iov_base = buf;
        iov[0].iov_len = sizeof(buf);

        if (recvmsg(pair[0], &msg, 0) == -1)
                err(1, "recvmsg pre");
        if ((msg.msg_flags & MSG_TRUNC) || (msg.msg_flags & MSG_CTRUNC))
                errx(1, "trunk pre");

        if (recvmsg(pair[0], &msg, 0) == -1)
                err(1, "recvmsg post");
        if ((msg.msg_flags & MSG_TRUNC) || (msg.msg_flags & MSG_CTRUNC))
                errx(1, "trunk post");

        if (waitpid(child, &status, 0) == -1)
                err(1, "waitpid");
        if (status != 0)
                errx(1, "child failed: %d", status);
}