uvms/pkgs/ch-proxy/sendfd.c

#include "sendfd.h"
#include "sys/socket.h" /* cmsghdr */
#include "stdio.h" /* perror */


ssize_t send_fd(int dst_fd, int fd, const struct iovec *iov) {
    struct msghdr msg = { 0 };

    /* openssh expects to receive a dummy length=1 iovec? */
    char ch = 0;
    struct iovec vecDefault = { 0 };
    vecDefault.iov_base = &ch;
    vecDefault.iov_len = 1;
    msg.msg_iov = iov == NULL ? &vecDefault : iov;
    msg.msg_iovlen = 1;

    union {
        struct cmsghdr align;
        char buf[CMSG_SPACE(sizeof(int))];
    } u;

    msg.msg_control = u.buf;
    msg.msg_controllen = sizeof(u.buf);

    struct cmsghdr *cmptr;
    cmptr = CMSG_FIRSTHDR(&msg);

    if (cmptr == NULL) {
        perror("ch-proxy/send_fd/CMSG_FIRSTHDR: failed to initialize msg_control\n");
    }

    cmptr->cmsg_len = CMSG_LEN(sizeof(int));
    cmptr->cmsg_level = SOL_SOCKET;
    cmptr->cmsg_type = SCM_RIGHTS;
    *((int*) CMSG_DATA(cmptr)) = fd;

    return (sendmsg(dst_fd, &msg, 0));
}

int recv_fd(int sock, int flags) {
    int out = -1;

    struct msghdr msg = { 0 };
    struct cmsghdr *cmsg = NULL;
    struct iovec iov = { 0 };
    char dummy = 0;

    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;

    iov.iov_base = &dummy;
    iov.iov_len = sizeof(dummy);

    union {
        struct cmsghdr align;
        char buf[CMSG_SPACE(sizeof(int))];
    } u;

    msg.msg_control = u.buf;
    msg.msg_controllen = sizeof(u.buf);

    int bytes = 0;
    if ((bytes = recvmsg(sock, &msg, flags)) < 0) {
        perror("recv_fd: recvmsg");
        return -1;
    }
    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
        if (cmsg->cmsg_level != SOL_SOCKET) { continue; }
        if (cmsg->cmsg_type != SCM_RIGHTS) { continue; }
        if (CMSG_LEN(cmsg) < sizeof(out)) { continue; }
        out = *(int*)CMSG_DATA(cmsg);
    }
    return out;
}