/* recvcred.c * * Send a file descriptor : */#include "common.h"/* * Receive Data & Credentials : * * ARGUMENTS: *  s       Socket to read from *  credp   Ptr to receiving area for cred. *  buf     Ptr to receiving buffer for data *  bufsiz  Maximum # of bytes for buffer *  addr    Ptr to buffer to receive peer *          address (or NULL) *  alen    Ptr to Maximum byte length *          (updated with actual length *          upon return.) * * RETURNS: *  >=0     Data bytes read *  -1      Failed: check errno * * NOTES: *  The value -1 is returned with errno set *  to ENOENT, if data is returned without *  any credentials. */intrecv_cred(  int s,                          /* Socket */  struct ucred *credp, /* Credential buffer */  void *buf,       /* Receiving Data buffer */  unsigned bufsiz,   /* Recv. Data buf size */  void *addr,      /* Received Peer address */  socklen_t *alen) {  /* Ptr to addr length */    int z;    struct msghdr msgh;   /* Message header */    struct iovec iov[1];      /* I/O vector */    struct cmsghdr *cmsgp = NULL;    char mbuf[CMSG_SPACE(sizeof *credp)];    /*     * Zero out message areas :     */    memset(&msgh,0,sizeof msgh);    memset(mbuf,0,sizeof mbuf);    /*     * Establish datagram address (if any) :     */    msgh.msg_name = addr;    msgh.msg_namelen = alen ? *alen : 0;    /*     * Point to our I/O vector of 1 element:     */    msgh.msg_iov = iov;    msgh.msg_iovlen = 1;    /*     * Initialize our 1 I/O element vector :     */    iov[0].iov_base = buf;    iov[0].iov_len = bufsiz;    /*     * Initialize control structure :     */    msgh.msg_control = mbuf;    msgh.msg_controllen = sizeof mbuf;    /*     * Receive a message :     */    do  {        z = recvmsg(s,&msgh,0);    } while ( z == -1 && errno == EINTR );    if ( z == -1 )        return -1;  /* Failed: check errno */    /*     * If ptr alen is non-NULL, return the     * returned address length (datagrams):     */    if ( alen )        *alen = msgh.msg_namelen;    /*     * Walk the list of control messages:     */    for ( cmsgp = CMSG_FIRSTHDR(&msgh);        cmsgp != NULL;        cmsgp = CMSG_NXTHDR(&msgh,cmsgp) ) {        if ( cmsgp->cmsg_level == SOL_SOCKET        && cmsgp->cmsg_type == SCM_CREDENTIALS ) {            /*             * Pass back credentials struct:             */            *credp = *                (struct ucred *) CMSG_DATA(cmsgp);            return z; /* # of data bytes read */        }    }    /*     * There were no credentials found. An error     * is returned here, since this applicaton     * insists on getting credentials.     */    errno = ENOENT;    return -1;}