readcred.c

#include	"unp.h"

#define	CONTROL_LEN	(sizeof(struct cmsghdr) + sizeof(struct cmsgcred))

ssize_t
read_cred(int fd, void *ptr, size_t nbytes, struct cmsgcred *cmsgcredptr)
{
	struct msghdr	msg;
	struct iovec	iov[1];
	char			control[CONTROL_LEN];
	int				n;

	msg.msg_name = NULL;
	msg.msg_namelen = 0;
	iov[0].iov_base = ptr;
	iov[0].iov_len = nbytes;
	msg.msg_iov = iov;
	msg.msg_iovlen = 1;
	msg.msg_control = control;
	msg.msg_controllen = sizeof(control);
	msg.msg_flags = 0;

	if ( (n = recvmsg(fd, &msg, 0)) < 0)
		return(n);

	cmsgcredptr->cmcred_ngroups = 0;	/* indicates no credentials returned */
	if (cmsgcredptr && msg.msg_controllen > 0) {
		struct cmsghdr	*cmptr = (struct cmsghdr *) control;

		if (cmptr->cmsg_len < CONTROL_LEN)
			err_quit("control length = %d", cmptr->cmsg_len);
		if (cmptr->cmsg_level != SOL_SOCKET)
			err_quit("control level != SOL_SOCKET");
		if (cmptr->cmsg_type != SCM_CREDS)
			err_quit("control type != SCM_CREDS");
		memcpy(cmsgcredptr, CMSG_DATA(cmptr), sizeof(struct cmsgcred));
	}

	return(n);
}