Advanced Programming in the UNIX® Environment

ptg10805159

650 Advanced IPC Chapter 17

msg.msg_name = NULL;

msg.msg_namelen = 0;

msg.msg_flags = 0;

if (fd_to_send < 0) {

msg.msg_control = NULL;

msg.msg_controllen = 0;

buf[1] = -fd_to_send; /* nonzero status means error */

if (buf[1] == 0)

buf[1] = 1; /* -256, etc. would screw up protocol */

}else {

if (cmptr == NULL && (cmptr = malloc(CONTROLLEN)) == NULL)

return(-1);

msg.msg_control = cmptr;

msg.msg_controllen = CONTROLLEN;

cmp = cmptr;

cmp->cmsg_level = SOL_SOCKET;

cmp->cmsg_type = SCM_RIGHTS;

cmp->cmsg_len = RIGHTSLEN;

*(int *)CMSG_DATA(cmp) = fd_to_send; /* the fd to pass */

cmp = CMSG_NXTHDR(&msg, cmp);

cmp->cmsg_level = SOL_SOCKET;

cmp->cmsg_type = SCM_CREDTYPE;

cmp->cmsg_len = CREDSLEN;

credp = (struct CREDSTRUCT *)CMSG_DATA(cmp);

#if defined(SCM_CREDENTIALS)

credp->uid = geteuid();

credp->gid = getegid();

credp->pid = getpid();

#endif

buf[1] = 0; /* zero status means OK */

}

buf[0] = 0; /* null byte flag to recv_ufd() */

if (sendmsg(fd, &msg, 0) != 2)

return(-1);

return(0);

}

Figure 17.15 Sending credentials over UNIX domain sockets

Note that we need to initialize the credentials structureonly on Linux.

The function in Figure17.16 is a modified version ofrecv_fd,calledrecv_ufd,

that returns the user ID of the sender through a reference parameter.

#include "apue.h"

#include <sys/socket.h> /* struct msghdr */

#include <sys/un.h>

#if defined(SCM_CREDS) /* BSD interface */

#define CREDSTRUCT cmsgcred

#define CR_UID cmcred_uid

#define SCM_CREDTYPE SCM_CREDS

#elif defined(SCM_CREDENTIALS) /* Linux interface */