/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2015.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* Listing 9-1 */

/* idshow.c

   Display all user and group identifiers associated with a process.

   Note: This program uses Linux-specific calls and the Linux-specific
   file-system user and group IDs.
*/
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/fsuid.h>
#include <limits.h>
#include "ugid_functions.h"   /* userNameFromId() & groupNameFromId() */
#include "tlpi_hdr.h"

#define SG_SIZE (NGROUPS_MAX + 1)

int
main(int argc, char *argv[])
{
    uid_t ruid, euid, suid, fsuid;
    gid_t rgid, egid, sgid, fsgid;
    gid_t suppGroups[SG_SIZE];
    int numGroups, j;
    char *p;

    if (getresuid(&ruid, &euid, &suid) == -1)
        errExit("getresuid");
    if (getresgid(&rgid, &egid, &sgid) == -1)
        errExit("getresgid");

    /* Attempts to change the file-system IDs are always ignored
       for unprivileged processes, but even so, the following
       calls return the current file-system IDs */

    fsuid = setfsuid(0);
    fsgid = setfsgid(0);

    printf("UID: ");
    p = userNameFromId(ruid);
    printf("real=%s (%ld); ", (p == NULL) ? "???" : p, (long) ruid);
    p = userNameFromId(euid);
    printf("eff=%s (%ld); ", (p == NULL) ? "???" : p, (long) euid);
    p = userNameFromId(suid);
    printf("saved=%s (%ld); ", (p == NULL) ? "???" : p, (long) suid);
    p = userNameFromId(fsuid);
    printf("fs=%s (%ld); ", (p == NULL) ? "???" : p, (long) fsuid);
    printf("\n");

    printf("GID: ");
    p = groupNameFromId(rgid);
    printf("real=%s (%ld); ", (p == NULL) ? "???" : p, (long) rgid);
    p = groupNameFromId(egid);
    printf("eff=%s (%ld); ", (p == NULL) ? "???" : p, (long) egid);
    p = groupNameFromId(sgid);
    printf("saved=%s (%ld); ", (p == NULL) ? "???" : p, (long) sgid);
    p = groupNameFromId(fsgid);
    printf("fs=%s (%ld); ", (p == NULL) ? "???" : p, (long) fsgid);
    printf("\n");

    numGroups = getgroups(SG_SIZE, suppGroups);
    if (numGroups == -1)
        errExit("getgroups");

    printf("Supplementary groups (%d): ", numGroups);
    for (j = 0; j < numGroups; j++) {
        p = groupNameFromId(suppGroups[j]);
        printf("%s (%ld) ", (p == NULL) ? "???" : p, (long) suppGroups[j]);
    }
    printf("\n");

    exit(EXIT_SUCCESS);
}