cap_grp_limit_groups3

Usage

Library

library “libcap_grp”

Overview

The functions cap_getgrent(), cap_getgrnam(), cap_getgrgid(), cap_getgrent_r(), cap_getgrnam_r(), cap_getgrgid_r(), cap_setgroupent(), cap_setgrent(), and cap_endgrent() are respectively equivalent to getgrent(3), getgrnam(3), getgrgid(3), getgrent_r(3), getgrnam_r(3), getgrgid_r(3), setgroupent(3), setgrent(3), and endgrent(3) except that the connection to the system.grp service needs to be provided.

The cap_grp_limit_cmds() function limits the functions allowed in the service. The cmds variable can be set to getgrent, getgrnam, getgrgid, getgrent_r, getgrnam_r, getgrgid_r, setgroupent, setgrent, or endgrent which will allow to use the function associated with the name. The ncmds variable contains the number of cmds provided.

The cap_grp_limit_fields() function allows limit fields returned in the structure group. The fields variable can be set to gr_name gr_passwd gr_gid or gr_mem. The field which was set as the limit will be returned, while the rest of the values not set this way will have default values. The nfields variable contains the number of fields provided.

The cap_grp_limit_groups() function allows to limit access to groups. The names variable allows to limit groups by name and the gids variable by the group number. The nnames and ngids variables provide numbers of limited names and gids.

All of these functions are reentrant but not thread-safe. That is, they may be called from separate threads only with different cap_channel_t arguments or with synchronization.

Examples

The following example first opens a capability to casper and then uses this capability to create the system.grp casper service and uses it to get a group name.

cap_channel_t *capcas, *capgrp;
const char *cmds[] = { "getgrgid" };
const char *fields[] = { "gr_name" };
const gid_t gid[] = { 1 };
struct group *group;
/* Open capability to Casper. */
capcas = cap_init();
if (capcas == NULL)
        err(1, "Unable to contact Casper");
/* Enter capability mode sandbox. */
if (cap_enter() < 0 && errno != ENOSYS)
        err(1, "Unable to enter capability mode");
/* Use Casper capability to create capability to the system.grp service. */
capgrp = cap_service_open(capcas, "system.grp");
if (capgrp == NULL)
        err(1, "Unable to open system.grp service");
/* Close Casper capability, we don't need it anymore. */
cap_close(capcas);
/* Limit service to one single function. */
if (cap_grp_limit_cmds(capgrp, cmds, nitems(cmds)))
	err(1, "Unable to limit access to system.grp service");
/* Limit service to one field as we only need name of the group. */
if (cap_grp_limit_fields(capgrp, fields, nitems(fields)))
	err(1, "Unable to limit access to system.grp service");
/* Limit service to one gid. */
if (cap_grp_limit_groups(capgrp, NULL, 0, gid, nitems(gid)))
	err(1, "Unable to limit access to system.grp service");
group = cap_getgrgid(capgrp, gid[0]);
if (group == NULL)
	err(1, "Unable to get name of group");
printf("GID %d is associated with name %s.\n", gid[0], group->gr_name);
cap_close(capgrp);