CAP_GRP(3)             FreeBSD Library Functions Manual             CAP_GRP(3)

NAME
     cap_getgrent, cap_getgrnam, cap_getgrgid, cap_getgrent_r, cap_getgrnam_r,
     cap_getgrgid_r, cap_setgroupent, cap_setgrent, cap_endgrent,
     cap_grp_limit_cmds, cap_grp_limit_fields, cap_grp_limit_groups - library
     for group database operations in capability mode

LIBRARY
     library "libcap_grp"

SYNOPSIS
     #include <sys/nv.h>
     #include <libcasper.h>
     #include <casper/cap_grp.h>

     struct group *
     cap_getgrent(cap_channel_t *chan);

     struct group *
     cap_getgrnam(cap_channel_t *chan, const char *name);

     struct group *
     cap_getgrgid(cap_channel_t *chan, gid_t gid);

     int
     cap_getgrent_r(cap_channel_t *chan, struct group *grp, char *buffer,
         size_t bufsize, struct group **result);

     int
     cap_getgrnam_r(cap_channel_t *chan, const char *name, struct group *grp,
         char *buffer, size_t bufsize, struct group **result);

     int
     cap_getgrgid_r(cap_channel_t *chan, gid_t gid, struct group *grp,
         char *buffer, size_t bufsize, struct group **result);

     int
     cap_setgroupent(cap_channel_t *chan, int stayopen);

     int
     cap_setgrent(cap_channel_t *chan);

     void
     cap_endgrent(cap_channel_t *chan);

     int
     cap_grp_limit_cmds(cap_channel_t *chan, const char * const *cmds,
         size_t ncmds);

     int
     cap_grp_limit_fields(cap_channel_t *chan, const char * const *fields,
         size_t nfields);

     int
     cap_grp_limit_groups(cap_channel_t *chan, const char * const *names,
         size_t nnames, const gid_t *gids, size_t ngids);

DESCRIPTION
     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.

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);

SEE ALSO
     cap_enter(2), endgrent(3), err(3), getgrent(3), getgrent_r(3),
     getgrgid(3), getgrgid_r(3), getgrnam(3), getgrnam_r(3), setgrent(3),
     setgroupent(3), capsicum(4), nv(9)

HISTORY
     The cap_grp service first appeared in FreeBSD 10.3.

AUTHORS
     The cap_grp service was implemented by Pawel Jakub Dawidek
     <pawel@dawidek.net> under sponsorship from the FreeBSD Foundation.

     This manual page was written by
     Mariusz Zaborski <oshogbo@FreeBSD.org>.

FreeBSD 13.1-RELEASE-p6           May 5, 2020          FreeBSD 13.1-RELEASE-p6