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CAP_PWD(3) Library Functions Manual CAP_PWD(3)

cap_getpwent, cap_getpwnam, cap_getpwuid, cap_getpwent_r, cap_getpwnam_r, cap_getpwuid_r, cap_setpassent, cap_setpwent, cap_endpwent, cap_pwd_limit_cmds, cap_pwd_limit_fields, cap_pwd_limit_users — library for password database operations in capability mode

library “libcap_pwd”

#include <libcasper.h>
#include <casper/cap_pwd.h>

struct passwd *
cap_getpwent(cap_channel_t *chan);

struct passwd *
cap_getpwnam(cap_channel_t *chan, const char *login);

struct passwd *
cap_getpwuid(cap_channel_t *chan, uid_t uid);

int
cap_getpwent_r(cap_channel_t *chan, struct passwd *pwd, char *buffer, size_t bufsize, struct passwd **result);

int
cap_getpwnam_r(cap_channel_t *chan, const char *name, struct passwd *pwd, char *buffer, size_t bufsize, struct passwd **result);

int
cap_getpwuid_r(cap_channel_t *chan, uid_t uid, struct passwd *pwd, char *buffer, size_t bufsize, struct passwd **result);

int
cap_setpassent(cap_channel_t *chan, int stayopen);

void
cap_setpwent(cap_channel_t *chan);

void
cap_endpwent(cap_channel_t *chan);

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

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

int
cap_pwd_limit_users(cap_channel_t *chan, const char * const *names, size_t nnames, uid_t *uids, size_t nuids);

The functions (), (), (), (), (), (), (), (), and () are respectively equivalent to getpwent(3), getpwnam(3), getpwuid(3), getpwent_r(3), getpwnam_r(3), getpwuid_r(3), setpassent(3), setpwent(3), and cap_endpwent(3) except that the connection to the system.pwd service needs to be provided.

The () function limits the functions allowed in the service. The cmds variable can be set to getpwent, getpwnam, getpwuid, getpwent_r, getpwnam_r, getpwuid_r, setpassent, setpwent, or endpwent which will allow to use the function associated with the name. The ncmds variable contains the number of cmds provided.

The () function allows limit fields returned in the structure passwd. The fields variable can be set to pw_name, pw_passwd, pw_uid, pw_gid, pw_change, pw_class, pw_gecos, pw_dir, pw_shell, pw_expire or pw_fields 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 () function allows to limit access to users. The names variable allows to limit users by name and the uids variable by the user number. The nnames and nuids variables provide numbers of limited names and uids.

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

cap_channel_t *capcas, *cappwd;
const char *cmds[] = { "getpwuid" };
const char *fields[] = { "pw_name" };
uid_t uid[] = { 1 };
struct passwd *passwd;

/* 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.pwd service. */
cappwd = cap_service_open(capcas, "system.pwd");
if (cappwd == NULL)
        err(1, "Unable to open system.pwd service");

/* Close Casper capability, we don't need it anymore. */
cap_close(capcas);

/* Limit service to one single function. */
if (cap_pwd_limit_cmds(cappwd, cmds, nitems(cmds)))
	err(1, "Unable to limit access to system.pwd service");

/* Limit service to one field as we only need name of the user. */
if (cap_pwd_limit_fields(cappwd, fields, nitems(fields)))
	err(1, "Unable to limit access to system.pwd service");

/* Limit service to one uid. */
if (cap_pwd_limit_users(cappwd, NULL, 0, uid, nitems(uid)))
	err(1, "Unable to limit access to system.pwd service");

passwd = cap_getpwuid(cappwd, uid[0]);
if (passwd == NULL)
	err(1, "Unable to get name of user");

printf("UID %d is associated with name %s.\n", uid[0], passwd->pw_name);

cap_close(cappwd);

cap_enter(2), endpwent(3), err(3), getpwent(3), getpwent_r(3), getpwnam(3), getpwnam_r(3), getpwuid(3), getpwuid_r(3), setpassent(3), setpwent(3), capsicum(4), nv(9)

The cap_pwd 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>.

June 20, 2018 FreeBSD-12.0