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/*
* $Id$
*
* This file provides two functions:
* pam_modutil_drop_priv:
* temporarily lower process fs privileges by switching to another uid/gid,
* pam_modutil_regain_priv:
* regain process fs privileges lowered by pam_modutil_drop_priv().
*/
#include "pam_modutil_private.h"
#include <security/pam_ext.h>
#include <unistd.h>
#include <syslog.h>
#include <pwd.h>
#include <grp.h>
#include <sys/fsuid.h>
/*
* Two setfsuid() calls in a row are necessary to check
* whether setfsuid() succeeded or not.
*/
static int change_uid(uid_t uid, uid_t *save)
{
uid_t tmp = setfsuid(uid);
if (save)
*save = tmp;
return (uid_t) setfsuid(uid) == uid ? 0 : -1;
}
static int change_gid(gid_t gid, gid_t *save)
{
gid_t tmp = setfsgid(gid);
if (save)
*save = tmp;
return (gid_t) setfsgid(gid) == gid ? 0 : -1;
}
static int cleanup(struct pam_modutil_privs *p)
{
if (p->allocated) {
p->allocated = 0;
free(p->grplist);
}
p->grplist = NULL;
p->number_of_groups = 0;
return -1;
}
#define PRIV_MAGIC 0x1004000a
#define PRIV_MAGIC_DONOTHING 0xdead000a
int pam_modutil_drop_priv(pam_handle_t *pamh,
struct pam_modutil_privs *p,
const struct passwd *pw)
{
int res;
if (p->is_dropped) {
pam_syslog(pamh, LOG_CRIT,
"pam_modutil_drop_priv: called with dropped privileges");
return -1;
}
/*
* If not root, we can do nothing.
* If switching to root, we have nothing to do.
* That is, in both cases, we do not care.
*/
if (geteuid() != 0 || pw->pw_uid == 0) {
p->is_dropped = PRIV_MAGIC_DONOTHING;
return 0;
}
if (!p->grplist || p->number_of_groups <= 0) {
pam_syslog(pamh, LOG_CRIT,
"pam_modutil_drop_priv: called without room for supplementary groups");
return -1;
}
res = getgroups(0, NULL);
if (res < 0) {
pam_syslog(pamh, LOG_ERR,
"pam_modutil_drop_priv: getgroups failed: %m");
return -1;
}
p->allocated = 0;
if (res > p->number_of_groups) {
p->grplist = calloc(res, sizeof(gid_t));
if (!p->grplist) {
pam_syslog(pamh, LOG_CRIT, "out of memory");
return cleanup(p);
}
p->allocated = 1;
p->number_of_groups = res;
}
res = getgroups(p->number_of_groups, p->grplist);
if (res < 0) {
pam_syslog(pamh, LOG_ERR,
"pam_modutil_drop_priv: getgroups failed: %m");
return cleanup(p);
}
p->number_of_groups = res;
/*
* We should care to leave process credentials in consistent state.
* That is, e.g. if change_gid() succeeded but change_uid() failed,
* we should try to restore old gid.
*
* We try to add the supplementary groups on a best-effort
* basis. If it fails, it's not fatal: we fall back to using an
* empty list.
*/
if (initgroups(pw->pw_name, pw->pw_gid)) {
pam_syslog(pamh, LOG_WARNING,
"pam_modutil_drop_priv: initgroups failed: %m");
if (setgroups(0, NULL)) {
pam_syslog(pamh, LOG_ERR,
"pam_modutil_drop_priv: setgroups failed: %m");
return cleanup(p);
}
}
if (change_gid(pw->pw_gid, &p->old_gid)) {
pam_syslog(pamh, LOG_ERR,
"pam_modutil_drop_priv: change_gid failed: %m");
(void) setgroups(p->number_of_groups, p->grplist);
return cleanup(p);
}
if (change_uid(pw->pw_uid, &p->old_uid)) {
pam_syslog(pamh, LOG_ERR,
"pam_modutil_drop_priv: change_uid failed: %m");
(void) change_gid(p->old_gid, NULL);
(void) setgroups(p->number_of_groups, p->grplist);
return cleanup(p);
}
p->is_dropped = PRIV_MAGIC;
return 0;
}
int pam_modutil_regain_priv(pam_handle_t *pamh,
struct pam_modutil_privs *p)
{
switch (p->is_dropped) {
case PRIV_MAGIC_DONOTHING:
p->is_dropped = 0;
return 0;
case PRIV_MAGIC:
break;
default:
pam_syslog(pamh, LOG_CRIT,
"pam_modutil_regain_priv: called with invalid state");
return -1;
}
if (change_uid(p->old_uid, NULL)) {
pam_syslog(pamh, LOG_ERR,
"pam_modutil_regain_priv: change_uid failed: %m");
return cleanup(p);
}
if (change_gid(p->old_gid, NULL)) {
pam_syslog(pamh, LOG_ERR,
"pam_modutil_regain_priv: change_gid failed: %m");
return cleanup(p);
}
if (setgroups(p->number_of_groups, p->grplist)) {
pam_syslog(pamh, LOG_ERR,
"pam_modutil_regain_priv: setgroups failed: %m");
return cleanup(p);
}
p->is_dropped = 0;
cleanup(p);
return 0;
}
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