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/*
SSSD
Kerberos 5 Backend Module -- Utilities
Authors:
Sumit Bose <sbose@redhat.com>
Copyright (C) 2009 Red Hat
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "util/util.h"
#include <grp.h>
errno_t become_user(uid_t uid, gid_t gid)
{
uid_t cuid;
int ret;
DEBUG(SSSDBG_FUNC_DATA,
"Trying to become user [%"SPRIuid"][%"SPRIgid"].\n", uid, gid);
/* skip call if we already are the requested user */
cuid = geteuid();
if (uid == cuid) {
DEBUG(SSSDBG_FUNC_DATA, "Already user [%"SPRIuid"].\n", uid);
return EOK;
}
/* drop supplmentary groups first */
ret = setgroups(0, NULL);
if (ret == -1) {
ret = errno;
DEBUG(SSSDBG_CRIT_FAILURE,
"setgroups failed [%d][%s].\n", ret, strerror(ret));
return ret;
}
/* change gid so that root cannot be regained (changes saved gid too) */
ret = setresgid(gid, gid, gid);
if (ret == -1) {
ret = errno;
DEBUG(SSSDBG_CRIT_FAILURE,
"setresgid failed [%d][%s].\n", ret, strerror(ret));
return ret;
}
/* change uid so that root cannot be regained (changes saved uid too) */
/* this call also takes care of dropping CAP_SETUID, so this is a PNR */
ret = setresuid(uid, uid, uid);
if (ret == -1) {
ret = errno;
DEBUG(SSSDBG_CRIT_FAILURE,
"setresuid failed [%d][%s].\n", ret, strerror(ret));
return ret;
}
return EOK;
}
struct sss_creds {
uid_t uid;
gid_t gid;
int num_gids;
gid_t gids[];
};
errno_t restore_creds(struct sss_creds *saved_creds);
/* This is a reversible version of become_user, and returns the saved
* credentials so that creds can be switched back calling restore_creds */
errno_t switch_creds(TALLOC_CTX *mem_ctx,
uid_t uid, gid_t gid,
int num_gids, gid_t *gids,
struct sss_creds **saved_creds)
{
struct sss_creds *ssc = NULL;
int size;
int ret;
DEBUG(SSSDBG_FUNC_DATA, "Switch user to [%d][%d].\n", uid, gid);
if (saved_creds) {
/* save current user credentials */
size = getgroups(0, NULL);
if (size == -1) {
ret = errno;
DEBUG(SSSDBG_CRIT_FAILURE, "Getgroups failed! (%d, %s)\n",
ret, strerror(ret));
goto done;
}
ssc = talloc_size(mem_ctx,
(sizeof(struct sss_creds) + size * sizeof(gid_t)));
if (!ssc) {
DEBUG(SSSDBG_CRIT_FAILURE, "Allocation failed!\n");
ret = ENOMEM;
goto done;
}
ssc->num_gids = size;
size = getgroups(ssc->num_gids, ssc->gids);
if (size == -1) {
ret = errno;
DEBUG(SSSDBG_CRIT_FAILURE, "Getgroups failed! (%d, %s)\n",
ret, strerror(ret));
/* free ssc immediately otherwise the code will try to restore
* wrong creds */
talloc_zfree(ssc);
goto done;
}
/* we care only about effective ids */
ssc->uid = geteuid();
ssc->gid = getegid();
}
/* if we are regaining root set euid first so that we have CAP_SETUID back,
* ane the other calls work too, otherwise call it last so that we can
* change groups before we loose CAP_SETUID */
if (uid == 0) {
ret = setresuid(0, 0, 0);
if (ret == -1) {
ret = errno;
DEBUG(SSSDBG_CRIT_FAILURE,
"setresuid failed [%d][%s].\n", ret, strerror(ret));
goto done;
}
}
/* TODO: use prctl to get/set capabilities too ? */
/* try to setgroups first should always work if CAP_SETUID is set,
* otherwise it will always fail, failure is not critical though as
* generally we only really care about uid and at mot primary gid */
ret = setgroups(num_gids, gids);
if (ret == -1) {
ret = errno;
DEBUG(SSSDBG_TRACE_FUNC,
"setgroups failed [%d][%s].\n", ret, strerror(ret));
}
/* change gid now, (leaves saved gid to current, so we can restore) */
ret = setresgid(-1, gid, -1);
if (ret == -1) {
ret = errno;
DEBUG(SSSDBG_CRIT_FAILURE,
"setresgid failed [%d][%s].\n", ret, strerror(ret));
goto done;
}
if (uid != 0) {
/* change uid, (leaves saved uid to current, so we can restore) */
ret = setresuid(-1, uid, -1);
if (ret == -1) {
ret = errno;
DEBUG(SSSDBG_CRIT_FAILURE,
"setresuid failed [%d][%s].\n", ret, strerror(ret));
goto done;
}
}
ret = 0;
done:
if (ret) {
if (ssc) {
/* attempt to restore creds first */
restore_creds(ssc);
talloc_free(ssc);
}
} else if (saved_creds) {
*saved_creds = ssc;
}
return ret;
}
errno_t restore_creds(struct sss_creds *saved_creds)
{
return switch_creds(saved_creds,
saved_creds->uid,
saved_creds->gid,
saved_creds->num_gids,
saved_creds->gids, NULL);
}
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