1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
|
/*
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;
uid_t myuid;
uid_t mygid;
DEBUG(SSSDBG_FUNC_DATA, "Switch user to [%d][%d].\n", uid, gid);
myuid = geteuid();
mygid = getegid();
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 = myuid;
ssc->gid = mygid;
}
/* 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 libcap-ng if we need to get/set capabilities too ? */
if (myuid == uid && mygid == gid) {
DEBUG(SSSDBG_FUNC_DATA, "Already user [%"SPRIuid"].\n", uid);
return EOK;
}
/* 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) {
/* 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)
{
if (saved_creds == NULL) {
/* In case save_creds was saved with the UID already dropped */
return EOK;
}
return switch_creds(saved_creds,
saved_creds->uid,
saved_creds->gid,
saved_creds->num_gids,
saved_creds->gids, NULL);
}
|
