1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
4 This file is part of systemd.
6 Copyright 2010 Lennart Poettering
8 systemd is free software; you can redistribute it and/or modify it
9 under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 2.1 of the License, or
11 (at your option) any later version.
13 systemd is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 Lesser General Public License for more details.
18 You should have received a copy of the GNU Lesser General Public License
19 along with systemd; If not, see <http://www.gnu.org/licenses/>.
25 #include <sys/capability.h>
26 #include <sys/prctl.h>
29 #include "alloc-util.h"
30 #include "capability-util.h"
34 #include "parse-util.h"
37 int have_effective_cap(int value
) {
38 _cleanup_cap_free_ cap_t cap
;
45 if (cap_get_flag(cap
, value
, CAP_EFFECTIVE
, &fv
) < 0)
51 unsigned long cap_last_cap(void) {
52 static thread_local
unsigned long saved
;
53 static thread_local
bool valid
= false;
54 _cleanup_free_
char *content
= NULL
;
61 /* available since linux-3.2 */
62 r
= read_one_line_file("/proc/sys/kernel/cap_last_cap", &content
);
64 r
= safe_atolu(content
, &p
);
72 /* fall back to syscall-probing for pre linux-3.2 */
73 p
= (unsigned long) CAP_LAST_CAP
;
75 if (prctl(PR_CAPBSET_READ
, p
) < 0) {
77 /* Hmm, look downwards, until we find one that
79 for (p
--; p
> 0; p
--)
80 if (prctl(PR_CAPBSET_READ
, p
) >= 0)
85 /* Hmm, look upwards, until we find one that doesn't
88 if (prctl(PR_CAPBSET_READ
, p
+1) < 0)
98 int capability_bounding_set_drop(uint64_t drop
, bool right_now
) {
99 _cleanup_cap_free_ cap_t after_cap
= NULL
;
104 /* If we are run as PID 1 we will lack CAP_SETPCAP by default
105 * in the effective set (yes, the kernel drops that when
106 * executing init!), so get it back temporarily so that we can
107 * call PR_CAPBSET_DROP. */
109 after_cap
= cap_get_proc();
113 if (cap_get_flag(after_cap
, CAP_SETPCAP
, CAP_EFFECTIVE
, &fv
) < 0)
117 _cleanup_cap_free_ cap_t temp_cap
= NULL
;
118 static const cap_value_t v
= CAP_SETPCAP
;
120 temp_cap
= cap_dup(after_cap
);
126 if (cap_set_flag(temp_cap
, CAP_EFFECTIVE
, 1, &v
, CAP_SET
) < 0) {
131 if (cap_set_proc(temp_cap
) < 0) {
137 for (i
= 0; i
<= cap_last_cap(); i
++) {
139 if (drop
& ((uint64_t) 1ULL << (uint64_t) i
)) {
142 /* Drop it from the bounding set */
143 if (prctl(PR_CAPBSET_DROP
, i
) < 0) {
149 /* Also drop it from the inheritable set, so
150 * that anything we exec() loses the
151 * capability for good. */
152 if (cap_set_flag(after_cap
, CAP_INHERITABLE
, 1, &v
, CAP_CLEAR
) < 0) {
157 /* If we shall apply this right now drop it
158 * also from our own capability sets. */
160 if (cap_set_flag(after_cap
, CAP_PERMITTED
, 1, &v
, CAP_CLEAR
) < 0 ||
161 cap_set_flag(after_cap
, CAP_EFFECTIVE
, 1, &v
, CAP_CLEAR
) < 0) {
172 if (cap_set_proc(after_cap
) < 0)
178 static int drop_from_file(const char *fn
, uint64_t drop
) {
181 uint64_t current
, after
;
184 r
= read_one_line_file(fn
, &p
);
188 assert_cc(sizeof(hi
) == sizeof(unsigned));
189 assert_cc(sizeof(lo
) == sizeof(unsigned));
191 k
= sscanf(p
, "%u %u", &lo
, &hi
);
197 current
= (uint64_t) lo
| ((uint64_t) hi
<< 32ULL);
198 after
= current
& ~drop
;
200 if (current
== after
)
203 lo
= (unsigned) (after
& 0xFFFFFFFFULL
);
204 hi
= (unsigned) ((after
>> 32ULL) & 0xFFFFFFFFULL
);
206 if (asprintf(&p
, "%u %u", lo
, hi
) < 0)
209 r
= write_string_file(fn
, p
, WRITE_STRING_FILE_CREATE
);
215 int capability_bounding_set_drop_usermode(uint64_t drop
) {
218 r
= drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop
);
222 r
= drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop
);
229 int drop_privileges(uid_t uid
, gid_t gid
, uint64_t keep_capabilities
) {
230 _cleanup_cap_free_ cap_t d
= NULL
;
234 /* Unfortunately we cannot leave privilege dropping to PID 1
235 * here, since we want to run as user but want to keep some
236 * capabilities. Since file capabilities have been introduced
237 * this cannot be done across exec() anymore, unless our
238 * binary has the capability configured in the file system,
239 * which we want to avoid. */
241 if (setresgid(gid
, gid
, gid
) < 0)
242 return log_error_errno(errno
, "Failed to change group ID: %m");
244 if (setgroups(0, NULL
) < 0)
245 return log_error_errno(errno
, "Failed to drop auxiliary groups list: %m");
247 /* Ensure we keep the permitted caps across the setresuid() */
248 if (prctl(PR_SET_KEEPCAPS
, 1) < 0)
249 return log_error_errno(errno
, "Failed to enable keep capabilities flag: %m");
251 r
= setresuid(uid
, uid
, uid
);
253 return log_error_errno(errno
, "Failed to change user ID: %m");
255 if (prctl(PR_SET_KEEPCAPS
, 0) < 0)
256 return log_error_errno(errno
, "Failed to disable keep capabilities flag: %m");
258 /* Drop all caps from the bounding set, except the ones we want */
259 r
= capability_bounding_set_drop(~keep_capabilities
, true);
261 return log_error_errno(r
, "Failed to drop capabilities: %m");
263 /* Now upgrade the permitted caps we still kept to effective caps */
268 if (keep_capabilities
) {
269 cap_value_t bits
[u64log2(keep_capabilities
) + 1];
271 for (i
= 0; i
< ELEMENTSOF(bits
); i
++)
272 if (keep_capabilities
& (1ULL << i
))
275 /* use enough bits */
276 assert(i
== 64 || (keep_capabilities
>> i
) == 0);
277 /* don't use too many bits */
278 assert(keep_capabilities
& (1ULL << (i
- 1)));
280 if (cap_set_flag(d
, CAP_EFFECTIVE
, j
, bits
, CAP_SET
) < 0 ||
281 cap_set_flag(d
, CAP_PERMITTED
, j
, bits
, CAP_SET
) < 0)
282 return log_error_errno(errno
, "Failed to enable capabilities bits: %m");
284 if (cap_set_proc(d
) < 0)
285 return log_error_errno(errno
, "Failed to increase capabilities: %m");
291 int drop_capability(cap_value_t cv
) {
292 _cleanup_cap_free_ cap_t tmp_cap
= NULL
;
294 tmp_cap
= cap_get_proc();
298 if ((cap_set_flag(tmp_cap
, CAP_INHERITABLE
, 1, &cv
, CAP_CLEAR
) < 0) ||
299 (cap_set_flag(tmp_cap
, CAP_PERMITTED
, 1, &cv
, CAP_CLEAR
) < 0) ||
300 (cap_set_flag(tmp_cap
, CAP_EFFECTIVE
, 1, &cv
, CAP_CLEAR
) < 0))
303 if (cap_set_proc(tmp_cap
) < 0)