2 This file is part of systemd.
4 Copyright 2010 Lennart Poettering
6 systemd is free software; you can redistribute it and/or modify it
7 under the terms of the GNU Lesser General Public License as published by
8 the Free Software Foundation; either version 2.1 of the License, or
9 (at your option) any later version.
11 systemd is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public License
17 along with systemd; If not, see <http://www.gnu.org/licenses/>.
24 #include <sys/capability.h>
25 #include <sys/prctl.h>
28 #include "alloc-util.h"
29 #include "capability-util.h"
33 #include "parse-util.h"
36 #if 0 /// UNNEEDED by elogind
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)
52 unsigned long cap_last_cap(void) {
53 static thread_local unsigned long saved;
54 static thread_local bool valid = false;
55 _cleanup_free_ char *content = NULL;
62 /* available since linux-3.2 */
63 r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
65 r = safe_atolu(content, &p);
73 /* fall back to syscall-probing for pre linux-3.2 */
74 p = (unsigned long) CAP_LAST_CAP;
76 if (prctl(PR_CAPBSET_READ, p) < 0) {
78 /* Hmm, look downwards, until we find one that
80 for (p--; p > 0; p --)
81 if (prctl(PR_CAPBSET_READ, p) >= 0)
86 /* Hmm, look upwards, until we find one that doesn't
89 if (prctl(PR_CAPBSET_READ, p+1) < 0)
99 #if 0 /// UNNEEDED by elogind
100 int capability_update_inherited_set(cap_t caps, uint64_t set) {
103 /* Add capabilities in the set to the inherited caps. Do not apply
106 for (i = 0; i < cap_last_cap(); i++) {
108 if (set & (UINT64_C(1) << i)) {
113 /* Make the capability inheritable. */
114 if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, CAP_SET) < 0)
122 int capability_ambient_set_apply(uint64_t set, bool also_inherit) {
124 _cleanup_cap_free_ cap_t caps = NULL;
126 /* Add the capabilities to the ambient set. */
130 caps = cap_get_proc();
134 r = capability_update_inherited_set(caps, set);
138 if (cap_set_proc(caps) < 0)
142 for (i = 0; i < cap_last_cap(); i++) {
144 if (set & (UINT64_C(1) << i)) {
146 /* Add the capability to the ambient set. */
147 if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0)
155 int capability_bounding_set_drop(uint64_t keep, bool right_now) {
156 _cleanup_cap_free_ cap_t after_cap = NULL;
161 /* If we are run as PID 1 we will lack CAP_SETPCAP by default
162 * in the effective set (yes, the kernel drops that when
163 * executing init!), so get it back temporarily so that we can
164 * call PR_CAPBSET_DROP. */
166 after_cap = cap_get_proc();
170 if (cap_get_flag(after_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
174 _cleanup_cap_free_ cap_t temp_cap = NULL;
175 static const cap_value_t v = CAP_SETPCAP;
177 temp_cap = cap_dup(after_cap);
183 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) {
188 if (cap_set_proc(temp_cap) < 0) {
194 for (i = 0; i <= cap_last_cap(); i++) {
196 if (!(keep & (UINT64_C(1) << i))) {
199 /* Drop it from the bounding set */
200 if (prctl(PR_CAPBSET_DROP, i) < 0) {
206 /* Also drop it from the inheritable set, so
207 * that anything we exec() loses the
208 * capability for good. */
209 if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
214 /* If we shall apply this right now drop it
215 * also from our own capability sets. */
217 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
218 cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
229 if (cap_set_proc(after_cap) < 0)
235 static int drop_from_file(const char *fn, uint64_t keep) {
238 uint64_t current, after;
241 r = read_one_line_file(fn, &p);
245 assert_cc(sizeof(hi) == sizeof(unsigned));
246 assert_cc(sizeof(lo) == sizeof(unsigned));
248 k = sscanf(p, "%u %u", &lo, &hi);
254 current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
255 after = current & keep;
257 if (current == after)
260 lo = (unsigned) (after & 0xFFFFFFFFULL);
261 hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
263 if (asprintf(&p, "%u %u", lo, hi) < 0)
266 r = write_string_file(fn, p, WRITE_STRING_FILE_CREATE);
272 int capability_bounding_set_drop_usermode(uint64_t keep) {
275 r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep);
279 r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep);
286 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
287 _cleanup_cap_free_ cap_t d = NULL;
291 /* Unfortunately we cannot leave privilege dropping to PID 1
292 * here, since we want to run as user but want to keep some
293 * capabilities. Since file capabilities have been introduced
294 * this cannot be done across exec() anymore, unless our
295 * binary has the capability configured in the file system,
296 * which we want to avoid. */
298 if (setresgid(gid, gid, gid) < 0)
299 return log_error_errno(errno, "Failed to change group ID: %m");
301 if (setgroups(0, NULL) < 0)
302 return log_error_errno(errno, "Failed to drop auxiliary groups list: %m");
304 /* Ensure we keep the permitted caps across the setresuid() */
305 if (prctl(PR_SET_KEEPCAPS, 1) < 0)
306 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
308 r = setresuid(uid, uid, uid);
310 return log_error_errno(errno, "Failed to change user ID: %m");
312 if (prctl(PR_SET_KEEPCAPS, 0) < 0)
313 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
315 /* Drop all caps from the bounding set, except the ones we want */
316 r = capability_bounding_set_drop(keep_capabilities, true);
318 return log_error_errno(r, "Failed to drop capabilities: %m");
320 /* Now upgrade the permitted caps we still kept to effective caps */
325 if (keep_capabilities) {
326 cap_value_t bits[u64log2(keep_capabilities) + 1];
328 for (i = 0; i < ELEMENTSOF(bits); i++)
329 if (keep_capabilities & (1ULL << i))
332 /* use enough bits */
333 assert(i == 64 || (keep_capabilities >> i) == 0);
334 /* don't use too many bits */
335 assert(keep_capabilities & (1ULL << (i - 1)));
337 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
338 cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0)
339 return log_error_errno(errno, "Failed to enable capabilities bits: %m");
341 if (cap_set_proc(d) < 0)
342 return log_error_errno(errno, "Failed to increase capabilities: %m");
348 int drop_capability(cap_value_t cv) {
349 _cleanup_cap_free_ cap_t tmp_cap = NULL;
351 tmp_cap = cap_get_proc();
355 if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
356 (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
357 (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
360 if (cap_set_proc(tmp_cap) < 0)