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"
34 #include "user-util.h"
37 #if 0 /// UNNEEDED by elogind
38 int have_effective_cap(int value) {
39 _cleanup_cap_free_ cap_t cap;
46 if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
53 unsigned long cap_last_cap(void) {
54 static thread_local unsigned long saved;
55 static thread_local bool valid = false;
56 _cleanup_free_ char *content = NULL;
63 /* available since linux-3.2 */
64 r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
66 r = safe_atolu(content, &p);
74 /* fall back to syscall-probing for pre linux-3.2 */
75 p = (unsigned long) CAP_LAST_CAP;
77 if (prctl(PR_CAPBSET_READ, p) < 0) {
79 /* Hmm, look downwards, until we find one that
81 for (p--; p > 0; p --)
82 if (prctl(PR_CAPBSET_READ, p) >= 0)
87 /* Hmm, look upwards, until we find one that doesn't
90 if (prctl(PR_CAPBSET_READ, p+1) < 0)
100 #if 0 /// UNNEEDED by elogind
101 int capability_update_inherited_set(cap_t caps, uint64_t set) {
104 /* Add capabilities in the set to the inherited caps. Do not apply
107 for (i = 0; i < cap_last_cap(); i++) {
109 if (set & (UINT64_C(1) << i)) {
114 /* Make the capability inheritable. */
115 if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, CAP_SET) < 0)
123 int capability_ambient_set_apply(uint64_t set, bool also_inherit) {
125 _cleanup_cap_free_ cap_t caps = NULL;
127 /* Add the capabilities to the ambient set. */
131 caps = cap_get_proc();
135 r = capability_update_inherited_set(caps, set);
139 if (cap_set_proc(caps) < 0)
143 for (i = 0; i < cap_last_cap(); i++) {
145 if (set & (UINT64_C(1) << i)) {
147 /* Add the capability to the ambient set. */
148 if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0)
156 int capability_bounding_set_drop(uint64_t keep, bool right_now) {
157 _cleanup_cap_free_ cap_t before_cap = NULL, after_cap = NULL;
162 /* If we are run as PID 1 we will lack CAP_SETPCAP by default
163 * in the effective set (yes, the kernel drops that when
164 * executing init!), so get it back temporarily so that we can
165 * call PR_CAPBSET_DROP. */
167 before_cap = cap_get_proc();
171 if (cap_get_flag(before_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
175 _cleanup_cap_free_ cap_t temp_cap = NULL;
176 static const cap_value_t v = CAP_SETPCAP;
178 temp_cap = cap_dup(before_cap);
182 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0)
185 if (cap_set_proc(temp_cap) < 0)
186 log_debug_errno(errno, "Can't acquire effective CAP_SETPCAP bit, ignoring: %m");
188 /* If we didn't manage to acquire the CAP_SETPCAP bit, we continue anyway, after all this just means
189 * we'll fail later, when we actually intend to drop some capabilities. */
192 after_cap = cap_dup(before_cap);
196 for (i = 0; i <= cap_last_cap(); i++) {
199 if ((keep & (UINT64_C(1) << i)))
202 /* Drop it from the bounding set */
203 if (prctl(PR_CAPBSET_DROP, i) < 0) {
206 /* If dropping the capability failed, let's see if we didn't have it in the first place. If so,
207 * continue anyway, as dropping a capability we didn't have in the first place doesn't really
209 if (prctl(PR_CAPBSET_READ, i) != 0)
214 /* Also drop it from the inheritable set, so
215 * that anything we exec() loses the
216 * capability for good. */
217 if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
222 /* If we shall apply this right now drop it
223 * also from our own capability sets. */
225 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
226 cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
236 if (cap_set_proc(after_cap) < 0) {
237 /* If there are no actual changes anyway then let's ignore this error. */
238 if (cap_compare(before_cap, after_cap) != 0)
245 static int drop_from_file(const char *fn, uint64_t keep) {
248 uint64_t current, after;
251 r = read_one_line_file(fn, &p);
255 assert_cc(sizeof(hi) == sizeof(unsigned));
256 assert_cc(sizeof(lo) == sizeof(unsigned));
258 k = sscanf(p, "%u %u", &lo, &hi);
264 current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
265 after = current & keep;
267 if (current == after)
270 lo = (unsigned) (after & 0xFFFFFFFFULL);
271 hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
273 if (asprintf(&p, "%u %u", lo, hi) < 0)
276 r = write_string_file(fn, p, WRITE_STRING_FILE_CREATE);
282 int capability_bounding_set_drop_usermode(uint64_t keep) {
285 r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep);
289 r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep);
296 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
297 _cleanup_cap_free_ cap_t d = NULL;
301 /* Unfortunately we cannot leave privilege dropping to PID 1
302 * here, since we want to run as user but want to keep some
303 * capabilities. Since file capabilities have been introduced
304 * this cannot be done across exec() anymore, unless our
305 * binary has the capability configured in the file system,
306 * which we want to avoid. */
308 if (setresgid(gid, gid, gid) < 0)
309 return log_error_errno(errno, "Failed to change group ID: %m");
311 r = maybe_setgroups(0, NULL);
313 return log_error_errno(r, "Failed to drop auxiliary groups list: %m");
315 /* Ensure we keep the permitted caps across the setresuid() */
316 if (prctl(PR_SET_KEEPCAPS, 1) < 0)
317 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
319 r = setresuid(uid, uid, uid);
321 return log_error_errno(errno, "Failed to change user ID: %m");
323 if (prctl(PR_SET_KEEPCAPS, 0) < 0)
324 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
326 /* Drop all caps from the bounding set, except the ones we want */
327 r = capability_bounding_set_drop(keep_capabilities, true);
329 return log_error_errno(r, "Failed to drop capabilities: %m");
331 /* Now upgrade the permitted caps we still kept to effective caps */
336 if (keep_capabilities) {
337 cap_value_t bits[u64log2(keep_capabilities) + 1];
339 for (i = 0; i < ELEMENTSOF(bits); i++)
340 if (keep_capabilities & (1ULL << i))
343 /* use enough bits */
344 assert(i == 64 || (keep_capabilities >> i) == 0);
345 /* don't use too many bits */
346 assert(keep_capabilities & (1ULL << (i - 1)));
348 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
349 cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0)
350 return log_error_errno(errno, "Failed to enable capabilities bits: %m");
352 if (cap_set_proc(d) < 0)
353 return log_error_errno(errno, "Failed to increase capabilities: %m");
359 int drop_capability(cap_value_t cv) {
360 _cleanup_cap_free_ cap_t tmp_cap = NULL;
362 tmp_cap = cap_get_proc();
366 if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
367 (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
368 (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
371 if (cap_set_proc(tmp_cap) < 0)
377 bool ambient_capabilities_supported(void) {
378 static int cache = -1;
383 /* If PR_CAP_AMBIENT returns something valid, or an unexpected error code we assume that ambient caps are
386 cache = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_KILL, 0, 0) >= 0 ||
387 !IN_SET(errno, EINVAL, EOPNOTSUPP, ENOSYS);