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/>.
27 #include <sys/types.h>
30 #include <sys/capability.h>
31 #include <sys/prctl.h>
38 #include "capability.h"
40 int have_effective_cap(int value) {
41 _cleanup_cap_free_ cap_t cap;
48 if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
54 unsigned long cap_last_cap(void) {
55 static thread_local unsigned long saved;
56 static thread_local bool valid = false;
62 p = (unsigned long) CAP_LAST_CAP;
64 if (prctl(PR_CAPBSET_READ, p) < 0) {
66 /* Hmm, look downwards, until we find one that
68 for (p--; p > 0; p --)
69 if (prctl(PR_CAPBSET_READ, p) >= 0)
74 /* Hmm, look upwards, until we find one that doesn't
77 if (prctl(PR_CAPBSET_READ, p+1) < 0)
87 int capability_bounding_set_drop(uint64_t drop, bool right_now) {
89 _cleanup_cap_free_ cap_t after_cap = NULL, temp_cap = NULL;
93 /* If we are run as PID 1 we will lack CAP_SETPCAP by default
94 * in the effective set (yes, the kernel drops that when
95 * executing init!), so get it back temporarily so that we can
96 * call PR_CAPBSET_DROP. */
98 after_cap = cap_get_proc();
102 if (cap_get_flag(after_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
106 static const cap_value_t v = CAP_SETPCAP;
108 temp_cap = cap_dup(after_cap);
114 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) {
119 if (cap_set_proc(temp_cap) < 0) {
125 for (i = 0; i <= cap_last_cap(); i++) {
127 if (drop & ((uint64_t) 1ULL << (uint64_t) i)) {
130 /* Drop it from the bounding set */
131 if (prctl(PR_CAPBSET_DROP, i) < 0) {
137 /* Also drop it from the inheritable set, so
138 * that anything we exec() loses the
139 * capability for good. */
140 if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
145 /* If we shall apply this right now drop it
146 * also from our own capability sets. */
148 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
149 cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
160 if (cap_set_proc(after_cap) < 0)
166 static int drop_from_file(const char *fn, uint64_t drop) {
169 uint64_t current, after;
172 r = read_one_line_file(fn, &p);
176 assert_cc(sizeof(hi) == sizeof(unsigned));
177 assert_cc(sizeof(lo) == sizeof(unsigned));
179 k = sscanf(p, "%u %u", &lo, &hi);
185 current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
186 after = current & ~drop;
188 if (current == after)
191 lo = (unsigned) (after & 0xFFFFFFFFULL);
192 hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
194 if (asprintf(&p, "%u %u", lo, hi) < 0)
197 r = write_string_file(fn, p);
203 int capability_bounding_set_drop_usermode(uint64_t drop) {
206 r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop);
210 r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop);
217 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
219 _cleanup_cap_free_ cap_t d = NULL;
220 cap_value_t bits[sizeof(keep_capabilities)*8];
224 /* Unfortunately we cannot leave privilege dropping to PID 1
225 * here, since we want to run as user but want to keep some
226 * capabilities. Since file capabilities have been introduced
227 * this cannot be done across exec() anymore, unless our
228 * binary has the capability configured in the file system,
229 * which we want to avoid. */
231 if (setresgid(gid, gid, gid) < 0) {
232 log_error("Failed change group ID: %m");
236 if (setgroups(0, NULL) < 0) {
237 log_error("Failed to drop auxiliary groups list: %m");
241 if (prctl(PR_SET_KEEPCAPS, 1) < 0) {
242 log_error("Failed to enable keep capabilities flag: %m");
246 r = setresuid(uid, uid, uid);
248 log_error("Failed change user ID: %m");
252 if (prctl(PR_SET_KEEPCAPS, 0) < 0) {
253 log_error("Failed to disable keep capabilities flag: %m");
257 r = capability_bounding_set_drop(~keep_capabilities, true);
259 log_error("Failed to drop capabilities: %s", strerror(-r));
267 for (i = 0; i < sizeof(keep_capabilities)*8; i++)
268 if (keep_capabilities & (1ULL << i))
271 if (keep_capabilities) {
272 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
273 cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) {
274 log_error("Failed to enable capabilities bits: %m");
279 if (cap_set_proc(d) < 0) {
280 log_error("Failed to increase capabilities: %m");