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 /// UNNEEDED by elogind
39 int have_effective_cap(int value) {
40 _cleanup_cap_free_ cap_t cap;
47 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;
57 _cleanup_free_ char *content = NULL;
64 /* available since linux-3.2 */
65 r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
67 r = safe_atolu(content, &p);
75 /* fall back to syscall-probing for pre linux-3.2 */
76 p = (unsigned long) CAP_LAST_CAP;
78 if (prctl(PR_CAPBSET_READ, p) < 0) {
80 /* Hmm, look downwards, until we find one that
82 for (p--; p > 0; p --)
83 if (prctl(PR_CAPBSET_READ, p) >= 0)
88 /* Hmm, look upwards, until we find one that doesn't
91 if (prctl(PR_CAPBSET_READ, p+1) < 0)
101 /// UNNEEDED by elogind
103 int capability_bounding_set_drop(uint64_t drop, bool right_now) {
104 _cleanup_cap_free_ cap_t after_cap = NULL;
109 /* If we are run as PID 1 we will lack CAP_SETPCAP by default
110 * in the effective set (yes, the kernel drops that when
111 * executing init!), so get it back temporarily so that we can
112 * call PR_CAPBSET_DROP. */
114 after_cap = cap_get_proc();
118 if (cap_get_flag(after_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
122 _cleanup_cap_free_ cap_t temp_cap = NULL;
123 static const cap_value_t v = CAP_SETPCAP;
125 temp_cap = cap_dup(after_cap);
131 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) {
136 if (cap_set_proc(temp_cap) < 0) {
142 for (i = 0; i <= cap_last_cap(); i++) {
144 if (drop & ((uint64_t) 1ULL << (uint64_t) i)) {
147 /* Drop it from the bounding set */
148 if (prctl(PR_CAPBSET_DROP, i) < 0) {
154 /* Also drop it from the inheritable set, so
155 * that anything we exec() loses the
156 * capability for good. */
157 if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
162 /* If we shall apply this right now drop it
163 * also from our own capability sets. */
165 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
166 cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
177 if (cap_set_proc(after_cap) < 0)
183 static int drop_from_file(const char *fn, uint64_t drop) {
186 uint64_t current, after;
189 r = read_one_line_file(fn, &p);
193 assert_cc(sizeof(hi) == sizeof(unsigned));
194 assert_cc(sizeof(lo) == sizeof(unsigned));
196 k = sscanf(p, "%u %u", &lo, &hi);
202 current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
203 after = current & ~drop;
205 if (current == after)
208 lo = (unsigned) (after & 0xFFFFFFFFULL);
209 hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
211 if (asprintf(&p, "%u %u", lo, hi) < 0)
214 r = write_string_file(fn, p, WRITE_STRING_FILE_CREATE);
220 int capability_bounding_set_drop_usermode(uint64_t drop) {
223 r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop);
227 r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop);
234 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
235 _cleanup_cap_free_ cap_t d = NULL;
239 /* Unfortunately we cannot leave privilege dropping to PID 1
240 * here, since we want to run as user but want to keep some
241 * capabilities. Since file capabilities have been introduced
242 * this cannot be done across exec() anymore, unless our
243 * binary has the capability configured in the file system,
244 * which we want to avoid. */
246 if (setresgid(gid, gid, gid) < 0)
247 return log_error_errno(errno, "Failed to change group ID: %m");
249 if (setgroups(0, NULL) < 0)
250 return log_error_errno(errno, "Failed to drop auxiliary groups list: %m");
252 /* Ensure we keep the permitted caps across the setresuid() */
253 if (prctl(PR_SET_KEEPCAPS, 1) < 0)
254 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
256 r = setresuid(uid, uid, uid);
258 return log_error_errno(errno, "Failed to change user ID: %m");
260 if (prctl(PR_SET_KEEPCAPS, 0) < 0)
261 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
263 /* Drop all caps from the bounding set, except the ones we want */
264 r = capability_bounding_set_drop(~keep_capabilities, true);
266 return log_error_errno(r, "Failed to drop capabilities: %m");
268 /* Now upgrade the permitted caps we still kept to effective caps */
273 if (keep_capabilities) {
274 cap_value_t bits[u64log2(keep_capabilities) + 1];
276 for (i = 0; i < ELEMENTSOF(bits); i++)
277 if (keep_capabilities & (1ULL << i))
280 /* use enough bits */
281 assert(i == 64 || (keep_capabilities >> i) == 0);
282 /* don't use too many bits */
283 assert(keep_capabilities & (1ULL << (i - 1)));
285 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
286 cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0)
287 return log_error_errno(errno, "Failed to enable capabilities bits: %m");
289 if (cap_set_proc(d) < 0)
290 return log_error_errno(errno, "Failed to increase capabilities: %m");
296 int drop_capability(cap_value_t cv) {
297 _cleanup_cap_free_ cap_t tmp_cap = NULL;
299 tmp_cap = cap_get_proc();
303 if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
304 (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
305 (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
308 if (cap_set_proc(tmp_cap) < 0)