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>
33 #include "capability.h"
35 int have_effective_cap(int value) {
36 _cleanup_cap_free_ cap_t cap;
43 if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
49 unsigned long cap_last_cap(void) {
50 static thread_local unsigned long saved;
51 static thread_local bool valid = false;
52 _cleanup_free_ char *content = NULL;
59 /* available since linux-3.2 */
60 r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
62 r = safe_atolu(content, &p);
70 /* fall back to syscall-probing for pre linux-3.2 */
71 p = (unsigned long) CAP_LAST_CAP;
73 if (prctl(PR_CAPBSET_READ, p) < 0) {
75 /* Hmm, look downwards, until we find one that
77 for (p--; p > 0; p --)
78 if (prctl(PR_CAPBSET_READ, p) >= 0)
83 /* Hmm, look upwards, until we find one that doesn't
86 if (prctl(PR_CAPBSET_READ, p+1) < 0)
96 int capability_bounding_set_drop(uint64_t drop, bool right_now) {
97 _cleanup_cap_free_ cap_t after_cap = NULL;
102 /* If we are run as PID 1 we will lack CAP_SETPCAP by default
103 * in the effective set (yes, the kernel drops that when
104 * executing init!), so get it back temporarily so that we can
105 * call PR_CAPBSET_DROP. */
107 after_cap = cap_get_proc();
111 if (cap_get_flag(after_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
115 _cleanup_cap_free_ cap_t temp_cap = NULL;
116 static const cap_value_t v = CAP_SETPCAP;
118 temp_cap = cap_dup(after_cap);
124 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) {
129 if (cap_set_proc(temp_cap) < 0) {
135 for (i = 0; i <= cap_last_cap(); i++) {
137 if (drop & ((uint64_t) 1ULL << (uint64_t) i)) {
140 /* Drop it from the bounding set */
141 if (prctl(PR_CAPBSET_DROP, i) < 0) {
147 /* Also drop it from the inheritable set, so
148 * that anything we exec() loses the
149 * capability for good. */
150 if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
155 /* If we shall apply this right now drop it
156 * also from our own capability sets. */
158 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
159 cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
170 if (cap_set_proc(after_cap) < 0)
176 static int drop_from_file(const char *fn, uint64_t drop) {
179 uint64_t current, after;
182 r = read_one_line_file(fn, &p);
186 assert_cc(sizeof(hi) == sizeof(unsigned));
187 assert_cc(sizeof(lo) == sizeof(unsigned));
189 k = sscanf(p, "%u %u", &lo, &hi);
195 current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
196 after = current & ~drop;
198 if (current == after)
201 lo = (unsigned) (after & 0xFFFFFFFFULL);
202 hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
204 if (asprintf(&p, "%u %u", lo, hi) < 0)
207 r = write_string_file(fn, p, WRITE_STRING_FILE_CREATE);
213 int capability_bounding_set_drop_usermode(uint64_t drop) {
216 r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop);
220 r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop);
227 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
228 _cleanup_cap_free_ cap_t d = NULL;
232 /* Unfortunately we cannot leave privilege dropping to PID 1
233 * here, since we want to run as user but want to keep some
234 * capabilities. Since file capabilities have been introduced
235 * this cannot be done across exec() anymore, unless our
236 * binary has the capability configured in the file system,
237 * which we want to avoid. */
239 if (setresgid(gid, gid, gid) < 0)
240 return log_error_errno(errno, "Failed to change group ID: %m");
242 if (setgroups(0, NULL) < 0)
243 return log_error_errno(errno, "Failed to drop auxiliary groups list: %m");
245 /* Ensure we keep the permitted caps across the setresuid() */
246 if (prctl(PR_SET_KEEPCAPS, 1) < 0)
247 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
249 r = setresuid(uid, uid, uid);
251 return log_error_errno(errno, "Failed to change user ID: %m");
253 if (prctl(PR_SET_KEEPCAPS, 0) < 0)
254 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
256 /* Drop all caps from the bounding set, except the ones we want */
257 r = capability_bounding_set_drop(~keep_capabilities, true);
259 return log_error_errno(r, "Failed to drop capabilities: %m");
261 /* Now upgrade the permitted caps we still kept to effective caps */
266 if (keep_capabilities) {
267 cap_value_t bits[u64log2(keep_capabilities) + 1];
269 for (i = 0; i < ELEMENTSOF(bits); i++)
270 if (keep_capabilities & (1ULL << i))
273 /* use enough bits */
274 assert(i == 64 || (keep_capabilities >> i) == 0);
275 /* don't use too many bits */
276 assert(keep_capabilities & (1ULL << (i - 1)));
278 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
279 cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) {
280 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)