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) {
88 _cleanup_cap_free_ cap_t after_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 _cleanup_cap_free_ cap_t temp_cap = NULL;
107 static const cap_value_t v = CAP_SETPCAP;
109 temp_cap = cap_dup(after_cap);
115 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) {
120 if (cap_set_proc(temp_cap) < 0) {
126 for (i = 0; i <= cap_last_cap(); i++) {
128 if (drop & ((uint64_t) 1ULL << (uint64_t) i)) {
131 /* Drop it from the bounding set */
132 if (prctl(PR_CAPBSET_DROP, i) < 0) {
138 /* Also drop it from the inheritable set, so
139 * that anything we exec() loses the
140 * capability for good. */
141 if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
146 /* If we shall apply this right now drop it
147 * also from our own capability sets. */
149 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
150 cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
161 if (cap_set_proc(after_cap) < 0)
167 static int drop_from_file(const char *fn, uint64_t drop) {
170 uint64_t current, after;
173 r = read_one_line_file(fn, &p);
177 assert_cc(sizeof(hi) == sizeof(unsigned));
178 assert_cc(sizeof(lo) == sizeof(unsigned));
180 k = sscanf(p, "%u %u", &lo, &hi);
186 current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
187 after = current & ~drop;
189 if (current == after)
192 lo = (unsigned) (after & 0xFFFFFFFFULL);
193 hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
195 if (asprintf(&p, "%u %u", lo, hi) < 0)
198 r = write_string_file(fn, p);
204 int capability_bounding_set_drop_usermode(uint64_t drop) {
207 r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop);
211 r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop);
218 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
220 _cleanup_cap_free_ cap_t d = NULL;
223 /* Unfortunately we cannot leave privilege dropping to PID 1
224 * here, since we want to run as user but want to keep some
225 * capabilities. Since file capabilities have been introduced
226 * this cannot be done across exec() anymore, unless our
227 * binary has the capability configured in the file system,
228 * which we want to avoid. */
230 if (setresgid(gid, gid, gid) < 0)
231 return log_error_errno(errno, "Failed to change group ID: %m");
233 if (setgroups(0, NULL) < 0)
234 return log_error_errno(errno, "Failed to drop auxiliary groups list: %m");
236 if (prctl(PR_SET_KEEPCAPS, 1) < 0)
237 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
239 r = setresuid(uid, uid, uid);
241 return log_error_errno(errno, "Failed to change user ID: %m");
243 if (prctl(PR_SET_KEEPCAPS, 0) < 0)
244 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
246 r = capability_bounding_set_drop(~keep_capabilities, true);
248 return log_error_errno(r, "Failed to drop capabilities: %m");
254 if (keep_capabilities) {
255 cap_value_t bits[sizeof(keep_capabilities)*8];
258 for (i = 0; i < sizeof(keep_capabilities)*8; i++)
259 if (keep_capabilities & (1ULL << i))
262 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
263 cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) {
264 log_error_errno(errno, "Failed to enable capabilities bits: %m");
269 if (cap_set_proc(d) < 0)
270 return log_error_errno(errno, "Failed to increase capabilities: %m");