1 /* SPDX-License-Identifier: LGPL-2.1+ */
3 Copyright 2010 Lennart Poettering
10 #include <sys/capability.h>
11 #include <sys/prctl.h>
14 #include "alloc-util.h"
15 #include "capability-util.h"
19 #include "parse-util.h"
20 #include "user-util.h"
23 #if 0 /// UNNEEDED by elogind
24 int have_effective_cap(int value) {
25 _cleanup_cap_free_ cap_t cap;
32 if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
39 unsigned long cap_last_cap(void) {
40 static thread_local unsigned long saved;
41 static thread_local bool valid = false;
42 _cleanup_free_ char *content = NULL;
49 /* available since linux-3.2 */
50 r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
52 r = safe_atolu(content, &p);
60 /* fall back to syscall-probing for pre linux-3.2 */
61 p = (unsigned long) CAP_LAST_CAP;
63 if (prctl(PR_CAPBSET_READ, p) < 0) {
65 /* Hmm, look downwards, until we find one that
67 for (p--; p > 0; p --)
68 if (prctl(PR_CAPBSET_READ, p) >= 0)
73 /* Hmm, look upwards, until we find one that doesn't
76 if (prctl(PR_CAPBSET_READ, p+1) < 0)
86 #if 0 /// UNNEEDED by elogind
87 int capability_update_inherited_set(cap_t caps, uint64_t set) {
90 /* Add capabilities in the set to the inherited caps. Do not apply
93 for (i = 0; i < cap_last_cap(); i++) {
95 if (set & (UINT64_C(1) << i)) {
100 /* Make the capability inheritable. */
101 if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, CAP_SET) < 0)
109 int capability_ambient_set_apply(uint64_t set, bool also_inherit) {
111 _cleanup_cap_free_ cap_t caps = NULL;
113 /* Add the capabilities to the ambient set. */
117 caps = cap_get_proc();
121 r = capability_update_inherited_set(caps, set);
125 if (cap_set_proc(caps) < 0)
129 for (i = 0; i < cap_last_cap(); i++) {
131 if (set & (UINT64_C(1) << i)) {
133 /* Add the capability to the ambient set. */
134 if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0)
142 int capability_bounding_set_drop(uint64_t keep, bool right_now) {
143 _cleanup_cap_free_ cap_t before_cap = NULL, after_cap = NULL;
148 /* If we are run as PID 1 we will lack CAP_SETPCAP by default
149 * in the effective set (yes, the kernel drops that when
150 * executing init!), so get it back temporarily so that we can
151 * call PR_CAPBSET_DROP. */
153 before_cap = cap_get_proc();
157 if (cap_get_flag(before_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
161 _cleanup_cap_free_ cap_t temp_cap = NULL;
162 static const cap_value_t v = CAP_SETPCAP;
164 temp_cap = cap_dup(before_cap);
168 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0)
171 if (cap_set_proc(temp_cap) < 0)
172 log_debug_errno(errno, "Can't acquire effective CAP_SETPCAP bit, ignoring: %m");
174 /* If we didn't manage to acquire the CAP_SETPCAP bit, we continue anyway, after all this just means
175 * we'll fail later, when we actually intend to drop some capabilities. */
178 after_cap = cap_dup(before_cap);
182 for (i = 0; i <= cap_last_cap(); i++) {
185 if ((keep & (UINT64_C(1) << i)))
188 /* Drop it from the bounding set */
189 if (prctl(PR_CAPBSET_DROP, i) < 0) {
192 /* If dropping the capability failed, let's see if we didn't have it in the first place. If so,
193 * continue anyway, as dropping a capability we didn't have in the first place doesn't really
195 if (prctl(PR_CAPBSET_READ, i) != 0)
200 /* Also drop it from the inheritable set, so
201 * that anything we exec() loses the
202 * capability for good. */
203 if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
208 /* If we shall apply this right now drop it
209 * also from our own capability sets. */
211 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
212 cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
222 if (cap_set_proc(after_cap) < 0) {
223 /* If there are no actual changes anyway then let's ignore this error. */
224 if (cap_compare(before_cap, after_cap) != 0)
231 static int drop_from_file(const char *fn, uint64_t keep) {
232 _cleanup_free_ char *p = NULL;
233 uint64_t current, after;
237 r = read_one_line_file(fn, &p);
241 assert_cc(sizeof(hi) == sizeof(unsigned));
242 assert_cc(sizeof(lo) == sizeof(unsigned));
244 k = sscanf(p, "%u %u", &lo, &hi);
248 current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
249 after = current & keep;
251 if (current == after)
254 lo = (unsigned) (after & 0xFFFFFFFFULL);
255 hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
257 return write_string_filef(fn, WRITE_STRING_FILE_CREATE, "%u %u", lo, hi);
260 int capability_bounding_set_drop_usermode(uint64_t keep) {
263 r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep);
267 r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep);
274 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
275 _cleanup_cap_free_ cap_t d = NULL;
279 /* Unfortunately we cannot leave privilege dropping to PID 1
280 * here, since we want to run as user but want to keep some
281 * capabilities. Since file capabilities have been introduced
282 * this cannot be done across exec() anymore, unless our
283 * binary has the capability configured in the file system,
284 * which we want to avoid. */
286 if (setresgid(gid, gid, gid) < 0)
287 return log_error_errno(errno, "Failed to change group ID: %m");
289 r = maybe_setgroups(0, NULL);
291 return log_error_errno(r, "Failed to drop auxiliary groups list: %m");
293 /* Ensure we keep the permitted caps across the setresuid() */
294 if (prctl(PR_SET_KEEPCAPS, 1) < 0)
295 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
297 if (setresuid(uid, uid, uid) < 0)
298 return log_error_errno(errno, "Failed to change user ID: %m");
300 if (prctl(PR_SET_KEEPCAPS, 0) < 0)
301 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
303 /* Drop all caps from the bounding set, except the ones we want */
304 r = capability_bounding_set_drop(keep_capabilities, true);
306 return log_error_errno(r, "Failed to drop capabilities: %m");
308 /* Now upgrade the permitted caps we still kept to effective caps */
313 if (keep_capabilities) {
314 cap_value_t bits[u64log2(keep_capabilities) + 1];
316 for (i = 0; i < ELEMENTSOF(bits); i++)
317 if (keep_capabilities & (1ULL << i))
320 /* use enough bits */
321 assert(i == 64 || (keep_capabilities >> i) == 0);
322 /* don't use too many bits */
323 assert(keep_capabilities & (1ULL << (i - 1)));
325 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
326 cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0)
327 return log_error_errno(errno, "Failed to enable capabilities bits: %m");
329 if (cap_set_proc(d) < 0)
330 return log_error_errno(errno, "Failed to increase capabilities: %m");
336 int drop_capability(cap_value_t cv) {
337 _cleanup_cap_free_ cap_t tmp_cap = NULL;
339 tmp_cap = cap_get_proc();
343 if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
344 (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
345 (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
348 if (cap_set_proc(tmp_cap) < 0)
354 bool ambient_capabilities_supported(void) {
355 static int cache = -1;
360 /* If PR_CAP_AMBIENT returns something valid, or an unexpected error code we assume that ambient caps are
363 cache = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_KILL, 0, 0) >= 0 ||
364 !IN_SET(errno, EINVAL, EOPNOTSUPP, ENOSYS);