1 /* SPDX-License-Identifier: LGPL-2.1+ */
7 #include <sys/capability.h>
11 #include "alloc-util.h"
12 #include "capability-util.h"
16 #include "parse-util.h"
17 #include "user-util.h"
20 #if 0 /// UNNEEDED by elogind
21 int have_effective_cap(int value) {
22 _cleanup_cap_free_ cap_t cap;
29 if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
36 unsigned long cap_last_cap(void) {
37 static thread_local unsigned long saved;
38 static thread_local bool valid = false;
39 _cleanup_free_ char *content = NULL;
46 /* available since linux-3.2 */
47 r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
49 r = safe_atolu(content, &p);
57 /* fall back to syscall-probing for pre linux-3.2 */
58 p = (unsigned long) CAP_LAST_CAP;
60 if (prctl(PR_CAPBSET_READ, p) < 0) {
62 /* Hmm, look downwards, until we find one that
64 for (p--; p > 0; p --)
65 if (prctl(PR_CAPBSET_READ, p) >= 0)
70 /* Hmm, look upwards, until we find one that doesn't
73 if (prctl(PR_CAPBSET_READ, p+1) < 0)
83 #if 0 /// UNNEEDED by elogind
84 int capability_update_inherited_set(cap_t caps, uint64_t set) {
87 /* Add capabilities in the set to the inherited caps. Do not apply
90 for (i = 0; i < cap_last_cap(); i++) {
92 if (set & (UINT64_C(1) << i)) {
97 /* Make the capability inheritable. */
98 if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, CAP_SET) < 0)
106 int capability_ambient_set_apply(uint64_t set, bool also_inherit) {
108 _cleanup_cap_free_ cap_t caps = NULL;
110 /* Add the capabilities to the ambient set. */
114 caps = cap_get_proc();
118 r = capability_update_inherited_set(caps, set);
122 if (cap_set_proc(caps) < 0)
126 for (i = 0; i < cap_last_cap(); i++) {
128 if (set & (UINT64_C(1) << i)) {
130 /* Add the capability to the ambient set. */
131 if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0)
139 int capability_bounding_set_drop(uint64_t keep, bool right_now) {
140 _cleanup_cap_free_ cap_t before_cap = NULL, after_cap = NULL;
145 /* If we are run as PID 1 we will lack CAP_SETPCAP by default
146 * in the effective set (yes, the kernel drops that when
147 * executing init!), so get it back temporarily so that we can
148 * call PR_CAPBSET_DROP. */
150 before_cap = cap_get_proc();
154 if (cap_get_flag(before_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
158 _cleanup_cap_free_ cap_t temp_cap = NULL;
159 static const cap_value_t v = CAP_SETPCAP;
161 temp_cap = cap_dup(before_cap);
165 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0)
168 if (cap_set_proc(temp_cap) < 0)
169 log_debug_errno(errno, "Can't acquire effective CAP_SETPCAP bit, ignoring: %m");
171 /* If we didn't manage to acquire the CAP_SETPCAP bit, we continue anyway, after all this just means
172 * we'll fail later, when we actually intend to drop some capabilities. */
175 after_cap = cap_dup(before_cap);
179 for (i = 0; i <= cap_last_cap(); i++) {
182 if ((keep & (UINT64_C(1) << i)))
185 /* Drop it from the bounding set */
186 if (prctl(PR_CAPBSET_DROP, i) < 0) {
189 /* If dropping the capability failed, let's see if we didn't have it in the first place. If so,
190 * continue anyway, as dropping a capability we didn't have in the first place doesn't really
192 if (prctl(PR_CAPBSET_READ, i) != 0)
197 /* Also drop it from the inheritable set, so
198 * that anything we exec() loses the
199 * capability for good. */
200 if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
205 /* If we shall apply this right now drop it
206 * also from our own capability sets. */
208 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
209 cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
219 if (cap_set_proc(after_cap) < 0) {
220 /* If there are no actual changes anyway then let's ignore this error. */
221 if (cap_compare(before_cap, after_cap) != 0)
228 static int drop_from_file(const char *fn, uint64_t keep) {
229 _cleanup_free_ char *p = NULL;
230 uint64_t current, after;
234 r = read_one_line_file(fn, &p);
238 assert_cc(sizeof(hi) == sizeof(unsigned));
239 assert_cc(sizeof(lo) == sizeof(unsigned));
241 k = sscanf(p, "%u %u", &lo, &hi);
245 current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
246 after = current & keep;
248 if (current == after)
251 lo = (unsigned) (after & 0xFFFFFFFFULL);
252 hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
254 return write_string_filef(fn, WRITE_STRING_FILE_CREATE, "%u %u", lo, hi);
257 int capability_bounding_set_drop_usermode(uint64_t keep) {
260 r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep);
264 r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep);
271 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
272 _cleanup_cap_free_ cap_t d = NULL;
276 /* Unfortunately we cannot leave privilege dropping to PID 1
277 * here, since we want to run as user but want to keep some
278 * capabilities. Since file capabilities have been introduced
279 * this cannot be done across exec() anymore, unless our
280 * binary has the capability configured in the file system,
281 * which we want to avoid. */
283 if (setresgid(gid, gid, gid) < 0)
284 return log_error_errno(errno, "Failed to change group ID: %m");
286 r = maybe_setgroups(0, NULL);
288 return log_error_errno(r, "Failed to drop auxiliary groups list: %m");
290 /* Ensure we keep the permitted caps across the setresuid() */
291 if (prctl(PR_SET_KEEPCAPS, 1) < 0)
292 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
294 if (setresuid(uid, uid, uid) < 0)
295 return log_error_errno(errno, "Failed to change user ID: %m");
297 if (prctl(PR_SET_KEEPCAPS, 0) < 0)
298 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
300 /* Drop all caps from the bounding set, except the ones we want */
301 r = capability_bounding_set_drop(keep_capabilities, true);
303 return log_error_errno(r, "Failed to drop capabilities: %m");
305 /* Now upgrade the permitted caps we still kept to effective caps */
310 if (keep_capabilities) {
311 cap_value_t bits[u64log2(keep_capabilities) + 1];
313 for (i = 0; i < ELEMENTSOF(bits); i++)
314 if (keep_capabilities & (1ULL << i))
317 /* use enough bits */
318 assert(i == 64 || (keep_capabilities >> i) == 0);
319 /* don't use too many bits */
320 assert(keep_capabilities & (1ULL << (i - 1)));
322 if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
323 cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0)
324 return log_error_errno(errno, "Failed to enable capabilities bits: %m");
326 if (cap_set_proc(d) < 0)
327 return log_error_errno(errno, "Failed to increase capabilities: %m");
333 int drop_capability(cap_value_t cv) {
334 _cleanup_cap_free_ cap_t tmp_cap = NULL;
336 tmp_cap = cap_get_proc();
340 if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
341 (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
342 (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
345 if (cap_set_proc(tmp_cap) < 0)
351 bool ambient_capabilities_supported(void) {
352 static int cache = -1;
357 /* If PR_CAP_AMBIENT returns something valid, or an unexpected error code we assume that ambient caps are
360 cache = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_KILL, 0, 0) >= 0 ||
361 !IN_SET(errno, EINVAL, EOPNOTSUPP, ENOSYS);