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Commit | Line | Data |
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53e1b683 | 1 | /* SPDX-License-Identifier: LGPL-2.1+ */ |
d7832d2c | 2 | |
d7832d2c | 3 | #include <errno.h> |
3ffd4af2 | 4 | #include <grp.h> |
d7832d2c | 5 | #include <stdio.h> |
11c3a366 | 6 | #include <stdlib.h> |
d7832d2c KS |
7 | #include <sys/capability.h> |
8 | #include <sys/prctl.h> | |
3ffd4af2 | 9 | #include <unistd.h> |
d7832d2c | 10 | |
b5efdb8a | 11 | #include "alloc-util.h" |
430f0182 | 12 | #include "capability-util.h" |
3ffd4af2 LP |
13 | #include "fileio.h" |
14 | #include "log.h" | |
d7832d2c | 15 | #include "macro.h" |
6bedfcbb | 16 | #include "parse-util.h" |
36d85478 | 17 | #include "user-util.h" |
d7832d2c | 18 | #include "util.h" |
d7832d2c KS |
19 | |
20 | int have_effective_cap(int value) { | |
5ce70e5b | 21 | _cleanup_cap_free_ cap_t cap; |
d7832d2c | 22 | cap_flag_value_t fv; |
d7832d2c | 23 | |
ec8927ca LP |
24 | cap = cap_get_proc(); |
25 | if (!cap) | |
d7832d2c KS |
26 | return -errno; |
27 | ||
28 | if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0) | |
5ce70e5b | 29 | return -errno; |
d7832d2c | 30 | else |
5ce70e5b | 31 | return fv == CAP_SET; |
d7832d2c KS |
32 | } |
33 | ||
34 | unsigned long cap_last_cap(void) { | |
ec202eae SL |
35 | static thread_local unsigned long saved; |
36 | static thread_local bool valid = false; | |
80b43783 | 37 | _cleanup_free_ char *content = NULL; |
a7f7d1bd | 38 | unsigned long p = 0; |
80b43783 | 39 | int r; |
d7832d2c KS |
40 | |
41 | if (valid) | |
42 | return saved; | |
43 | ||
80b43783 DH |
44 | /* available since linux-3.2 */ |
45 | r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content); | |
46 | if (r >= 0) { | |
47 | r = safe_atolu(content, &p); | |
48 | if (r >= 0) { | |
49 | saved = p; | |
50 | valid = true; | |
51 | return p; | |
52 | } | |
53 | } | |
54 | ||
55 | /* fall back to syscall-probing for pre linux-3.2 */ | |
d7832d2c KS |
56 | p = (unsigned long) CAP_LAST_CAP; |
57 | ||
58 | if (prctl(PR_CAPBSET_READ, p) < 0) { | |
59 | ||
60 | /* Hmm, look downwards, until we find one that | |
61 | * works */ | |
62 | for (p--; p > 0; p --) | |
63 | if (prctl(PR_CAPBSET_READ, p) >= 0) | |
64 | break; | |
65 | ||
66 | } else { | |
67 | ||
68 | /* Hmm, look upwards, until we find one that doesn't | |
69 | * work */ | |
70 | for (;; p++) | |
71 | if (prctl(PR_CAPBSET_READ, p+1) < 0) | |
72 | break; | |
73 | } | |
74 | ||
75 | saved = p; | |
76 | valid = true; | |
77 | ||
78 | return p; | |
79 | } | |
ec8927ca | 80 | |
755d4b67 IP |
81 | int capability_update_inherited_set(cap_t caps, uint64_t set) { |
82 | unsigned long i; | |
83 | ||
84 | /* Add capabilities in the set to the inherited caps. Do not apply | |
85 | * them yet. */ | |
86 | ||
87 | for (i = 0; i < cap_last_cap(); i++) { | |
88 | ||
89 | if (set & (UINT64_C(1) << i)) { | |
90 | cap_value_t v; | |
91 | ||
92 | v = (cap_value_t) i; | |
93 | ||
94 | /* Make the capability inheritable. */ | |
95 | if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, CAP_SET) < 0) | |
96 | return -errno; | |
97 | } | |
98 | } | |
99 | ||
100 | return 0; | |
101 | } | |
102 | ||
103 | int capability_ambient_set_apply(uint64_t set, bool also_inherit) { | |
104 | unsigned long i; | |
105 | _cleanup_cap_free_ cap_t caps = NULL; | |
106 | ||
107 | /* Add the capabilities to the ambient set. */ | |
108 | ||
109 | if (also_inherit) { | |
110 | int r; | |
111 | caps = cap_get_proc(); | |
112 | if (!caps) | |
113 | return -errno; | |
114 | ||
115 | r = capability_update_inherited_set(caps, set); | |
116 | if (r < 0) | |
117 | return -errno; | |
118 | ||
119 | if (cap_set_proc(caps) < 0) | |
120 | return -errno; | |
121 | } | |
122 | ||
123 | for (i = 0; i < cap_last_cap(); i++) { | |
124 | ||
125 | if (set & (UINT64_C(1) << i)) { | |
126 | ||
127 | /* Add the capability to the ambient set. */ | |
128 | if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0) | |
129 | return -errno; | |
130 | } | |
131 | } | |
132 | ||
133 | return 0; | |
134 | } | |
135 | ||
a103496c | 136 | int capability_bounding_set_drop(uint64_t keep, bool right_now) { |
6067611a | 137 | _cleanup_cap_free_ cap_t before_cap = NULL, after_cap = NULL; |
ec8927ca | 138 | cap_flag_value_t fv; |
6a010ac9 | 139 | unsigned long i; |
ec8927ca LP |
140 | int r; |
141 | ||
142 | /* If we are run as PID 1 we will lack CAP_SETPCAP by default | |
143 | * in the effective set (yes, the kernel drops that when | |
144 | * executing init!), so get it back temporarily so that we can | |
145 | * call PR_CAPBSET_DROP. */ | |
146 | ||
6067611a LP |
147 | before_cap = cap_get_proc(); |
148 | if (!before_cap) | |
ec8927ca LP |
149 | return -errno; |
150 | ||
6067611a | 151 | if (cap_get_flag(before_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0) |
ec8927ca | 152 | return -errno; |
ec8927ca LP |
153 | |
154 | if (fv != CAP_SET) { | |
6a010ac9 | 155 | _cleanup_cap_free_ cap_t temp_cap = NULL; |
ec8927ca LP |
156 | static const cap_value_t v = CAP_SETPCAP; |
157 | ||
6067611a LP |
158 | temp_cap = cap_dup(before_cap); |
159 | if (!temp_cap) | |
160 | return -errno; | |
ec8927ca | 161 | |
6067611a LP |
162 | if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) |
163 | return -errno; | |
ec8927ca | 164 | |
6067611a LP |
165 | if (cap_set_proc(temp_cap) < 0) |
166 | log_debug_errno(errno, "Can't acquire effective CAP_SETPCAP bit, ignoring: %m"); | |
167 | ||
168 | /* If we didn't manage to acquire the CAP_SETPCAP bit, we continue anyway, after all this just means | |
169 | * we'll fail later, when we actually intend to drop some capabilities. */ | |
ec8927ca LP |
170 | } |
171 | ||
6067611a LP |
172 | after_cap = cap_dup(before_cap); |
173 | if (!after_cap) | |
174 | return -errno; | |
175 | ||
ec8927ca | 176 | for (i = 0; i <= cap_last_cap(); i++) { |
6067611a | 177 | cap_value_t v; |
ec8927ca | 178 | |
6067611a LP |
179 | if ((keep & (UINT64_C(1) << i))) |
180 | continue; | |
ec8927ca | 181 | |
6067611a LP |
182 | /* Drop it from the bounding set */ |
183 | if (prctl(PR_CAPBSET_DROP, i) < 0) { | |
184 | r = -errno; | |
185 | ||
186 | /* If dropping the capability failed, let's see if we didn't have it in the first place. If so, | |
187 | * continue anyway, as dropping a capability we didn't have in the first place doesn't really | |
188 | * matter anyway. */ | |
189 | if (prctl(PR_CAPBSET_READ, i) != 0) | |
ec8927ca | 190 | goto finish; |
6067611a LP |
191 | } |
192 | v = (cap_value_t) i; | |
193 | ||
194 | /* Also drop it from the inheritable set, so | |
195 | * that anything we exec() loses the | |
196 | * capability for good. */ | |
197 | if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) { | |
198 | r = -errno; | |
199 | goto finish; | |
200 | } | |
ec8927ca | 201 | |
6067611a LP |
202 | /* If we shall apply this right now drop it |
203 | * also from our own capability sets. */ | |
204 | if (right_now) { | |
205 | if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 || | |
206 | cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) { | |
ec8927ca LP |
207 | r = -errno; |
208 | goto finish; | |
209 | } | |
ec8927ca LP |
210 | } |
211 | } | |
212 | ||
213 | r = 0; | |
214 | ||
215 | finish: | |
6067611a LP |
216 | if (cap_set_proc(after_cap) < 0) { |
217 | /* If there are no actual changes anyway then let's ignore this error. */ | |
218 | if (cap_compare(before_cap, after_cap) != 0) | |
219 | r = -errno; | |
220 | } | |
ec8927ca LP |
221 | |
222 | return r; | |
223 | } | |
939b8f14 | 224 | |
a103496c | 225 | static int drop_from_file(const char *fn, uint64_t keep) { |
3130fca5 | 226 | _cleanup_free_ char *p = NULL; |
939b8f14 | 227 | uint64_t current, after; |
3130fca5 LP |
228 | uint32_t hi, lo; |
229 | int r, k; | |
939b8f14 LP |
230 | |
231 | r = read_one_line_file(fn, &p); | |
232 | if (r < 0) | |
233 | return r; | |
234 | ||
235 | assert_cc(sizeof(hi) == sizeof(unsigned)); | |
236 | assert_cc(sizeof(lo) == sizeof(unsigned)); | |
237 | ||
238 | k = sscanf(p, "%u %u", &lo, &hi); | |
939b8f14 LP |
239 | if (k != 2) |
240 | return -EIO; | |
241 | ||
242 | current = (uint64_t) lo | ((uint64_t) hi << 32ULL); | |
a103496c | 243 | after = current & keep; |
939b8f14 LP |
244 | |
245 | if (current == after) | |
246 | return 0; | |
247 | ||
248 | lo = (unsigned) (after & 0xFFFFFFFFULL); | |
249 | hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL); | |
250 | ||
3130fca5 | 251 | return write_string_filef(fn, WRITE_STRING_FILE_CREATE, "%u %u", lo, hi); |
939b8f14 LP |
252 | } |
253 | ||
a103496c | 254 | int capability_bounding_set_drop_usermode(uint64_t keep) { |
939b8f14 LP |
255 | int r; |
256 | ||
a103496c | 257 | r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep); |
939b8f14 LP |
258 | if (r < 0) |
259 | return r; | |
260 | ||
a103496c | 261 | r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep); |
939b8f14 LP |
262 | if (r < 0) |
263 | return r; | |
264 | ||
265 | return r; | |
266 | } | |
966bff26 | 267 | |
ed617ec2 | 268 | int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) { |
966bff26 | 269 | _cleanup_cap_free_ cap_t d = NULL; |
f11943c5 | 270 | unsigned i, j = 0; |
966bff26 LP |
271 | int r; |
272 | ||
273 | /* Unfortunately we cannot leave privilege dropping to PID 1 | |
274 | * here, since we want to run as user but want to keep some | |
275 | * capabilities. Since file capabilities have been introduced | |
276 | * this cannot be done across exec() anymore, unless our | |
277 | * binary has the capability configured in the file system, | |
278 | * which we want to avoid. */ | |
279 | ||
4a62c710 MS |
280 | if (setresgid(gid, gid, gid) < 0) |
281 | return log_error_errno(errno, "Failed to change group ID: %m"); | |
966bff26 | 282 | |
97f0e76f LP |
283 | r = maybe_setgroups(0, NULL); |
284 | if (r < 0) | |
285 | return log_error_errno(r, "Failed to drop auxiliary groups list: %m"); | |
966bff26 | 286 | |
51ddf615 ZJS |
287 | /* Ensure we keep the permitted caps across the setresuid() */ |
288 | if (prctl(PR_SET_KEEPCAPS, 1) < 0) | |
4a62c710 | 289 | return log_error_errno(errno, "Failed to enable keep capabilities flag: %m"); |
966bff26 | 290 | |
b1c05b98 | 291 | if (setresuid(uid, uid, uid) < 0) |
4a62c710 | 292 | return log_error_errno(errno, "Failed to change user ID: %m"); |
966bff26 | 293 | |
4a62c710 MS |
294 | if (prctl(PR_SET_KEEPCAPS, 0) < 0) |
295 | return log_error_errno(errno, "Failed to disable keep capabilities flag: %m"); | |
966bff26 | 296 | |
f11943c5 | 297 | /* Drop all caps from the bounding set, except the ones we want */ |
a103496c | 298 | r = capability_bounding_set_drop(keep_capabilities, true); |
f647962d MS |
299 | if (r < 0) |
300 | return log_error_errno(r, "Failed to drop capabilities: %m"); | |
966bff26 | 301 | |
f11943c5 | 302 | /* Now upgrade the permitted caps we still kept to effective caps */ |
966bff26 LP |
303 | d = cap_init(); |
304 | if (!d) | |
305 | return log_oom(); | |
306 | ||
51ddf615 | 307 | if (keep_capabilities) { |
057255fb | 308 | cap_value_t bits[u64log2(keep_capabilities) + 1]; |
6a010ac9 | 309 | |
7d328b54 | 310 | for (i = 0; i < ELEMENTSOF(bits); i++) |
51ddf615 ZJS |
311 | if (keep_capabilities & (1ULL << i)) |
312 | bits[j++] = i; | |
057255fb | 313 | |
2c9fc266 ZJS |
314 | /* use enough bits */ |
315 | assert(i == 64 || (keep_capabilities >> i) == 0); | |
316 | /* don't use too many bits */ | |
317 | assert(keep_capabilities & (1ULL << (i - 1))); | |
966bff26 | 318 | |
51ddf615 | 319 | if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 || |
e1427b13 MS |
320 | cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) |
321 | return log_error_errno(errno, "Failed to enable capabilities bits: %m"); | |
51ddf615 ZJS |
322 | |
323 | if (cap_set_proc(d) < 0) | |
324 | return log_error_errno(errno, "Failed to increase capabilities: %m"); | |
325 | } | |
966bff26 LP |
326 | |
327 | return 0; | |
328 | } | |
dd5ae4c3 PK |
329 | |
330 | int drop_capability(cap_value_t cv) { | |
331 | _cleanup_cap_free_ cap_t tmp_cap = NULL; | |
332 | ||
333 | tmp_cap = cap_get_proc(); | |
334 | if (!tmp_cap) | |
335 | return -errno; | |
336 | ||
337 | if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) || | |
338 | (cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) || | |
339 | (cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0)) | |
340 | return -errno; | |
341 | ||
342 | if (cap_set_proc(tmp_cap) < 0) | |
343 | return -errno; | |
344 | ||
345 | return 0; | |
346 | } | |
39f608e4 LP |
347 | |
348 | bool ambient_capabilities_supported(void) { | |
349 | static int cache = -1; | |
350 | ||
351 | if (cache >= 0) | |
352 | return cache; | |
353 | ||
354 | /* If PR_CAP_AMBIENT returns something valid, or an unexpected error code we assume that ambient caps are | |
355 | * available. */ | |
356 | ||
357 | cache = prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_KILL, 0, 0) >= 0 || | |
358 | !IN_SET(errno, EINVAL, EOPNOTSUPP, ENOSYS); | |
359 | ||
360 | return cache; | |
361 | } |