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1 | /* The tunable framework. See the README.tunables to know how to use the | |
2 | tunable in a glibc module. | |
3 | ||
4 | Copyright (C) 2016-2019 Free Software Foundation, Inc. | |
5 | This file is part of the GNU C Library. | |
6 | ||
7 | The GNU C Library is free software; you can redistribute it and/or | |
8 | modify it under the terms of the GNU Lesser General Public | |
9 | License as published by the Free Software Foundation; either | |
10 | version 2.1 of the License, or (at your option) any later version. | |
11 | ||
12 | The GNU C Library is distributed in the hope that it will be useful, | |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | Lesser General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU Lesser General Public | |
18 | License along with the GNU C Library; if not, see | |
19 | <http://www.gnu.org/licenses/>. */ | |
20 | ||
21 | #include <startup.h> | |
22 | #include <stdint.h> | |
23 | #include <stdbool.h> | |
24 | #include <unistd.h> | |
25 | #include <stdlib.h> | |
26 | #include <sysdep.h> | |
27 | #include <fcntl.h> | |
28 | #include <ldsodefs.h> | |
29 | ||
30 | #define TUNABLES_INTERNAL 1 | |
31 | #include "dl-tunables.h" | |
32 | ||
33 | #include <not-errno.h> | |
34 | ||
35 | #if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring | |
36 | # define GLIBC_TUNABLES "GLIBC_TUNABLES" | |
37 | #endif | |
38 | ||
39 | #if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring | |
40 | static char * | |
41 | tunables_strdup (const char *in) | |
42 | { | |
43 | size_t i = 0; | |
44 | ||
45 | while (in[i++] != '\0'); | |
46 | char *out = __sbrk (i); | |
47 | ||
48 | /* FIXME: In reality if the allocation fails, __sbrk will crash attempting to | |
49 | set the thread-local errno since the TCB has not yet been set up. This | |
50 | needs to be fixed with an __sbrk implementation that does not set | |
51 | errno. */ | |
52 | if (out == (void *)-1) | |
53 | return NULL; | |
54 | ||
55 | i--; | |
56 | ||
57 | while (i-- > 0) | |
58 | out[i] = in[i]; | |
59 | ||
60 | return out; | |
61 | } | |
62 | #endif | |
63 | ||
64 | static char ** | |
65 | get_next_env (char **envp, char **name, size_t *namelen, char **val, | |
66 | char ***prev_envp) | |
67 | { | |
68 | while (envp != NULL && *envp != NULL) | |
69 | { | |
70 | char **prev = envp; | |
71 | char *envline = *envp++; | |
72 | int len = 0; | |
73 | ||
74 | while (envline[len] != '\0' && envline[len] != '=') | |
75 | len++; | |
76 | ||
77 | /* Just the name and no value, go to the next one. */ | |
78 | if (envline[len] == '\0') | |
79 | continue; | |
80 | ||
81 | *name = envline; | |
82 | *namelen = len; | |
83 | *val = &envline[len + 1]; | |
84 | *prev_envp = prev; | |
85 | ||
86 | return envp; | |
87 | } | |
88 | ||
89 | return NULL; | |
90 | } | |
91 | ||
92 | #define TUNABLE_SET_VAL_IF_VALID_RANGE(__cur, __val, __type) \ | |
93 | ({ \ | |
94 | __type min = (__cur)->type.min; \ | |
95 | __type max = (__cur)->type.max; \ | |
96 | \ | |
97 | if ((__type) (__val) >= min && (__type) (val) <= max) \ | |
98 | { \ | |
99 | (__cur)->val.numval = val; \ | |
100 | (__cur)->initialized = true; \ | |
101 | } \ | |
102 | }) | |
103 | ||
104 | static void | |
105 | do_tunable_update_val (tunable_t *cur, const void *valp) | |
106 | { | |
107 | uint64_t val; | |
108 | ||
109 | if (cur->type.type_code != TUNABLE_TYPE_STRING) | |
110 | val = *((int64_t *) valp); | |
111 | ||
112 | switch (cur->type.type_code) | |
113 | { | |
114 | case TUNABLE_TYPE_INT_32: | |
115 | { | |
116 | TUNABLE_SET_VAL_IF_VALID_RANGE (cur, val, int64_t); | |
117 | break; | |
118 | } | |
119 | case TUNABLE_TYPE_UINT_64: | |
120 | { | |
121 | TUNABLE_SET_VAL_IF_VALID_RANGE (cur, val, uint64_t); | |
122 | break; | |
123 | } | |
124 | case TUNABLE_TYPE_SIZE_T: | |
125 | { | |
126 | TUNABLE_SET_VAL_IF_VALID_RANGE (cur, val, uint64_t); | |
127 | break; | |
128 | } | |
129 | case TUNABLE_TYPE_STRING: | |
130 | { | |
131 | cur->val.strval = valp; | |
132 | break; | |
133 | } | |
134 | default: | |
135 | __builtin_unreachable (); | |
136 | } | |
137 | } | |
138 | ||
139 | /* Validate range of the input value and initialize the tunable CUR if it looks | |
140 | good. */ | |
141 | static void | |
142 | tunable_initialize (tunable_t *cur, const char *strval) | |
143 | { | |
144 | uint64_t val; | |
145 | const void *valp; | |
146 | ||
147 | if (cur->type.type_code != TUNABLE_TYPE_STRING) | |
148 | { | |
149 | val = _dl_strtoul (strval, NULL); | |
150 | valp = &val; | |
151 | } | |
152 | else | |
153 | { | |
154 | cur->initialized = true; | |
155 | valp = strval; | |
156 | } | |
157 | do_tunable_update_val (cur, valp); | |
158 | } | |
159 | ||
160 | void | |
161 | __tunable_set_val (tunable_id_t id, void *valp) | |
162 | { | |
163 | tunable_t *cur = &tunable_list[id]; | |
164 | ||
165 | do_tunable_update_val (cur, valp); | |
166 | } | |
167 | ||
168 | #if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring | |
169 | /* Parse the tunable string TUNESTR and adjust it to drop any tunables that may | |
170 | be unsafe for AT_SECURE processes so that it can be used as the new | |
171 | environment variable value for GLIBC_TUNABLES. VALSTRING is the original | |
172 | environment variable string which we use to make NULL terminated values so | |
173 | that we don't have to allocate memory again for it. */ | |
174 | static void | |
175 | parse_tunables (char *tunestr, char *valstring) | |
176 | { | |
177 | if (tunestr == NULL || *tunestr == '\0') | |
178 | return; | |
179 | ||
180 | char *p = tunestr; | |
181 | ||
182 | while (true) | |
183 | { | |
184 | char *name = p; | |
185 | size_t len = 0; | |
186 | ||
187 | /* First, find where the name ends. */ | |
188 | while (p[len] != '=' && p[len] != ':' && p[len] != '\0') | |
189 | len++; | |
190 | ||
191 | /* If we reach the end of the string before getting a valid name-value | |
192 | pair, bail out. */ | |
193 | if (p[len] == '\0') | |
194 | return; | |
195 | ||
196 | /* We did not find a valid name-value pair before encountering the | |
197 | colon. */ | |
198 | if (p[len]== ':') | |
199 | { | |
200 | p += len + 1; | |
201 | continue; | |
202 | } | |
203 | ||
204 | p += len + 1; | |
205 | ||
206 | /* Take the value from the valstring since we need to NULL terminate it. */ | |
207 | char *value = &valstring[p - tunestr]; | |
208 | len = 0; | |
209 | ||
210 | while (p[len] != ':' && p[len] != '\0') | |
211 | len++; | |
212 | ||
213 | /* Add the tunable if it exists. */ | |
214 | for (size_t i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++) | |
215 | { | |
216 | tunable_t *cur = &tunable_list[i]; | |
217 | ||
218 | if (tunable_is_name (cur->name, name)) | |
219 | { | |
220 | /* If we are in a secure context (AT_SECURE) then ignore the tunable | |
221 | unless it is explicitly marked as secure. Tunable values take | |
222 | precendence over their envvar aliases. */ | |
223 | if (__libc_enable_secure) | |
224 | { | |
225 | if (cur->security_level == TUNABLE_SECLEVEL_SXID_ERASE) | |
226 | { | |
227 | if (p[len] == '\0') | |
228 | { | |
229 | /* Last tunable in the valstring. Null-terminate and | |
230 | return. */ | |
231 | *name = '\0'; | |
232 | return; | |
233 | } | |
234 | else | |
235 | { | |
236 | /* Remove the current tunable from the string. We do | |
237 | this by overwriting the string starting from NAME | |
238 | (which is where the current tunable begins) with | |
239 | the remainder of the string. We then have P point | |
240 | to NAME so that we continue in the correct | |
241 | position in the valstring. */ | |
242 | char *q = &p[len + 1]; | |
243 | p = name; | |
244 | while (*q != '\0') | |
245 | *name++ = *q++; | |
246 | name[0] = '\0'; | |
247 | len = 0; | |
248 | } | |
249 | } | |
250 | ||
251 | if (cur->security_level != TUNABLE_SECLEVEL_NONE) | |
252 | break; | |
253 | } | |
254 | ||
255 | value[len] = '\0'; | |
256 | tunable_initialize (cur, value); | |
257 | break; | |
258 | } | |
259 | } | |
260 | ||
261 | if (p[len] == '\0') | |
262 | return; | |
263 | else | |
264 | p += len + 1; | |
265 | } | |
266 | } | |
267 | #endif | |
268 | ||
269 | /* Enable the glibc.malloc.check tunable in SETUID/SETGID programs only when | |
270 | the system administrator has created the /etc/suid-debug file. This is a | |
271 | special case where we want to conditionally enable/disable a tunable even | |
272 | for setuid binaries. We use the special version of access() to avoid | |
273 | setting ERRNO, which is a TLS variable since TLS has not yet been set | |
274 | up. */ | |
275 | static inline void | |
276 | __always_inline | |
277 | maybe_enable_malloc_check (void) | |
278 | { | |
279 | tunable_id_t id = TUNABLE_ENUM_NAME (glibc, malloc, check); | |
280 | if (__libc_enable_secure && __access_noerrno ("/etc/suid-debug", F_OK) == 0) | |
281 | tunable_list[id].security_level = TUNABLE_SECLEVEL_NONE; | |
282 | } | |
283 | ||
284 | /* Initialize the tunables list from the environment. For now we only use the | |
285 | ENV_ALIAS to find values. Later we will also use the tunable names to find | |
286 | values. */ | |
287 | void | |
288 | __tunables_init (char **envp) | |
289 | { | |
290 | char *envname = NULL; | |
291 | char *envval = NULL; | |
292 | size_t len = 0; | |
293 | char **prev_envp = envp; | |
294 | ||
295 | maybe_enable_malloc_check (); | |
296 | ||
297 | while ((envp = get_next_env (envp, &envname, &len, &envval, | |
298 | &prev_envp)) != NULL) | |
299 | { | |
300 | #if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring | |
301 | if (tunable_is_name (GLIBC_TUNABLES, envname)) | |
302 | { | |
303 | char *new_env = tunables_strdup (envname); | |
304 | if (new_env != NULL) | |
305 | parse_tunables (new_env + len + 1, envval); | |
306 | /* Put in the updated envval. */ | |
307 | *prev_envp = new_env; | |
308 | continue; | |
309 | } | |
310 | #endif | |
311 | ||
312 | for (int i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++) | |
313 | { | |
314 | tunable_t *cur = &tunable_list[i]; | |
315 | ||
316 | /* Skip over tunables that have either been set already or should be | |
317 | skipped. */ | |
318 | if (cur->initialized || cur->env_alias == NULL) | |
319 | continue; | |
320 | ||
321 | const char *name = cur->env_alias; | |
322 | ||
323 | /* We have a match. Initialize and move on to the next line. */ | |
324 | if (tunable_is_name (name, envname)) | |
325 | { | |
326 | /* For AT_SECURE binaries, we need to check the security settings of | |
327 | the tunable and decide whether we read the value and also whether | |
328 | we erase the value so that child processes don't inherit them in | |
329 | the environment. */ | |
330 | if (__libc_enable_secure) | |
331 | { | |
332 | if (cur->security_level == TUNABLE_SECLEVEL_SXID_ERASE) | |
333 | { | |
334 | /* Erase the environment variable. */ | |
335 | char **ep = prev_envp; | |
336 | ||
337 | while (*ep != NULL) | |
338 | { | |
339 | if (tunable_is_name (name, *ep)) | |
340 | { | |
341 | char **dp = ep; | |
342 | ||
343 | do | |
344 | dp[0] = dp[1]; | |
345 | while (*dp++); | |
346 | } | |
347 | else | |
348 | ++ep; | |
349 | } | |
350 | /* Reset the iterator so that we read the environment again | |
351 | from the point we erased. */ | |
352 | envp = prev_envp; | |
353 | } | |
354 | ||
355 | if (cur->security_level != TUNABLE_SECLEVEL_NONE) | |
356 | continue; | |
357 | } | |
358 | ||
359 | tunable_initialize (cur, envval); | |
360 | break; | |
361 | } | |
362 | } | |
363 | } | |
364 | } | |
365 | ||
366 | /* Set the tunable value. This is called by the module that the tunable exists | |
367 | in. */ | |
368 | void | |
369 | __tunable_get_val (tunable_id_t id, void *valp, tunable_callback_t callback) | |
370 | { | |
371 | tunable_t *cur = &tunable_list[id]; | |
372 | ||
373 | switch (cur->type.type_code) | |
374 | { | |
375 | case TUNABLE_TYPE_UINT_64: | |
376 | { | |
377 | *((uint64_t *) valp) = (uint64_t) cur->val.numval; | |
378 | break; | |
379 | } | |
380 | case TUNABLE_TYPE_INT_32: | |
381 | { | |
382 | *((int32_t *) valp) = (int32_t) cur->val.numval; | |
383 | break; | |
384 | } | |
385 | case TUNABLE_TYPE_SIZE_T: | |
386 | { | |
387 | *((size_t *) valp) = (size_t) cur->val.numval; | |
388 | break; | |
389 | } | |
390 | case TUNABLE_TYPE_STRING: | |
391 | { | |
392 | *((const char **)valp) = cur->val.strval; | |
393 | break; | |
394 | } | |
395 | default: | |
396 | __builtin_unreachable (); | |
397 | } | |
398 | ||
399 | if (cur->initialized && callback != NULL) | |
400 | callback (&cur->val); | |
401 | } | |
402 | ||
403 | rtld_hidden_def (__tunable_get_val) |