1 /*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22 /*
23 * Copyright (c) 1989, 2010, Oracle and/or its affiliates. All rights reserved.
24 * Copyright 2016 Joyent, Inc.
25 */
26
27 /* Copyright (c) 1988 AT&T */
28 /* All Rights Reserved */
29
30 #pragma weak _putenv = putenv
31
32 #include "lint.h"
33 #include <mtlib.h>
34 #include <sys/types.h>
35 #include <thread.h>
36 #include <synch.h>
37 #include <stdlib.h>
38 #include <errno.h>
39 #include <string.h>
40 #include <atomic.h>
41
42 #define MIN_ENV_SIZE 128
43
44 extern const char **_environ;
45 extern void clean_env();
46
47 /*
48 * For performance and consistency reasons we expand the _environ list using
49 * the trusted "power of two, drop it on the floor" method. This allows for
50 * a lockless, single pass implementation of getenv(), yet the memory leak
51 * is bounded - in normal circumstances total wastage is never greater than
52 * 3x the space needed to hold any _environ list.
53 *
54 * The only abnormal circumstance is if an application modifies the _environ
55 * list pointer directly. Such an application does not conform to POSIX.1
56 * 2001. However, we also care about standards which did not foresee this
57 * issue. For this reason we keep a working copy of our notion of _environ in
58 * my_environ. If, when we are called upon to modify _environ, we ever detect
59 * a mismatch between _environ and my_environ we discard all our assumptions
60 * concerning the location and size of the _environ list. As an additional
61 * precaution we only ever update _environ once we have finished manipulating
62 * our working copy.
63 *
64 * The setenv() API is inherently leaky but we are completely at the mercy
65 * of the application.
66 *
67 * To pacify leak detectors we chain all allocations which are at risk of
68 * being leaked in either of the above two scenarios. chunk_list must only
69 * be updated under the protection of update_lock.
70 *
71 * Although we don't allocate the original _environ list it is likely that
72 * we will leak this too. Accordingly, we create a reference in initenv().
73 * However, we can't be held responsible for such leaks in abnormal (see
74 * above) circumstances.
75 */
76
77 typedef struct chunk {
78 struct chunk *next;
79 } chunk_t;
80
81 static mutex_t update_lock = DEFAULTMUTEX;
82 static const char **orig_environ = NULL;
83 static const char **my_environ = NULL;
84 static const char **environ_base = NULL;
85 static int environ_size = 0;
86 static int environ_gen = 0;
87 static int initenv_done = 0;
88 static chunk_t *chunk_list = NULL;
89
90 /*
91 * Compute the size an _environ list including the terminating NULL entry.
92 * This is the only way we have to determine the size of an _environ list
93 * we didn't allocate.
94 */
95 static int
envsize(const char ** e)96 envsize(const char **e)
97 {
98 int size;
99
100 if (e == NULL)
101 return (0);
102
103 for (size = 1; *e != NULL; e++)
104 size++;
105
106 return (size);
107 }
108
109 /*
110 * Initialization for the following scenarios:
111 * 1. The very first time we reference the _environ list we must call in the
112 * NLSPATH janitor, make a reference to the original _environ list to keep
113 * leak detectors happy, initialize my_environ and environ_base, and then
114 * compute environ_size.
115 * 2. Whenever we detect that someone else has hijacked _environ (something
116 * very abnormal) we need to reinitialize my_environ and environ_base,
117 * and then recompute environ_size.
118 *
119 * The local globals my_environ, environ_base and environ_size may be used
120 * by others only if initenv_done is true and only under the protection of
121 * update_lock. However, our callers, who must NOT be holding update_lock,
122 * may safely test initenv_done or my_environ against _environ just prior to
123 * calling us because we test these again whilst holding update_lock.
124 */
125 static void
initenv()126 initenv()
127 {
128 if ((my_environ != _environ) || !initenv_done) {
129 lmutex_lock(&update_lock);
130 if ((my_environ != _environ) || !initenv_done) {
131 if (!initenv_done) {
132 /* Call the NLSPATH janitor in. */
133 clean_env();
134
135 /* Pacify leak detectors in normal operation. */
136 orig_environ = _environ;
137 #ifdef __lint
138 my_environ = orig_environ;
139 #endif
140 }
141
142 my_environ = _environ;
143 environ_base = my_environ;
144 environ_size = envsize(environ_base);
145 membar_producer();
146 initenv_done = 1;
147 }
148 lmutex_unlock(&update_lock);
149 }
150 membar_consumer();
151 }
152
153 /*
154 * Search an _environ list for a particular entry. If name_only is set, then
155 * string must be the entry name only, and we return the value of the first
156 * match. Otherwise, string must be of the form "name=value", and we return
157 * the address of the first matching entry.
158 */
159 static const char **
findenv(const char ** e,const char * string,int name_only,char ** value)160 findenv(const char **e, const char *string, int name_only, char **value)
161 {
162 char target;
163 const char *s1;
164 const char *s2;
165
166 *value = NULL;
167
168 if (e == NULL)
169 return (NULL);
170
171 target = name_only ? '\0' : '=';
172
173 for (; (s2 = *e) != NULL; e++) {
174 s1 = string;
175
176 /* Fast comparison for first char. */
177 if (*s1 != *s2)
178 continue;
179
180 /* Slow comparison for rest of string. */
181 while (*s1 == *s2 && *s2 != '=') {
182 s1++;
183 s2++;
184 }
185
186 if (*s1 == target && *s2 == '=') {
187 *value = (char *)s2 + 1;
188 return (e);
189 }
190 }
191 return (NULL);
192 }
193
194 /*
195 * Common code for putenv() and setenv(). We support the lockless getenv()
196 * by inserting new entries at the bottom of the list, and by growing the
197 * list using the trusted "power of two, drop it on the floor" method. We
198 * use a lock (update_lock) to protect all updates to the _environ list, but
199 * we are obliged to release this lock whenever we call malloc() or free().
200 * A generation number (environ_gen) is bumped whenever names are added to,
201 * or removed from, the _environ list so that we can detect collisions with
202 * other updaters.
203 *
204 * Return values
205 * 0 : success
206 * -1 : with errno set
207 * -2 : an entry already existed and overwrite was zero
208 */
209 static int
addtoenv(char * string,int overwrite)210 addtoenv(char *string, int overwrite)
211 {
212 char *value;
213 const char **p;
214 chunk_t *new_chunk;
215 const char **new_environ;
216 const char **new_base;
217 int new_size;
218 int old_gen;
219
220 initenv();
221
222 lmutex_lock(&update_lock);
223
224 for (;;) {
225 /*
226 * If the name already exists just overwrite the existing
227 * entry -- except when we were called by setenv() without
228 * the overwrite flag.
229 */
230 if ((p = findenv(my_environ, string, 0, &value)) != NULL) {
231 if (overwrite) {
232 /*
233 * Replace the value in situ. No name was
234 * added, so there is no need to bump the
235 * generation number.
236 */
237 *p = string;
238 lmutex_unlock(&update_lock);
239 return (0);
240 } else {
241 /* No change. */
242 lmutex_unlock(&update_lock);
243 return (-2);
244 }
245 }
246
247 /* Try to insert the new entry at the bottom of the list. */
248 if (environ_base < my_environ) {
249 /*
250 * The new value must be visible before we decrement
251 * the _environ list pointer.
252 */
253 my_environ[-1] = string;
254 membar_producer();
255 my_environ--;
256 _environ = my_environ;
257
258 /*
259 * We've added a name, so bump the generation number.
260 */
261 environ_gen++;
262
263 lmutex_unlock(&update_lock);
264 return (0);
265 }
266
267 /*
268 * There is no room. Attempt to allocate a new _environ list
269 * which is at least double the size of the current one. See
270 * comment above concerning locking and malloc() etc.
271 */
272 new_size = environ_size * 2;
273 if (new_size < MIN_ENV_SIZE)
274 new_size = MIN_ENV_SIZE;
275
276 old_gen = environ_gen;
277 lmutex_unlock(&update_lock);
278
279 new_chunk = malloc(sizeof (chunk_t) +
280 new_size * sizeof (char *));
281 if (new_chunk == NULL) {
282 errno = ENOMEM;
283 return (-1);
284 }
285
286 lmutex_lock(&update_lock);
287
288 /*
289 * If no other thread added or removed names while the lock
290 * was dropped, it is time to break out of this loop.
291 */
292 if (environ_gen == old_gen)
293 break;
294
295 /*
296 * At least one name has been added or removed, so we need to
297 * try again. It is very likely that we will find sufficient
298 * space the next time around.
299 */
300 lmutex_unlock(&update_lock);
301 free(new_chunk);
302 lmutex_lock(&update_lock);
303 }
304
305 /* Add the new chunk to chunk_list to hide potential future leak. */
306 new_chunk->next = chunk_list;
307 chunk_list = new_chunk;
308
309 /* Copy the old _environ list into the top of the new _environ list. */
310 new_base = (const char **)(new_chunk + 1);
311 new_environ = &new_base[(new_size - 1) - environ_size];
312 (void) memcpy(new_environ, my_environ, environ_size * sizeof (char *));
313
314 /* Insert the new entry at the bottom of the new _environ list. */
315 new_environ[-1] = string;
316 new_environ--;
317
318 /* Ensure that the new _environ list is visible to all. */
319 membar_producer();
320
321 /* Make the switch (dropping the old _environ list on the floor). */
322 environ_base = new_base;
323 my_environ = new_environ;
324 _environ = my_environ;
325 environ_size = new_size;
326
327 /* We've added a name, so bump the generation number. */
328 environ_gen++;
329
330 lmutex_unlock(&update_lock);
331 return (0);
332 }
333
334 /*
335 * All the work for putenv() is done in addtoenv().
336 */
337 int
putenv(char * string)338 putenv(char *string)
339 {
340 /*
341 * Historically a call to putenv() with no '=' in the string would work
342 * great until someone called getenv() on that particular environment
343 * variable again. As we've always treated this as valid, rather than
344 * teaching the rest of the environment code how to handle something
345 * without an '=' sign, it instead just calls unsetenv().
346 */
347 if (strchr(string, '=') == NULL)
348 return (unsetenv(string));
349
350 return (addtoenv(string, 1));
351 }
352
353 /*
354 * setenv() is a little more complex than putenv() because we have to allocate
355 * and construct an _environ entry on behalf of the caller. The bulk of the
356 * work is still done in addtoenv().
357 */
358
359 int
setenv(const char * envname,const char * envval,int overwrite)360 setenv(const char *envname, const char *envval, int overwrite)
361 {
362 chunk_t *new_chunk;
363 char *new_string;
364 size_t name_len;
365 size_t val_len;
366 int res;
367
368 if (envname == NULL || *envname == 0 || strchr(envname, '=') != NULL) {
369 errno = EINVAL;
370 return (-1);
371 }
372
373 name_len = strlen(envname);
374 val_len = strlen(envval);
375
376 new_chunk = malloc(sizeof (chunk_t) + name_len + val_len + 2);
377 if (new_chunk == NULL) {
378 errno = ENOMEM;
379 return (-1);
380 }
381 new_string = (char *)(new_chunk + 1);
382
383 (void) memcpy(new_string, envname, name_len);
384 new_string[name_len] = '=';
385 (void) memcpy(new_string + name_len + 1, envval, val_len);
386 new_string[name_len + 1 + val_len] = 0;
387
388 if ((res = addtoenv(new_string, overwrite)) < 0) {
389 free(new_chunk);
390 if (res == -2) {
391 /* The name already existed, but not an error. */
392 return (0);
393 } else {
394 /* i.e. res == -1 which means only one thing. */
395 errno = ENOMEM;
396 return (-1);
397 }
398 }
399
400 /* Hide potential leak of new_string. */
401 lmutex_lock(&update_lock);
402 new_chunk->next = chunk_list;
403 chunk_list = new_chunk;
404 lmutex_unlock(&update_lock);
405
406 return (0);
407 }
408
409 /*
410 * unsetenv() is tricky because we need to compress the _environ list in a way
411 * which supports a lockless getenv(). The approach here is to move the first
412 * entry from the enrivon list into the space occupied by the entry to be
413 * deleted, and then to increment _environ. This has the added advantage of
414 * making _any_ incremental linear search of the _environ list consistent (i.e.
415 * we will not break any naughty apps which read the list without our help).
416 */
417 int
unsetenv(const char * name)418 unsetenv(const char *name)
419 {
420 const char **p;
421 char *value;
422
423 if (name == NULL || *name == 0 || strchr(name, '=') != NULL) {
424 errno = EINVAL;
425 return (-1);
426 }
427
428 initenv();
429
430 lmutex_lock(&update_lock);
431
432 /*
433 * Find the target, overwrite it with the first entry, increment the
434 * _environ pointer.
435 */
436 if ((p = findenv(my_environ, name, 1, &value)) != NULL) {
437 /* Overwrite target with the first entry. */
438 *p = my_environ[0];
439
440 /* Ensure that the moved entry is visible to all. */
441 membar_producer();
442
443 /* Shrink the _environ list. */
444 my_environ++;
445 _environ = my_environ;
446
447 /* Make sure addtoenv() knows that we've removed a name. */
448 environ_gen++;
449 }
450
451 lmutex_unlock(&update_lock);
452 return (0);
453 }
454
455 /*
456 * Dump entire environment.
457 */
458 int
clearenv(void)459 clearenv(void)
460 {
461 /*
462 * Just drop the entire environment list on the floor, as it
463 * would be non-trivial to try and free the used memory.
464 */
465 static const char *nullp = NULL;
466
467 lmutex_lock(&update_lock);
468 _environ = &nullp;
469 my_environ = NULL;
470 environ_base = NULL;
471 environ_size = 0;
472 environ_gen++;
473 membar_producer();
474 lmutex_unlock(&update_lock);
475
476 return (0);
477 }
478
479 /*
480 * At last, a lockless implementation of getenv()!
481 */
482 char *
getenv(const char * name)483 getenv(const char *name)
484 {
485 char *value;
486
487 initenv();
488
489 if (findenv(_environ, name, 1, &value) != NULL)
490 return (value);
491
492 return (NULL);
493 }
494