getenv.c revision 200191 
1/*-
2 * Copyright (c) 2007-2009 Sean C. Farley <scf@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer,
10 *    without modification, immediately at the beginning of the file.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include <sys/cdefs.h>
28__FBSDID("$FreeBSD: head/lib/libc/stdlib/getenv.c 200191 2009-12-06 23:27:24Z scf $");
29
30
31#include "namespace.h"
32#include <sys/types.h>
33#include <errno.h>
34#include <stdbool.h>
35#include <stddef.h>
36#include <stdlib.h>
37#include <string.h>
38#include <unistd.h>
39#include "un-namespace.h"
40
41
42static const char CorruptEnvFindMsg[] = "environment corrupt; unable to find ";
43static const char CorruptEnvValueMsg[] =
44    "environment corrupt; missing value for ";
45
46
47/*
48 * Standard environ.  environ variable is exposed to entire process.
49 *
50 *	origEnviron:	Upon cleanup on unloading of library or failure, this
51 *			allows environ to return to as it was before.
52 *	environSize:	Number of variables environ can hold.  Can only
53 *			increase.
54 *	intEnviron:	Internally-built environ.  Exposed via environ during
55 *			(re)builds of the environment.
56 */
57extern char **environ;
58static char **origEnviron;
59static char **intEnviron = NULL;
60static int environSize = 0;
61
62/*
63 * Array of environment variables built from environ.  Each element records:
64 *	name:		Pointer to name=value string
65 *	name length:	Length of name not counting '=' character
66 *	value:		Pointer to value within same string as name
67 *	value size:	Size (not length) of space for value not counting the
68 *			nul character
69 *	active state:	true/false value to signify whether variable is active.
70 *			Useful since multiple variables with the same name can
71 *			co-exist.  At most, one variable can be active at any
72 *			one time.
73 *	putenv:		Created from putenv() call.  This memory must not be
74 *			reused.
75 */
76static struct envVars {
77	size_t nameLen;
78	size_t valueSize;
79	char *name;
80	char *value;
81	bool active;
82	bool putenv;
83} *envVars = NULL;
84
85/*
86 * Environment array information.
87 *
88 *	envActive:	Number of active variables in array.
89 *	envVarsSize:	Size of array.
90 *	envVarsTotal:	Number of total variables in array (active or not).
91 */
92static int envActive = 0;
93static int envVarsSize = 0;
94static int envVarsTotal = 0;
95
96
97/* Deinitialization of new environment. */
98static void __attribute__ ((destructor)) __clean_env_destructor(void);
99
100
101/*
102 * A simple version of warnx() to avoid the bloat of including stdio in static
103 * binaries.
104 */
105static void
106__env_warnx(const char *msg, const char *name, size_t nameLen)
107{
108	static const char nl[] = "\n";
109	static const char progSep[] = ": ";
110
111	_write(STDERR_FILENO, _getprogname(), strlen(_getprogname()));
112	_write(STDERR_FILENO, progSep, sizeof(progSep) - 1);
113	_write(STDERR_FILENO, msg, strlen(msg));
114	_write(STDERR_FILENO, name, nameLen);
115	_write(STDERR_FILENO, nl, sizeof(nl) - 1);
116
117	return;
118}
119
120
121/*
122 * Inline strlen() for performance.  Also, perform check for an equals sign.
123 * Cheaper here than peforming a strchr() later.
124 */
125static inline size_t
126__strleneq(const char *str)
127{
128	const char *s;
129
130	for (s = str; *s != '\0'; ++s)
131		if (*s == '=')
132			return (0);
133
134	return (s - str);
135}
136
137
138/*
139 * Comparison of an environment name=value to a name.
140 */
141static inline bool
142strncmpeq(const char *nameValue, const char *name, size_t nameLen)
143{
144	if (strncmp(nameValue, name, nameLen) == 0 && nameValue[nameLen] == '=')
145		return (true);
146
147	return (false);
148}
149
150
151/*
152 * Using environment, returns pointer to value associated with name, if any,
153 * else NULL.  If the onlyActive flag is set to true, only variables that are
154 * active are returned else all are.
155 */
156static inline char *
157__findenv(const char *name, size_t nameLen, int *envNdx, bool onlyActive)
158{
159	int ndx;
160
161	/*
162	 * Find environment variable from end of array (more likely to be
163	 * active).  A variable created by putenv is always active, or it is not
164	 * tracked in the array.
165	 */
166	for (ndx = *envNdx; ndx >= 0; ndx--)
167		if (envVars[ndx].putenv) {
168			if (strncmpeq(envVars[ndx].name, name, nameLen)) {
169				*envNdx = ndx;
170				return (envVars[ndx].name + nameLen +
171				    sizeof ("=") - 1);
172			}
173		} else if ((!onlyActive || envVars[ndx].active) &&
174		    (envVars[ndx].nameLen == nameLen &&
175		    strncmpeq(envVars[ndx].name, name, nameLen))) {
176			*envNdx = ndx;
177			return (envVars[ndx].value);
178		}
179
180	return (NULL);
181}
182
183
184/*
185 * Using environ, returns pointer to value associated with name, if any, else
186 * NULL.  Used on the original environ passed into the program.
187 */
188static char *
189__findenv_environ(const char *name, size_t nameLen)
190{
191	int envNdx;
192
193	/* Find variable within environ. */
194	for (envNdx = 0; environ[envNdx] != NULL; envNdx++)
195		if (strncmpeq(environ[envNdx], name, nameLen))
196			return (&(environ[envNdx][nameLen + sizeof("=") - 1]));
197
198	return (NULL);
199}
200
201
202/*
203 * Remove variable added by putenv() from variable tracking array.
204 */
205static void
206__remove_putenv(int envNdx)
207{
208	envVarsTotal--;
209	if (envVarsTotal > envNdx)
210		memmove(&(envVars[envNdx]), &(envVars[envNdx + 1]),
211		    (envVarsTotal - envNdx) * sizeof (*envVars));
212	memset(&(envVars[envVarsTotal]), 0, sizeof (*envVars));
213
214	return;
215}
216
217
218/*
219 * Deallocate the environment built from environ as well as environ then set
220 * both to NULL.  Eases debugging of memory leaks.
221 */
222static void
223__clean_env(bool freeVars)
224{
225	int envNdx;
226
227	/* Deallocate environment and environ if created by *env(). */
228	if (envVars != NULL) {
229		for (envNdx = envVarsTotal - 1; envNdx >= 0; envNdx--)
230			/* Free variables or deactivate them. */
231			if (envVars[envNdx].putenv) {
232				if (!freeVars)
233					__remove_putenv(envNdx);
234			} else {
235				if (freeVars)
236					free(envVars[envNdx].name);
237				else
238					envVars[envNdx].active = false;
239			}
240		if (freeVars) {
241			free(envVars);
242			envVars = NULL;
243		} else
244			envActive = 0;
245
246		/* Restore original environ if it has not updated by program. */
247		if (origEnviron != NULL) {
248			if (environ == intEnviron)
249				environ = origEnviron;
250			free(intEnviron);
251			intEnviron = NULL;
252			environSize = 0;
253		}
254	}
255
256	return;
257}
258
259
260/*
261 * Using the environment, rebuild the environ array for use by other C library
262 * calls that depend upon it.
263 */
264static int
265__rebuild_environ(int newEnvironSize)
266{
267	char **tmpEnviron;
268	int envNdx;
269	int environNdx;
270	int tmpEnvironSize;
271
272	/* Resize environ. */
273	if (newEnvironSize > environSize) {
274		tmpEnvironSize = newEnvironSize * 2;
275		tmpEnviron = realloc(intEnviron, sizeof (*intEnviron) *
276		    (tmpEnvironSize + 1));
277		if (tmpEnviron == NULL)
278			return (-1);
279		environSize = tmpEnvironSize;
280		intEnviron = tmpEnviron;
281	}
282	envActive = newEnvironSize;
283
284	/* Assign active variables to environ. */
285	for (envNdx = envVarsTotal - 1, environNdx = 0; envNdx >= 0; envNdx--)
286		if (envVars[envNdx].active)
287			intEnviron[environNdx++] = envVars[envNdx].name;
288	intEnviron[environNdx] = NULL;
289
290	/* Always set environ which may have been replaced by program. */
291	environ = intEnviron;
292
293	return (0);
294}
295
296
297/*
298 * Enlarge new environment.
299 */
300static inline bool
301__enlarge_env(void)
302{
303	int newEnvVarsSize;
304	struct envVars *tmpEnvVars;
305
306	envVarsTotal++;
307	if (envVarsTotal > envVarsSize) {
308		newEnvVarsSize = envVarsTotal * 2;
309		tmpEnvVars = realloc(envVars, sizeof (*envVars) *
310		    newEnvVarsSize);
311		if (tmpEnvVars == NULL) {
312			envVarsTotal--;
313			return (false);
314		}
315		envVarsSize = newEnvVarsSize;
316		envVars = tmpEnvVars;
317	}
318
319	return (true);
320}
321
322
323/*
324 * Using environ, build an environment for use by standard C library calls.
325 */
326static int
327__build_env(void)
328{
329	char **env;
330	int activeNdx;
331	int envNdx;
332	int savedErrno;
333	size_t nameLen;
334
335	/* Check for non-existant environment. */
336	if (environ == NULL || environ[0] == NULL)
337		return (0);
338
339	/* Count environment variables. */
340	for (env = environ, envVarsTotal = 0; *env != NULL; env++)
341		envVarsTotal++;
342	envVarsSize = envVarsTotal * 2;
343
344	/* Create new environment. */
345	envVars = calloc(1, sizeof (*envVars) * envVarsSize);
346	if (envVars == NULL)
347		goto Failure;
348
349	/* Copy environ values and keep track of them. */
350	for (envNdx = envVarsTotal - 1; envNdx >= 0; envNdx--) {
351		envVars[envNdx].putenv = false;
352		envVars[envNdx].name =
353		    strdup(environ[envVarsTotal - envNdx - 1]);
354		if (envVars[envNdx].name == NULL)
355			goto Failure;
356		envVars[envNdx].value = strchr(envVars[envNdx].name, '=');
357		if (envVars[envNdx].value != NULL) {
358			envVars[envNdx].value++;
359			envVars[envNdx].valueSize =
360			    strlen(envVars[envNdx].value);
361		} else {
362			__env_warnx(CorruptEnvValueMsg, envVars[envNdx].name,
363			    strlen(envVars[envNdx].name));
364			continue;
365		}
366
367		/*
368		 * Find most current version of variable to make active.  This
369		 * will prevent multiple active variables from being created
370		 * during this initialization phase.
371		 */
372		nameLen = envVars[envNdx].value - envVars[envNdx].name - 1;
373		envVars[envNdx].nameLen = nameLen;
374		activeNdx = envVarsTotal - 1;
375		if (__findenv(envVars[envNdx].name, nameLen, &activeNdx,
376		    false) == NULL) {
377			__env_warnx(CorruptEnvFindMsg, envVars[envNdx].name,
378			    nameLen);
379			continue;
380		}
381		envVars[activeNdx].active = true;
382	}
383
384	/* Create a new environ. */
385	origEnviron = environ;
386	environ = NULL;
387	if (__rebuild_environ(envVarsTotal) == 0)
388		return (0);
389
390Failure:
391	savedErrno = errno;
392	__clean_env(true);
393	errno = savedErrno;
394
395	return (-1);
396}
397
398
399/*
400 * Destructor function with default argument to __clean_env().
401 */
402static void
403__clean_env_destructor(void)
404{
405	__clean_env(true);
406
407	return;
408}
409
410
411/*
412 * Returns the value of a variable or NULL if none are found.
413 */
414char *
415getenv(const char *name)
416{
417	int envNdx;
418	size_t nameLen;
419
420	/* Check for malformed name. */
421	if (name == NULL || (nameLen = __strleneq(name)) == 0) {
422		errno = EINVAL;
423		return (NULL);
424	}
425
426	/*
427	 * Variable search order:
428	 * 1. Check for an empty environ.  This allows an application to clear
429	 *    the environment.
430	 * 2. Search the external environ array.
431	 * 3. Search the internal environment.
432	 *
433	 * Since malloc() depends upon getenv(), getenv() must never cause the
434	 * internal environment storage to be generated.
435	 */
436	if (environ == NULL || environ[0] == NULL)
437		return (NULL);
438	else if (envVars == NULL || environ != intEnviron)
439		return (__findenv_environ(name, nameLen));
440	else {
441		envNdx = envVarsTotal - 1;
442		return (__findenv(name, nameLen, &envNdx, true));
443	}
444}
445
446
447/*
448 * Set the value of a variable.  Older settings are labeled as inactive.  If an
449 * older setting has enough room to store the new value, it will be reused.  No
450 * previous variables are ever freed here to avoid causing a segmentation fault
451 * in a user's code.
452 *
453 * The variables nameLen and valueLen are passed into here to allow the caller
454 * to calculate the length by means besides just strlen().
455 */
456static int
457__setenv(const char *name, size_t nameLen, const char *value, int overwrite)
458{
459	bool reuse;
460	char *env;
461	int envNdx;
462	int newEnvActive;
463	size_t valueLen;
464
465	/* Find existing environment variable large enough to use. */
466	envNdx = envVarsTotal - 1;
467	newEnvActive = envActive;
468	valueLen = strlen(value);
469	reuse = false;
470	if (__findenv(name, nameLen, &envNdx, false) != NULL) {
471		/* Deactivate entry if overwrite is allowed. */
472		if (envVars[envNdx].active) {
473			if (overwrite == 0)
474				return (0);
475			envVars[envNdx].active = false;
476			newEnvActive--;
477		}
478
479		/* putenv() created variable cannot be reused. */
480		if (envVars[envNdx].putenv)
481			__remove_putenv(envNdx);
482
483		/* Entry is large enough to reuse. */
484		else if (envVars[envNdx].valueSize >= valueLen)
485			reuse = true;
486	}
487
488	/* Create new variable if none was found of sufficient size. */
489	if (! reuse) {
490		/* Enlarge environment. */
491		envNdx = envVarsTotal;
492		if (!__enlarge_env())
493			return (-1);
494
495		/* Create environment entry. */
496		envVars[envNdx].name = malloc(nameLen + sizeof ("=") +
497		    valueLen);
498		if (envVars[envNdx].name == NULL) {
499			envVarsTotal--;
500			return (-1);
501		}
502		envVars[envNdx].nameLen = nameLen;
503		envVars[envNdx].valueSize = valueLen;
504
505		/* Save name of name/value pair. */
506		env = stpcpy(envVars[envNdx].name, name);
507		if ((envVars[envNdx].name)[nameLen] != '=')
508			env = stpcpy(env, "=");
509	}
510	else
511		env = envVars[envNdx].value;
512
513	/* Save value of name/value pair. */
514	strcpy(env, value);
515	envVars[envNdx].value = env;
516	envVars[envNdx].active = true;
517	newEnvActive++;
518
519	/* No need to rebuild environ if an active variable was reused. */
520	if (reuse && newEnvActive == envActive)
521		return (0);
522	else
523		return (__rebuild_environ(newEnvActive));
524}
525
526
527/*
528 * If the program attempts to replace the array of environment variables
529 * (environ) environ or sets the first varible to NULL, then deactivate all
530 * variables and merge in the new list from environ.
531 */
532static int
533__merge_environ(void)
534{
535	char **env;
536	char *equals;
537
538	/*
539	 * Internally-built environ has been replaced or cleared (detected by
540	 * using the count of active variables against a NULL as the first value
541	 * in environ).  Clean up everything.
542	 */
543	if (intEnviron != NULL && (environ != intEnviron || (envActive > 0 &&
544	    environ[0] == NULL))) {
545		/* Deactivate all environment variables. */
546		if (envActive > 0) {
547			origEnviron = NULL;
548			__clean_env(false);
549		}
550
551		/*
552		 * Insert new environ into existing, yet deactivated,
553		 * environment array.
554		 */
555		origEnviron = environ;
556		if (origEnviron != NULL)
557			for (env = origEnviron; *env != NULL; env++) {
558				if ((equals = strchr(*env, '=')) == NULL) {
559					__env_warnx(CorruptEnvValueMsg, *env,
560					    strlen(*env));
561					continue;
562				}
563				if (__setenv(*env, equals - *env, equals + 1,
564				    1) == -1)
565					return (-1);
566			}
567	}
568
569	return (0);
570}
571
572
573/*
574 * The exposed setenv() that peforms a few tests before calling the function
575 * (__setenv()) that does the actual work of inserting a variable into the
576 * environment.
577 */
578int
579setenv(const char *name, const char *value, int overwrite)
580{
581	size_t nameLen;
582
583	/* Check for malformed name. */
584	if (name == NULL || (nameLen = __strleneq(name)) == 0) {
585		errno = EINVAL;
586		return (-1);
587	}
588
589	/* Initialize environment. */
590	if (__merge_environ() == -1 || (envVars == NULL && __build_env() == -1))
591		return (-1);
592
593	return (__setenv(name, nameLen, value, overwrite));
594}
595
596
597/*
598 * Insert a "name=value" string into the environment.  Special settings must be
599 * made to keep setenv() from reusing this memory block and unsetenv() from
600 * allowing it to be tracked.
601 */
602int
603putenv(char *string)
604{
605	char *equals;
606	int envNdx;
607	int newEnvActive;
608	size_t nameLen;
609
610	/* Check for malformed argument. */
611	if (string == NULL || (equals = strchr(string, '=')) == NULL ||
612	    (nameLen = equals - string) == 0) {
613		errno = EINVAL;
614		return (-1);
615	}
616
617	/* Initialize environment. */
618	if (__merge_environ() == -1 || (envVars == NULL && __build_env() == -1))
619		return (-1);
620
621	/* Deactivate previous environment variable. */
622	envNdx = envVarsTotal - 1;
623	newEnvActive = envActive;
624	if (__findenv(string, nameLen, &envNdx, true) != NULL) {
625		/* Reuse previous putenv slot. */
626		if (envVars[envNdx].putenv) {
627			envVars[envNdx].name = string;
628			return (__rebuild_environ(envActive));
629		} else {
630			newEnvActive--;
631			envVars[envNdx].active = false;
632		}
633	}
634
635	/* Enlarge environment. */
636	envNdx = envVarsTotal;
637	if (!__enlarge_env())
638		return (-1);
639
640	/* Create environment entry. */
641	envVars[envNdx].name = string;
642	envVars[envNdx].nameLen = -1;
643	envVars[envNdx].value = NULL;
644	envVars[envNdx].valueSize = -1;
645	envVars[envNdx].putenv = true;
646	envVars[envNdx].active = true;
647	newEnvActive++;
648
649	return (__rebuild_environ(newEnvActive));
650}
651
652
653/*
654 * Unset variable with the same name by flagging it as inactive.  No variable is
655 * ever freed.
656 */
657int
658unsetenv(const char *name)
659{
660	int envNdx;
661	size_t nameLen;
662
663	/* Check for malformed name. */
664	if (name == NULL || (nameLen = __strleneq(name)) == 0) {
665		errno = EINVAL;
666		return (-1);
667	}
668
669	/* Initialize environment. */
670	if (__merge_environ() == -1 || (envVars == NULL && __build_env() == -1))
671		return (-1);
672
673	/* Deactivate specified variable. */
674	envNdx = envVarsTotal - 1;
675	if (__findenv(name, nameLen, &envNdx, true) != NULL) {
676		envVars[envNdx].active = false;
677		if (envVars[envNdx].putenv)
678			__remove_putenv(envNdx);
679		__rebuild_environ(envActive - 1);
680	}
681
682	return (0);
683}
684