linker_environ.c revision 16084168111cd7d2ac8a6b92e6fa6df5696928a5 
1/*
2 * Copyright (C) 2010 The Android Open Source Project
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 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28#include "linker_environ.h"
29#include <stddef.h>
30
31static char** _envp;
32
33/* Returns 1 if 'str' points to a valid environment variable definition.
34 * For now, we check that:
35 *  - It is smaller than MAX_ENV_LEN (to detect non-zero terminated strings)
36 *  - It contains at least one equal sign that is not the first character
37 */
38static int
39_is_valid_definition(const char*  str)
40{
41    int   pos = 0;
42    int   first_equal_pos = -1;
43
44    /* According to its sources, the kernel uses 32*PAGE_SIZE by default
45     * as the maximum size for an env. variable definition.
46     */
47    const int MAX_ENV_LEN = 32*4096;
48
49    if (str == NULL)
50        return 0;
51
52    /* Parse the string, looking for the first '=' there, and its size */
53    do {
54        if (str[pos] == '\0')
55            break;
56        if (str[pos] == '=' && first_equal_pos < 0)
57            first_equal_pos = pos;
58        pos++;
59    } while (pos < MAX_ENV_LEN);
60
61    if (pos >= MAX_ENV_LEN)  /* Too large */
62        return 0;
63
64    if (first_equal_pos < 1)  /* No equal sign, or it is the first character */
65        return 0;
66
67    return 1;
68}
69
70unsigned*
71linker_env_init(unsigned* vecs)
72{
73    /* Store environment pointer - can't be NULL */
74    _envp = (char**) vecs;
75
76    /* Skip over all definitions */
77    while (vecs[0] != 0)
78        vecs++;
79    /* The end of the environment block is marked by two NULL pointers */
80    vecs++;
81
82    /* As a sanity check, we're going to remove all invalid variable
83     * definitions from the environment array.
84     */
85    {
86        char** readp  = _envp;
87        char** writep = _envp;
88        for ( ; readp[0] != NULL; readp++ ) {
89            if (!_is_valid_definition(readp[0]))
90                continue;
91            writep[0] = readp[0];
92            writep++;
93        }
94        writep[0] = NULL;
95    }
96
97    /* Return the address of the aux vectors table */
98    return vecs;
99}
100
101/* Check if the environment variable definition at 'envstr'
102 * starts with '<name>=', and if so return the address of the
103 * first character after the equal sign. Otherwise return NULL.
104 */
105static char*
106env_match(char* envstr, const char* name)
107{
108    size_t  cnt = 0;
109
110    while (envstr[cnt] == name[cnt] && name[cnt] != '\0')
111        cnt++;
112
113    if (name[cnt] == '\0' && envstr[cnt] == '=')
114        return envstr + cnt + 1;
115
116    return NULL;
117}
118
119#define MAX_ENV_LEN  (16*4096)
120
121const char*
122linker_env_get(const char* name)
123{
124    char** readp = _envp;
125
126    if (name == NULL || name[0] == '\0')
127        return NULL;
128
129    for ( ; readp[0] != NULL; readp++ ) {
130        char* val = env_match(readp[0], name);
131        if (val != NULL) {
132            /* Return NULL for empty strings, or if it is too large */
133            if (val[0] == '\0')
134                val = NULL;
135            return val;
136        }
137    }
138    return NULL;
139}
140
141
142void
143linker_env_unset(const char* name)
144{
145    char**  readp = _envp;
146    char**  writep = readp;
147
148    if (name == NULL || name[0] == '\0')
149        return;
150
151    for ( ; readp[0] != NULL; readp++ ) {
152        if (env_match(readp[0], name))
153            continue;
154        writep[0] = readp[0];
155        writep++;
156    }
157    /* end list with a NULL */
158    writep[0] = NULL;
159}
160
161
162
163/* Remove unsafe environment variables. This should be used when
164 * running setuid programs. */
165void
166linker_env_secure(void)
167{
168    /* The same list than GLibc at this point */
169    static const char* const unsec_vars[] = {
170        "GCONV_PATH",
171        "GETCONF_DIR",
172        "HOSTALIASES",
173        "LD_AUDIT",
174        "LD_DEBUG",
175        "LD_DEBUG_OUTPUT",
176        "LD_DYNAMIC_WEAK",
177        "LD_LIBRARY_PATH",
178        "LD_ORIGIN_PATH",
179        "LD_PRELOAD",
180        "LD_PROFILE",
181        "LD_SHOW_AUXV",
182        "LD_USE_LOAD_BIAS",
183        "LOCALDOMAIN",
184        "LOCPATH",
185        "MALLOC_TRACE",
186        "MALLOC_CHECK_",
187        "NIS_PATH",
188        "NLSPATH",
189        "RESOLV_HOST_CONF",
190        "RES_OPTIONS",
191        "TMPDIR",
192        "TZDIR",
193        "LD_AOUT_LIBRARY_PATH",
194        "LD_AOUT_PRELOAD",
195        NULL
196    };
197
198    int count;
199    for (count = 0; unsec_vars[count] != NULL; count++) {
200        linker_env_unset(unsec_vars[count]);
201    }
202}
203