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
31 static 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 */
38 static int
_is_valid_definition(const char * str)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
70 unsigned*
linker_env_init(unsigned * vecs)71 linker_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 */
105 static char*
env_match(char * envstr,const char * name)106 env_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
121 const char*
linker_env_get(const char * name)122 linker_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
142 void
linker_env_unset(const char * name)143 linker_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. */
165 void
linker_env_secure(void)166 linker_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