| /* |
| * Copyright (C) 2010 The Android Open Source Project |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * * Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS |
| * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED |
| * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, |
| * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT |
| * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| * SUCH DAMAGE. |
| */ |
| |
| #include "linker_environ.h" |
| |
| #include <linux/auxvec.h> |
| #include <stddef.h> |
| #include <stdlib.h> |
| #include <unistd.h> |
| |
| static char** _envp; |
| static bool _AT_SECURE_value = true; |
| |
| bool get_AT_SECURE() { |
| return _AT_SECURE_value; |
| } |
| |
| /* Returns 1 if 'str' points to a valid environment variable definition. |
| * For now, we check that: |
| * - It is smaller than MAX_ENV_LEN (to detect non-zero terminated strings) |
| * - It contains at least one equal sign that is not the first character |
| */ |
| static int _is_valid_definition(const char* str) { |
| int pos = 0; |
| int first_equal_pos = -1; |
| |
| // According to its sources, the kernel uses 32*PAGE_SIZE by default |
| // as the maximum size for an env. variable definition. |
| const int MAX_ENV_LEN = 32*4096; |
| |
| if (str == NULL) { |
| return 0; |
| } |
| |
| // Parse the string, looking for the first '=' there, and its size. |
| while (pos < MAX_ENV_LEN) { |
| if (str[pos] == '\0') { |
| break; |
| } |
| if (str[pos] == '=' && first_equal_pos < 0) { |
| first_equal_pos = pos; |
| } |
| pos++; |
| } |
| |
| if (pos >= MAX_ENV_LEN) { |
| return 0; // Too large. |
| } |
| |
| if (first_equal_pos < 1) { |
| return 0; // No equals sign, or it's the first character. |
| } |
| |
| return 1; |
| } |
| |
| static void __init_AT_SECURE(unsigned* auxv) { |
| // Check auxv for AT_SECURE first to see if program is setuid, setgid, |
| // has file caps, or caused a SELinux/AppArmor domain transition. |
| for (unsigned* v = auxv; v[0]; v += 2) { |
| if (v[0] == AT_SECURE) { |
| // Kernel told us whether to enable secure mode. |
| _AT_SECURE_value = v[1]; |
| return; |
| } |
| } |
| |
| // We don't support ancient kernels. |
| const char* msg = "FATAL: kernel did not supply AT_SECURE\n"; |
| write(2, msg, strlen(msg)); |
| exit(EXIT_FAILURE); |
| } |
| |
| static void __remove_unsafe_environment_variables() { |
| // None of these should be allowed in setuid programs. |
| static const char* const UNSAFE_VARIABLE_NAMES[] = { |
| "GCONV_PATH", |
| "GETCONF_DIR", |
| "HOSTALIASES", |
| "LD_AOUT_LIBRARY_PATH", |
| "LD_AOUT_PRELOAD", |
| "LD_AUDIT", |
| "LD_DEBUG", |
| "LD_DEBUG_OUTPUT", |
| "LD_DYNAMIC_WEAK", |
| "LD_LIBRARY_PATH", |
| "LD_ORIGIN_PATH", |
| "LD_PRELOAD", |
| "LD_PROFILE", |
| "LD_SHOW_AUXV", |
| "LD_USE_LOAD_BIAS", |
| "LOCALDOMAIN", |
| "LOCPATH", |
| "MALLOC_CHECK_", |
| "MALLOC_TRACE", |
| "NIS_PATH", |
| "NLSPATH", |
| "RESOLV_HOST_CONF", |
| "RES_OPTIONS", |
| "TMPDIR", |
| "TZDIR", |
| NULL |
| }; |
| for (size_t i = 0; UNSAFE_VARIABLE_NAMES[i] != NULL; ++i) { |
| linker_env_unset(UNSAFE_VARIABLE_NAMES[i]); |
| } |
| } |
| |
| static void __remove_invalid_environment_variables() { |
| char** src = _envp; |
| char** dst = _envp; |
| for (; src[0] != NULL; ++src) { |
| if (!_is_valid_definition(src[0])) { |
| continue; |
| } |
| dst[0] = src[0]; |
| ++dst; |
| } |
| dst[0] = NULL; |
| } |
| |
| unsigned* linker_env_init(unsigned* environment_and_aux_vectors) { |
| // Store environment pointer - can't be NULL. |
| _envp = reinterpret_cast<char**>(environment_and_aux_vectors); |
| |
| // Skip over all environment variable definitions. |
| // The end of the environment block is marked by two NULL pointers. |
| unsigned* aux_vectors = environment_and_aux_vectors; |
| while (aux_vectors[0] != 0) { |
| ++aux_vectors; |
| } |
| ++aux_vectors; |
| |
| __remove_invalid_environment_variables(); |
| __init_AT_SECURE(aux_vectors); |
| |
| // Sanitize environment if we're loading a setuid program. |
| if (get_AT_SECURE()) { |
| __remove_unsafe_environment_variables(); |
| } |
| |
| return aux_vectors; |
| } |
| |
| /* Check if the environment variable definition at 'envstr' |
| * starts with '<name>=', and if so return the address of the |
| * first character after the equal sign. Otherwise return NULL. |
| */ |
| static char* env_match(char* envstr, const char* name) { |
| size_t i = 0; |
| |
| while (envstr[i] == name[i] && name[i] != '\0') { |
| ++i; |
| } |
| |
| if (name[i] == '\0' && envstr[i] == '=') { |
| return envstr + i + 1; |
| } |
| |
| return NULL; |
| } |
| |
| const char* linker_env_get(const char* name) { |
| if (name == NULL || name[0] == '\0') { |
| return NULL; |
| } |
| |
| for (char** p = _envp; p[0] != NULL; ++p) { |
| char* val = env_match(p[0], name); |
| if (val != NULL) { |
| if (val[0] == '\0') { |
| return NULL; // Return NULL for empty strings. |
| } |
| return val; |
| } |
| } |
| return NULL; |
| } |
| |
| void linker_env_unset(const char* name) { |
| char** readp = _envp; |
| char** writep = readp; |
| |
| if (name == NULL || name[0] == '\0') { |
| return; |
| } |
| |
| for ( ; readp[0] != NULL; readp++ ) { |
| if (env_match(readp[0], name)) { |
| continue; |
| } |
| writep[0] = readp[0]; |
| writep++; |
| } |
| /* end list with a NULL */ |
| writep[0] = NULL; |
| } |