libc_init_common.cpp revision 864f3ec1865c1185acf5ac1652b7b790abea76b0
1/* 2 * Copyright (C) 2008 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 29#include "libc_init_common.h" 30 31#include <elf.h> 32#include <errno.h> 33#include <fcntl.h> 34#include <stddef.h> 35#include <stdint.h> 36#include <stdio.h> 37#include <stdlib.h> 38#include <string.h> 39#include <sys/auxv.h> 40#include <sys/personality.h> 41#include <sys/time.h> 42#include <unistd.h> 43 44#include "private/KernelArgumentBlock.h" 45#include "private/WriteProtected.h" 46#include "private/bionic_auxv.h" 47#include "private/bionic_globals.h" 48#include "private/bionic_tls.h" 49#include "private/libc_logging.h" 50#include "private/thread_private.h" 51#include "pthread_internal.h" 52 53extern "C" abort_msg_t** __abort_message_ptr; 54extern "C" int __system_properties_init(void); 55 56__LIBC_HIDDEN__ WriteProtected<libc_globals> __libc_globals; 57 58// Not public, but well-known in the BSDs. 59const char* __progname; 60 61// Declared in <unistd.h>. 62char** environ; 63 64#if defined(__i386__) 65__LIBC_HIDDEN__ void* __libc_sysinfo = nullptr; 66 67__LIBC_HIDDEN__ void __libc_init_sysinfo(KernelArgumentBlock& args) { 68 __libc_sysinfo = reinterpret_cast<void*>(args.getauxval(AT_SYSINFO)); 69} 70 71// TODO: lose this function and just access __libc_sysinfo directly. 72__LIBC_HIDDEN__ extern "C" void* __kernel_syscall() { 73 return __libc_sysinfo; 74} 75#endif 76 77void __libc_init_globals(KernelArgumentBlock& args) { 78#if defined(__i386__) 79 __libc_init_sysinfo(args); 80#endif 81 // Initialize libc globals that are needed in both the linker and in libc. 82 // In dynamic binaries, this is run at least twice for different copies of the 83 // globals, once for the linker's copy and once for the one in libc.so. 84 __libc_auxv = args.auxv; 85 __libc_globals.initialize(); 86 __libc_globals.mutate([&args](libc_globals* globals) { 87 __libc_init_vdso(globals, args); 88 __libc_init_setjmp_cookie(globals, args); 89 }); 90} 91 92#if !defined(__LP64__) 93static void __check_max_thread_id() { 94 if (gettid() > 65535) { 95 __libc_fatal("Limited by the size of pthread_mutex_t, 32 bit bionic libc only accepts " 96 "pid <= 65535, but current pid is %d", gettid()); 97 } 98} 99#endif 100 101static void arc4random_fork_handler() { 102 _rs_forked = 1; 103 _thread_arc4_lock(); 104} 105 106void __libc_init_common(KernelArgumentBlock& args) { 107 // Initialize various globals. 108 environ = args.envp; 109 errno = 0; 110 __progname = args.argv[0] ? args.argv[0] : "<unknown>"; 111 __abort_message_ptr = args.abort_message_ptr; 112 113#if !defined(__LP64__) 114 __check_max_thread_id(); 115#endif 116 117 // Get the main thread from TLS and add it to the thread list. 118 pthread_internal_t* main_thread = __get_thread(); 119 __pthread_internal_add(main_thread); 120 121 // Register atfork handlers to take and release the arc4random lock. 122 pthread_atfork(arc4random_fork_handler, _thread_arc4_unlock, _thread_arc4_unlock); 123 124 __system_properties_init(); // Requires 'environ'. 125} 126 127__noreturn static void __early_abort(int line) { 128 // We can't write to stdout or stderr because we're aborting before we've checked that 129 // it's safe for us to use those file descriptors. We probably can't strace either, so 130 // we rely on the fact that if we dereference a low address, either debuggerd or the 131 // kernel's crash dump will show the fault address. 132 *reinterpret_cast<int*>(line) = 0; 133 _exit(EXIT_FAILURE); 134} 135 136// Force any of the closed stdin, stdout and stderr to be associated with /dev/null. 137static void __nullify_closed_stdio() { 138 int dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 139 if (dev_null == -1) { 140 // init won't have /dev/null available, but SELinux provides an equivalent. 141 dev_null = TEMP_FAILURE_RETRY(open("/sys/fs/selinux/null", O_RDWR)); 142 } 143 if (dev_null == -1) { 144 __early_abort(__LINE__); 145 } 146 147 // If any of the stdio file descriptors is valid and not associated 148 // with /dev/null, dup /dev/null to it. 149 for (int i = 0; i < 3; i++) { 150 // If it is /dev/null already, we are done. 151 if (i == dev_null) { 152 continue; 153 } 154 155 // Is this fd already open? 156 int status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 157 if (status != -1) { 158 continue; 159 } 160 161 // The only error we allow is that the file descriptor does not 162 // exist, in which case we dup /dev/null to it. 163 if (errno == EBADF) { 164 // Try dupping /dev/null to this stdio file descriptor and 165 // repeat if there is a signal. Note that any errors in closing 166 // the stdio descriptor are lost. 167 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 168 if (status == -1) { 169 __early_abort(__LINE__); 170 } 171 } else { 172 __early_abort(__LINE__); 173 } 174 } 175 176 // If /dev/null is not one of the stdio file descriptors, close it. 177 if (dev_null > 2) { 178 if (close(dev_null) == -1) { 179 __early_abort(__LINE__); 180 } 181 } 182} 183 184// Check if the environment variable definition at 'envstr' 185// starts with '<name>=', and if so return the address of the 186// first character after the equal sign. Otherwise return null. 187static const char* env_match(const char* envstr, const char* name) { 188 size_t i = 0; 189 190 while (envstr[i] == name[i] && name[i] != '\0') { 191 ++i; 192 } 193 194 if (name[i] == '\0' && envstr[i] == '=') { 195 return envstr + i + 1; 196 } 197 198 return nullptr; 199} 200 201static bool __is_valid_environment_variable(const char* name) { 202 // According to the kernel source, by default the kernel uses 32*PAGE_SIZE 203 // as the maximum size for an environment variable definition. 204 const int MAX_ENV_LEN = 32*4096; 205 206 if (name == nullptr) { 207 return false; 208 } 209 210 // Parse the string, looking for the first '=' there, and its size. 211 int pos = 0; 212 int first_equal_pos = -1; 213 while (pos < MAX_ENV_LEN) { 214 if (name[pos] == '\0') { 215 break; 216 } 217 if (name[pos] == '=' && first_equal_pos < 0) { 218 first_equal_pos = pos; 219 } 220 pos++; 221 } 222 223 // Check that it's smaller than MAX_ENV_LEN (to detect non-zero terminated strings). 224 if (pos >= MAX_ENV_LEN) { 225 return false; 226 } 227 228 // Check that it contains at least one equal sign that is not the first character 229 if (first_equal_pos < 1) { 230 return false; 231 } 232 233 return true; 234} 235 236static bool __is_unsafe_environment_variable(const char* name) { 237 // None of these should be allowed when the AT_SECURE auxv 238 // flag is set. This flag is set to inform userspace that a 239 // security transition has occurred, for example, as a result 240 // of executing a setuid program or the result of an SELinux 241 // security transition. 242 static constexpr const char* UNSAFE_VARIABLE_NAMES[] = { 243 "GCONV_PATH", 244 "GETCONF_DIR", 245 "HOSTALIASES", 246 "JE_MALLOC_CONF", 247 "LD_AOUT_LIBRARY_PATH", 248 "LD_AOUT_PRELOAD", 249 "LD_AUDIT", 250 "LD_DEBUG", 251 "LD_DEBUG_OUTPUT", 252 "LD_DYNAMIC_WEAK", 253 "LD_LIBRARY_PATH", 254 "LD_ORIGIN_PATH", 255 "LD_PRELOAD", 256 "LD_PROFILE", 257 "LD_SHOW_AUXV", 258 "LD_USE_LOAD_BIAS", 259 "LOCALDOMAIN", 260 "LOCPATH", 261 "MALLOC_CHECK_", 262 "MALLOC_CONF", 263 "MALLOC_TRACE", 264 "NIS_PATH", 265 "NLSPATH", 266 "RESOLV_HOST_CONF", 267 "RES_OPTIONS", 268 "TMPDIR", 269 "TZDIR", 270 }; 271 for (const auto& unsafe_variable_name : UNSAFE_VARIABLE_NAMES) { 272 if (env_match(name, unsafe_variable_name) != nullptr) { 273 return true; 274 } 275 } 276 return false; 277} 278 279static void __sanitize_environment_variables(char** env) { 280 bool is_AT_SECURE = getauxval(AT_SECURE); 281 char** src = env; 282 char** dst = env; 283 for (; src[0] != nullptr; ++src) { 284 if (!__is_valid_environment_variable(src[0])) { 285 continue; 286 } 287 // Remove various unsafe environment variables if we're loading a setuid program. 288 if (is_AT_SECURE && __is_unsafe_environment_variable(src[0])) { 289 continue; 290 } 291 dst[0] = src[0]; 292 ++dst; 293 } 294 dst[0] = nullptr; 295} 296 297static void __initialize_personality() { 298#if !defined(__LP64__) 299 int old_value = personality(0xffffffff); 300 if (old_value == -1) { 301 __libc_fatal("error getting old personality value: %s", strerror(errno)); 302 } 303 304 if (personality((static_cast<unsigned int>(old_value) & ~PER_MASK) | PER_LINUX32) == -1) { 305 __libc_fatal("error setting PER_LINUX32 personality: %s", strerror(errno)); 306 } 307#endif 308} 309 310void __libc_init_AT_SECURE(KernelArgumentBlock& args) { 311 __libc_auxv = args.auxv; 312 __abort_message_ptr = args.abort_message_ptr; 313 314 // Check that the kernel provided a value for AT_SECURE. 315 bool found_AT_SECURE = false; 316 for (ElfW(auxv_t)* v = __libc_auxv; v->a_type != AT_NULL; ++v) { 317 if (v->a_type == AT_SECURE) { 318 found_AT_SECURE = true; 319 break; 320 } 321 } 322 if (!found_AT_SECURE) __early_abort(__LINE__); 323 324 if (getauxval(AT_SECURE)) { 325 // If this is a setuid/setgid program, close the security hole described in 326 // https://www.freebsd.org/security/advisories/FreeBSD-SA-02:23.stdio.asc 327 __nullify_closed_stdio(); 328 329 __sanitize_environment_variables(args.envp); 330 } 331 332 // Now the environment has been sanitized, make it available. 333 environ = args.envp; 334 335 __initialize_personality(); 336} 337 338/* This function will be called during normal program termination 339 * to run the destructors that are listed in the .fini_array section 340 * of the executable, if any. 341 * 342 * 'fini_array' points to a list of function addresses. The first 343 * entry in the list has value -1, the last one has value 0. 344 */ 345void __libc_fini(void* array) { 346 typedef void (*Dtor)(); 347 Dtor* fini_array = reinterpret_cast<Dtor*>(array); 348 const Dtor minus1 = reinterpret_cast<Dtor>(static_cast<uintptr_t>(-1)); 349 350 // Sanity check - first entry must be -1. 351 if (array == NULL || fini_array[0] != minus1) { 352 return; 353 } 354 355 // Skip over it. 356 fini_array += 1; 357 358 // Count the number of destructors. 359 int count = 0; 360 while (fini_array[count] != NULL) { 361 ++count; 362 } 363 364 // Now call each destructor in reverse order. 365 while (count > 0) { 366 Dtor dtor = fini_array[--count]; 367 368 // Sanity check, any -1 in the list is ignored. 369 if (dtor == minus1) { 370 continue; 371 } 372 373 dtor(); 374 } 375} 376