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 <async_safe/log.h> 45 46 #include "private/KernelArgumentBlock.h" 47 #include "private/WriteProtected.h" 48 #include "private/bionic_auxv.h" 49 #include "private/bionic_globals.h" 50 #include "private/bionic_tls.h" 51 #include "private/thread_private.h" 52 #include "pthread_internal.h" 53 54 extern "C" abort_msg_t** __abort_message_ptr; 55 extern "C" int __system_properties_init(void); 56 57 __LIBC_HIDDEN__ WriteProtected<libc_globals> __libc_globals; 58 59 // Not public, but well-known in the BSDs. 60 const char* __progname; 61 62 #if defined(__i386__) 63 __attribute__((__naked__)) static void __libc_int0x80() { 64 __asm__ volatile("int $0x80; ret"); 65 } 66 67 __LIBC_HIDDEN__ void* __libc_sysinfo = reinterpret_cast<void*>(__libc_int0x80); 68 69 __LIBC_HIDDEN__ void __libc_init_sysinfo(KernelArgumentBlock& args) { 70 // Running under valgrind, AT_SYSINFO won't be set. 71 void* at_sysinfo = reinterpret_cast<void*>(args.getauxval(AT_SYSINFO)); 72 if (at_sysinfo != nullptr) __libc_sysinfo = at_sysinfo; 73 } 74 75 // TODO: lose this function and just access __libc_sysinfo directly. 76 __LIBC_HIDDEN__ extern "C" void* __kernel_syscall() { 77 return __libc_sysinfo; 78 } 79 #endif 80 81 void __libc_init_globals(KernelArgumentBlock& args) { 82 #if defined(__i386__) 83 __libc_init_sysinfo(args); 84 #endif 85 // Initialize libc globals that are needed in both the linker and in libc. 86 // In dynamic binaries, this is run at least twice for different copies of the 87 // globals, once for the linker's copy and once for the one in libc.so. 88 __libc_auxv = args.auxv; 89 __libc_globals.initialize(); 90 __libc_globals.mutate([&args](libc_globals* globals) { 91 __libc_init_vdso(globals, args); 92 __libc_init_setjmp_cookie(globals, args); 93 }); 94 } 95 96 #if !defined(__LP64__) 97 static void __check_max_thread_id() { 98 if (gettid() > 65535) { 99 async_safe_fatal("Limited by the size of pthread_mutex_t, 32 bit bionic libc only accepts " 100 "pid <= 65535, but current pid is %d", gettid()); 101 } 102 } 103 #endif 104 105 static void arc4random_fork_handler() { 106 _rs_forked = 1; 107 _thread_arc4_lock(); 108 } 109 110 void __libc_init_common(KernelArgumentBlock& args) { 111 // Initialize various globals. 112 environ = args.envp; 113 errno = 0; 114 __progname = args.argv[0] ? args.argv[0] : "<unknown>"; 115 __abort_message_ptr = args.abort_message_ptr; 116 117 #if !defined(__LP64__) 118 __check_max_thread_id(); 119 #endif 120 121 // Get the main thread from TLS and add it to the thread list. 122 pthread_internal_t* main_thread = __get_thread(); 123 __pthread_internal_add(main_thread); 124 125 // Register atfork handlers to take and release the arc4random lock. 126 pthread_atfork(arc4random_fork_handler, _thread_arc4_unlock, _thread_arc4_unlock); 127 128 __system_properties_init(); // Requires 'environ'. 129 } 130 131 __noreturn static void __early_abort(int line) { 132 // We can't write to stdout or stderr because we're aborting before we've checked that 133 // it's safe for us to use those file descriptors. We probably can't strace either, so 134 // we rely on the fact that if we dereference a low address, either debuggerd or the 135 // kernel's crash dump will show the fault address. 136 *reinterpret_cast<int*>(line) = 0; 137 _exit(EXIT_FAILURE); 138 } 139 140 // Force any of the closed stdin, stdout and stderr to be associated with /dev/null. 141 static void __nullify_closed_stdio() { 142 int dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); 143 if (dev_null == -1) { 144 // init won't have /dev/null available, but SELinux provides an equivalent. 145 dev_null = TEMP_FAILURE_RETRY(open("/sys/fs/selinux/null", O_RDWR)); 146 } 147 if (dev_null == -1) { 148 __early_abort(__LINE__); 149 } 150 151 // If any of the stdio file descriptors is valid and not associated 152 // with /dev/null, dup /dev/null to it. 153 for (int i = 0; i < 3; i++) { 154 // If it is /dev/null already, we are done. 155 if (i == dev_null) { 156 continue; 157 } 158 159 // Is this fd already open? 160 int status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); 161 if (status != -1) { 162 continue; 163 } 164 165 // The only error we allow is that the file descriptor does not 166 // exist, in which case we dup /dev/null to it. 167 if (errno == EBADF) { 168 // Try dupping /dev/null to this stdio file descriptor and 169 // repeat if there is a signal. Note that any errors in closing 170 // the stdio descriptor are lost. 171 status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); 172 if (status == -1) { 173 __early_abort(__LINE__); 174 } 175 } else { 176 __early_abort(__LINE__); 177 } 178 } 179 180 // If /dev/null is not one of the stdio file descriptors, close it. 181 if (dev_null > 2) { 182 if (close(dev_null) == -1) { 183 __early_abort(__LINE__); 184 } 185 } 186 } 187 188 // Check if the environment variable definition at 'envstr' 189 // starts with '<name>=', and if so return the address of the 190 // first character after the equal sign. Otherwise return null. 191 static const char* env_match(const char* envstr, const char* name) { 192 size_t i = 0; 193 194 while (envstr[i] == name[i] && name[i] != '\0') { 195 ++i; 196 } 197 198 if (name[i] == '\0' && envstr[i] == '=') { 199 return envstr + i + 1; 200 } 201 202 return nullptr; 203 } 204 205 static bool __is_valid_environment_variable(const char* name) { 206 // According to the kernel source, by default the kernel uses 32*PAGE_SIZE 207 // as the maximum size for an environment variable definition. 208 const int MAX_ENV_LEN = 32*4096; 209 210 if (name == nullptr) { 211 return false; 212 } 213 214 // Parse the string, looking for the first '=' there, and its size. 215 int pos = 0; 216 int first_equal_pos = -1; 217 while (pos < MAX_ENV_LEN) { 218 if (name[pos] == '\0') { 219 break; 220 } 221 if (name[pos] == '=' && first_equal_pos < 0) { 222 first_equal_pos = pos; 223 } 224 pos++; 225 } 226 227 // Check that it's smaller than MAX_ENV_LEN (to detect non-zero terminated strings). 228 if (pos >= MAX_ENV_LEN) { 229 return false; 230 } 231 232 // Check that it contains at least one equal sign that is not the first character 233 if (first_equal_pos < 1) { 234 return false; 235 } 236 237 return true; 238 } 239 240 static bool __is_unsafe_environment_variable(const char* name) { 241 // None of these should be allowed when the AT_SECURE auxv 242 // flag is set. This flag is set to inform userspace that a 243 // security transition has occurred, for example, as a result 244 // of executing a setuid program or the result of an SELinux 245 // security transition. 246 static constexpr const char* UNSAFE_VARIABLE_NAMES[] = { 247 "ANDROID_DNS_MODE", 248 "GCONV_PATH", 249 "GETCONF_DIR", 250 "HOSTALIASES", 251 "JE_MALLOC_CONF", 252 "LD_AOUT_LIBRARY_PATH", 253 "LD_AOUT_PRELOAD", 254 "LD_AUDIT", 255 "LD_DEBUG", 256 "LD_DEBUG_OUTPUT", 257 "LD_DYNAMIC_WEAK", 258 "LD_LIBRARY_PATH", 259 "LD_ORIGIN_PATH", 260 "LD_PRELOAD", 261 "LD_PROFILE", 262 "LD_SHOW_AUXV", 263 "LD_USE_LOAD_BIAS", 264 "LOCALDOMAIN", 265 "LOCPATH", 266 "MALLOC_CHECK_", 267 "MALLOC_CONF", 268 "MALLOC_TRACE", 269 "NIS_PATH", 270 "NLSPATH", 271 "RESOLV_HOST_CONF", 272 "RES_OPTIONS", 273 "TMPDIR", 274 "TZDIR", 275 }; 276 for (const auto& unsafe_variable_name : UNSAFE_VARIABLE_NAMES) { 277 if (env_match(name, unsafe_variable_name) != nullptr) { 278 return true; 279 } 280 } 281 return false; 282 } 283 284 static void __sanitize_environment_variables(char** env) { 285 bool is_AT_SECURE = getauxval(AT_SECURE); 286 char** src = env; 287 char** dst = env; 288 for (; src[0] != nullptr; ++src) { 289 if (!__is_valid_environment_variable(src[0])) { 290 continue; 291 } 292 // Remove various unsafe environment variables if we're loading a setuid program. 293 if (is_AT_SECURE && __is_unsafe_environment_variable(src[0])) { 294 continue; 295 } 296 dst[0] = src[0]; 297 ++dst; 298 } 299 dst[0] = nullptr; 300 } 301 302 static void __initialize_personality() { 303 #if !defined(__LP64__) 304 int old_value = personality(0xffffffff); 305 if (old_value == -1) { 306 async_safe_fatal("error getting old personality value: %s", strerror(errno)); 307 } 308 309 if (personality((static_cast<unsigned int>(old_value) & ~PER_MASK) | PER_LINUX32) == -1) { 310 async_safe_fatal("error setting PER_LINUX32 personality: %s", strerror(errno)); 311 } 312 #endif 313 } 314 315 void __libc_init_AT_SECURE(KernelArgumentBlock& args) { 316 __libc_auxv = args.auxv; 317 __abort_message_ptr = args.abort_message_ptr; 318 319 // Check that the kernel provided a value for AT_SECURE. 320 bool found_AT_SECURE = false; 321 for (ElfW(auxv_t)* v = __libc_auxv; v->a_type != AT_NULL; ++v) { 322 if (v->a_type == AT_SECURE) { 323 found_AT_SECURE = true; 324 break; 325 } 326 } 327 if (!found_AT_SECURE) __early_abort(__LINE__); 328 329 if (getauxval(AT_SECURE)) { 330 // If this is a setuid/setgid program, close the security hole described in 331 // https://www.freebsd.org/security/advisories/FreeBSD-SA-02:23.stdio.asc 332 __nullify_closed_stdio(); 333 334 __sanitize_environment_variables(args.envp); 335 } 336 337 // Now the environment has been sanitized, make it available. 338 environ = args.envp; 339 340 __initialize_personality(); 341 } 342 343 /* This function will be called during normal program termination 344 * to run the destructors that are listed in the .fini_array section 345 * of the executable, if any. 346 * 347 * 'fini_array' points to a list of function addresses. The first 348 * entry in the list has value -1, the last one has value 0. 349 */ 350 void __libc_fini(void* array) { 351 typedef void (*Dtor)(); 352 Dtor* fini_array = reinterpret_cast<Dtor*>(array); 353 const Dtor minus1 = reinterpret_cast<Dtor>(static_cast<uintptr_t>(-1)); 354 355 // Sanity check - first entry must be -1. 356 if (array == NULL || fini_array[0] != minus1) { 357 return; 358 } 359 360 // Skip over it. 361 fini_array += 1; 362 363 // Count the number of destructors. 364 int count = 0; 365 while (fini_array[count] != NULL) { 366 ++count; 367 } 368 369 // Now call each destructor in reverse order. 370 while (count > 0) { 371 Dtor dtor = fini_array[--count]; 372 373 // Sanity check, any -1 in the list is ignored. 374 if (dtor == minus1) { 375 continue; 376 } 377 378 dtor(); 379 } 380 } 381
