2 * Copyright (C) 2008 The Android Open Source Project
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29 #include "libc_init_common.h"
40 #include <sys/personality.h>
44 #include <async_safe/log.h>
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"
54 extern "C" abort_msg_t** __abort_message_ptr;
55 extern "C" int __system_properties_init(void);
57 __LIBC_HIDDEN__ WriteProtected<libc_globals> __libc_globals;
59 // Not public, but well-known in the BSDs.
60 const char* __progname;
62 // Declared in <unistd.h>.
66 __attribute__((__naked__)) static void __libc_int0x80() {
67 __asm__ volatile("int $0x80; ret");
70 __LIBC_HIDDEN__ void* __libc_sysinfo = reinterpret_cast<void*>(__libc_int0x80);
72 __LIBC_HIDDEN__ void __libc_init_sysinfo(KernelArgumentBlock& args) {
73 __libc_sysinfo = reinterpret_cast<void*>(args.getauxval(AT_SYSINFO));
76 // TODO: lose this function and just access __libc_sysinfo directly.
77 __LIBC_HIDDEN__ extern "C" void* __kernel_syscall() {
78 return __libc_sysinfo;
82 void __libc_init_globals(KernelArgumentBlock& args) {
84 __libc_init_sysinfo(args);
86 // Initialize libc globals that are needed in both the linker and in libc.
87 // In dynamic binaries, this is run at least twice for different copies of the
88 // globals, once for the linker's copy and once for the one in libc.so.
89 __libc_auxv = args.auxv;
90 __libc_globals.initialize();
91 __libc_globals.mutate([&args](libc_globals* globals) {
92 __libc_init_vdso(globals, args);
93 __libc_init_setjmp_cookie(globals, args);
97 #if !defined(__LP64__)
98 static void __check_max_thread_id() {
99 if (gettid() > 65535) {
100 async_safe_fatal("Limited by the size of pthread_mutex_t, 32 bit bionic libc only accepts "
101 "pid <= 65535, but current pid is %d", gettid());
106 static void arc4random_fork_handler() {
111 void __libc_init_common(KernelArgumentBlock& args) {
112 // Initialize various globals.
115 __progname = args.argv[0] ? args.argv[0] : "<unknown>";
116 __abort_message_ptr = args.abort_message_ptr;
118 #if !defined(__LP64__)
119 __check_max_thread_id();
122 // Get the main thread from TLS and add it to the thread list.
123 pthread_internal_t* main_thread = __get_thread();
124 __pthread_internal_add(main_thread);
126 // Register atfork handlers to take and release the arc4random lock.
127 pthread_atfork(arc4random_fork_handler, _thread_arc4_unlock, _thread_arc4_unlock);
129 __system_properties_init(); // Requires 'environ'.
132 __noreturn static void __early_abort(int line) {
133 // We can't write to stdout or stderr because we're aborting before we've checked that
134 // it's safe for us to use those file descriptors. We probably can't strace either, so
135 // we rely on the fact that if we dereference a low address, either debuggerd or the
136 // kernel's crash dump will show the fault address.
137 *reinterpret_cast<int*>(line) = 0;
141 // Force any of the closed stdin, stdout and stderr to be associated with /dev/null.
142 static void __nullify_closed_stdio() {
143 int dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR));
144 if (dev_null == -1) {
145 // init won't have /dev/null available, but SELinux provides an equivalent.
146 dev_null = TEMP_FAILURE_RETRY(open("/sys/fs/selinux/null", O_RDWR));
148 if (dev_null == -1) {
149 __early_abort(__LINE__);
152 // If any of the stdio file descriptors is valid and not associated
153 // with /dev/null, dup /dev/null to it.
154 for (int i = 0; i < 3; i++) {
155 // If it is /dev/null already, we are done.
160 // Is this fd already open?
161 int status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL));
166 // The only error we allow is that the file descriptor does not
167 // exist, in which case we dup /dev/null to it.
168 if (errno == EBADF) {
169 // Try dupping /dev/null to this stdio file descriptor and
170 // repeat if there is a signal. Note that any errors in closing
171 // the stdio descriptor are lost.
172 status = TEMP_FAILURE_RETRY(dup2(dev_null, i));
174 __early_abort(__LINE__);
177 __early_abort(__LINE__);
181 // If /dev/null is not one of the stdio file descriptors, close it.
183 if (close(dev_null) == -1) {
184 __early_abort(__LINE__);
189 // Check if the environment variable definition at 'envstr'
190 // starts with '<name>=', and if so return the address of the
191 // first character after the equal sign. Otherwise return null.
192 static const char* env_match(const char* envstr, const char* name) {
195 while (envstr[i] == name[i] && name[i] != '\0') {
199 if (name[i] == '\0' && envstr[i] == '=') {
200 return envstr + i + 1;
206 static bool __is_valid_environment_variable(const char* name) {
207 // According to the kernel source, by default the kernel uses 32*PAGE_SIZE
208 // as the maximum size for an environment variable definition.
209 const int MAX_ENV_LEN = 32*4096;
211 if (name == nullptr) {
215 // Parse the string, looking for the first '=' there, and its size.
217 int first_equal_pos = -1;
218 while (pos < MAX_ENV_LEN) {
219 if (name[pos] == '\0') {
222 if (name[pos] == '=' && first_equal_pos < 0) {
223 first_equal_pos = pos;
228 // Check that it's smaller than MAX_ENV_LEN (to detect non-zero terminated strings).
229 if (pos >= MAX_ENV_LEN) {
233 // Check that it contains at least one equal sign that is not the first character
234 if (first_equal_pos < 1) {
241 static bool __is_unsafe_environment_variable(const char* name) {
242 // None of these should be allowed when the AT_SECURE auxv
243 // flag is set. This flag is set to inform userspace that a
244 // security transition has occurred, for example, as a result
245 // of executing a setuid program or the result of an SELinux
246 // security transition.
247 static constexpr const char* UNSAFE_VARIABLE_NAMES[] = {
253 "LD_AOUT_LIBRARY_PATH",
277 for (const auto& unsafe_variable_name : UNSAFE_VARIABLE_NAMES) {
278 if (env_match(name, unsafe_variable_name) != nullptr) {
285 static void __sanitize_environment_variables(char** env) {
286 bool is_AT_SECURE = getauxval(AT_SECURE);
289 for (; src[0] != nullptr; ++src) {
290 if (!__is_valid_environment_variable(src[0])) {
293 // Remove various unsafe environment variables if we're loading a setuid program.
294 if (is_AT_SECURE && __is_unsafe_environment_variable(src[0])) {
303 static void __initialize_personality() {
304 #if !defined(__LP64__)
305 int old_value = personality(0xffffffff);
306 if (old_value == -1) {
307 async_safe_fatal("error getting old personality value: %s", strerror(errno));
310 if (personality((static_cast<unsigned int>(old_value) & ~PER_MASK) | PER_LINUX32) == -1) {
311 async_safe_fatal("error setting PER_LINUX32 personality: %s", strerror(errno));
316 void __libc_init_AT_SECURE(KernelArgumentBlock& args) {
317 __libc_auxv = args.auxv;
318 __abort_message_ptr = args.abort_message_ptr;
320 // Check that the kernel provided a value for AT_SECURE.
321 bool found_AT_SECURE = false;
322 for (ElfW(auxv_t)* v = __libc_auxv; v->a_type != AT_NULL; ++v) {
323 if (v->a_type == AT_SECURE) {
324 found_AT_SECURE = true;
328 if (!found_AT_SECURE) __early_abort(__LINE__);
330 if (getauxval(AT_SECURE)) {
331 // If this is a setuid/setgid program, close the security hole described in
332 // https://www.freebsd.org/security/advisories/FreeBSD-SA-02:23.stdio.asc
333 __nullify_closed_stdio();
335 __sanitize_environment_variables(args.envp);
338 // Now the environment has been sanitized, make it available.
341 __initialize_personality();
344 /* This function will be called during normal program termination
345 * to run the destructors that are listed in the .fini_array section
346 * of the executable, if any.
348 * 'fini_array' points to a list of function addresses. The first
349 * entry in the list has value -1, the last one has value 0.
351 void __libc_fini(void* array) {
352 typedef void (*Dtor)();
353 Dtor* fini_array = reinterpret_cast<Dtor*>(array);
354 const Dtor minus1 = reinterpret_cast<Dtor>(static_cast<uintptr_t>(-1));
356 // Sanity check - first entry must be -1.
357 if (array == NULL || fini_array[0] != minus1) {
364 // Count the number of destructors.
366 while (fini_array[count] != NULL) {
370 // Now call each destructor in reverse order.
372 Dtor dtor = fini_array[--count];
374 // Sanity check, any -1 in the list is ignored.
375 if (dtor == minus1) {