bin/override.c

   1 /*****************************************************************************
   2  * override.c: overriden function calls for VLC media player
   3  *****************************************************************************
   4  * Copyright (C) 2010 Rémi Denis-Courmont
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  19  *****************************************************************************/
  20
  21 #ifdef HAVE_CONFIG_H
  22 # include "config.h"
  23 #endif
  24
  25 #include <stdbool.h>
  26 #define MAX_ERRORS 5
  27
  28 void vlc_enable_override (void);
  29
  30 #if defined (__GNUC__) /* typeof and statement-expression */ \
  31  && (defined (__ELF__) && !defined (__sun__))
  32 /* Solaris crashes on printf("%s", NULL); which is legal, but annoying. */
  33
  34 #include <stdarg.h>
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <dlfcn.h>
  38 #include <pthread.h>
  39 #ifdef HAVE_EXECINFO_H
  40 # include <execinfo.h>
  41 #endif
  42 #ifdef NDEBUG
  43 # undef HAVE_BACKTRACE
  44 #endif
  45
  46 static bool override = false;
  47
  48 static void vlc_reset_override (void)
  49 {
  50     override = false;
  51 }
  52
  53 void vlc_enable_override (void)
  54 {
  55     override = true;
  56     pthread_atfork (NULL, NULL, vlc_reset_override);
  57 }
  58
  59 static void vlogbug (unsigned *pc, const char *level, const char *func,
  60                      const char *fmt, va_list ap)
  61 {
  62 #ifdef HAVE_BACKTRACE
  63     const size_t framec = 5;
  64     void *framev[framec];
  65
  66     backtrace (framev, framec);
  67 #endif
  68     flockfile (stderr);
  69     if (*pc < MAX_ERRORS)
  70     {
  71         (*pc)++;
  72         fprintf (stderr, "%s: call to %s(", level, func);
  73         vfprintf (stderr, fmt, ap);
  74         fputs (")\n", stderr);
  75         fflush (stderr);
  76 #ifdef HAVE_BACKTRACE
  77         backtrace_symbols_fd (framev + 2, framec - 2, fileno (stderr));
  78 #endif
  79     }
  80     funlockfile (stderr);
  81 }
  82
  83 static void logbug (unsigned *pc, const char *level, const char *func,
  84                     const char *fmt, ...)
  85 {
  86     va_list ap;
  87
  88     va_start (ap, fmt);
  89     vlogbug (pc, level, func, fmt, ap);
  90     va_end (ap);
  91 }
  92
  93 static void *getsym (const char *name)
  94 {
  95     void *sym = dlsym (RTLD_NEXT, name);
  96     if (sym == NULL)
  97     {
  98         fprintf (stderr, "Cannot resolve symbol %s: %s\n", name,
  99                  dlerror ());
 100         abort ();
 101     }
 102     return sym;
 103 }
 104
 105 #define LOG(level, ...) \
 106     do { \
 107         static unsigned counter = 0; \
 108         logbug(&counter, level, __func__, __VA_ARGS__); \
 109     } while (0)
 110
 111 #define CALL(func, ...) \
 112     ({ typeof (func) *sym = getsym ( # func); sym (__VA_ARGS__); })
 113
 114
 115 /*** Environment ***
 116  *
 117  * "Conforming multi-threaded applications shall not use the environ variable
 118  *  to access or modify any environment variable while any other thread is
 119  *  concurrently modifying any environment variable." -- POSIX.
 120  *
 121  * Some evil libraries modify the environment. We currently ignore the calls as
 122  * they could crash the process. This may cause funny behaviour though. */
 123 int putenv (char *str)
 124 {
 125     if (override)
 126     {
 127         LOG("Blocked", "\"%s\"", str);
 128         return 0;
 129     }
 130     return CALL(putenv, str);
 131 }
 132
 133 int setenv (const char *name, const char *value, int overwrite)
 134 {
 135     if (override)
 136     {
 137         LOG("Blocked", "\"%s\", \"%s\", %d", name, value, overwrite);
 138         return 0;
 139     }
 140     return CALL(setenv, name, value, overwrite);
 141 }
 142
 143 int unsetenv (const char *name)
 144 {
 145     if (override)
 146     {
 147         LOG("Blocked", "\"%s\"", name);
 148         return 0;
 149     }
 150     return CALL(unsetenv, name);
 151 }
 152
 153
 154 /*** Pseudo random numbers ***
 155  *
 156  * The C PRNG is not thread-safe (and generally sucks, the POSIX 48-bits PRNG
 157  * is much better as a reproducible non-secure PRNG). To work around this, we
 158  * force evil callers to serialize. This makes the call safe, but fails to
 159  * preserve reproducibility of the number sequence (which usually does not
 160  * matter).
 161  **/
 162 static struct
 163 {
 164     pthread_mutex_t lock;
 165     unsigned int seed;
 166 } prng = { PTHREAD_MUTEX_INITIALIZER, 0, };
 167
 168 void srand (unsigned int seed)
 169 {
 170     pthread_mutex_lock (&prng.lock);
 171     LOG("Warning", "%d", seed);
 172     prng.seed = seed;
 173     pthread_mutex_unlock (&prng.lock);
 174 }
 175
 176 int rand (void)
 177 {
 178     int ret;
 179
 180     pthread_mutex_lock (&prng.lock);
 181     LOG("Warning", "");
 182     ret = rand_r (&prng.seed);
 183     pthread_mutex_unlock (&prng.lock);
 184     return ret;
 185 }
 186
 187
 188 /** Signals **/
 189 #include <signal.h>
 190
 191 static bool blocked_signal (int num)
 192 {
 193     switch (num)
 194     {
 195         case SIGINT:
 196         case SIGHUP:
 197         case SIGQUIT:
 198         case SIGTERM:
 199         case SIGPIPE:
 200         case SIGCHLD:
 201             return true;
 202     }
 203     return false;
 204 }
 205
 206 void (*signal (int signum, void (*handler) (int))) (int)
 207 {
 208     if (override)
 209     {
 210         if (handler != SIG_IGN && handler != SIG_DFL)
 211             goto error;
 212         if (!blocked_signal (signum))
 213             goto error;
 214         /* For our blocked signals, the handler won't matter much... */
 215         LOG("Warning", "%d, %p", signum, handler);
 216     }
 217     return CALL(signal, signum, handler);
 218 error:
 219     LOG("Blocked", "%d, %p", signum, handler);
 220     return SIG_DFL;
 221 }
 222
 223 int sigaction (int signum, const struct sigaction *act, struct sigaction *old)
 224 {
 225     if (override && act != NULL)
 226     {
 227         if ((act->sa_flags & SA_SIGINFO)
 228          || (act->sa_handler != SIG_IGN && act->sa_handler != SIG_DFL))
 229             goto error;
 230         LOG("Warning", "%d, %p, %p", signum, act, old);
 231     }
 232     return CALL(sigaction, signum, act, old);
 233 error:
 234     LOG("Blocked", "%d, %p, %p", signum, act, old);
 235     return -1;
 236 }
 237
 238
 239 /*** Locales ***
 240  * setlocale() is not thread-safe and has a tendency to crash other threads as
 241  * quite many libc and libintl calls depend on the locale.
 242  * Use uselocale() instead for thread-safety.
 243  */
 244 #include <locale.h>
 245
 246 char *setlocale (int cat, const char *locale)
 247 {
 248     if (override && locale != NULL)
 249     {
 250         LOG("Blocked", "%d, \"%s\"", cat, locale);
 251         return NULL;
 252     }
 253     return CALL(setlocale, cat, locale);
 254 }
 255
 256
 257 /*** Xlib ****/
 258 #ifdef HAVE_X11_XLIB_H
 259 # include <X11/Xlib.h>
 260
 261 static pthread_mutex_t xlib_lock = PTHREAD_MUTEX_INITIALIZER;
 262
 263 int (*XSetErrorHandler (int (*handler) (Display *, XErrorEvent *)))
 264      (Display *, XErrorEvent *)
 265 {
 266     if (override)
 267     {
 268         int (*ret) (Display *, XErrorEvent *);
 269
 270         pthread_mutex_lock (&xlib_lock);
 271         LOG("Error", "%p", handler);
 272         ret = CALL(XSetErrorHandler, handler);
 273         pthread_mutex_unlock (&xlib_lock);
 274         return ret;
 275     }
 276     return CALL(XSetErrorHandler, handler);
 277 }
 278
 279 int (*XSetIOErrorHandler (int (*handler) (Display *))) (Display *)
 280 {
 281     if (override)
 282     {
 283         int (*ret) (Display *);
 284
 285         pthread_mutex_lock (&xlib_lock);
 286         LOG("Error", "%p", handler);
 287         ret = CALL(XSetIOErrorHandler, handler);
 288         pthread_mutex_unlock (&xlib_lock);
 289         return ret;
 290     }
 291     return CALL(XSetIOErrorHandler, handler);
 292 }
 293 #endif
 294
 295 /*** Buggy shared objects ***/
 296 #include <string.h>
 297
 298 void *dlopen (const char *path, int flag)
 299 {
 300     if (path && strstr (path, "/gui_platform/libkde.so"))
 301         return NULL; /* Oh no, not that one! */
 302     return CALL(dlopen, path, flag);
 303 }
 304
 305 #else
 306 void vlc_enable_override (void)
 307 {
 308 }
 309 #endif