Safety checks for X11 error handlers

[vlc] / bin / override.c

diff --git a/bin/override.c b/bin/override.c
index 048c8fe1ca50d5f810951b228f26db19485521d0..113a63844597d4f61151616d6e9ab350bdf9972d 100644 (file)
--- a/bin/override.c
+++ b/bin/override.c
@@ -26,13 +26,6 @@
 
 void vlc_enable_override (void);
 
-static bool override = false;
-
-void vlc_enable_override (void)
-{
-    override = true;
-}
-
 #if defined (__GNUC__) /* typeof and statement-expression */ \
  && (defined (__ELF__) && !defined (__sun__))
 /* Solaris crashes on printf("%s", NULL); which is legal, but annoying. */
@@ -41,14 +34,41 @@ void vlc_enable_override (void)
 #include <stdio.h>
 #include <stdlib.h>
 #include <dlfcn.h>
+#include <pthread.h>
+#ifdef HAVE_EXECINFO_H
+# include <execinfo.h>
+#endif
+
+static bool override = false;
+
+static void vlc_reset_override (void)
+{
+    override = false;
+}
+
+void vlc_enable_override (void)
+{
+    override = true;
+    pthread_atfork (NULL, NULL, vlc_reset_override);
+}
 
 static void vlogbug (const char *level, const char *func, const char *fmt,
                      va_list ap)
 {
+#ifdef HAVE_BACKTRACE
+    const size_t framec = 8;
+    void *framev[framec];
+
+    backtrace (framev, framec);
+#endif
     flockfile (stderr);
     fprintf (stderr, "%s: call to %s(", level, func);
     vfprintf (stderr, fmt, ap);
     fputs (")\n", stderr);
+    fflush (stderr);
+#ifdef HAVE_BACKTRACE
+    backtrace_symbols_fd (framev + 2, framec - 2, fileno (stderr));
+#endif
     funlockfile (stderr);
 }
 
@@ -77,4 +97,140 @@ static void *getsym (const char *name)
     ({ typeof (func) *sym = getsym ( # func); sym (__VA_ARGS__); })
 
 
-#endif /* __ELF__ */
+/*** Environment ***
+ *
+ * "Conforming multi-threaded applications shall not use the environ variable
+ *  to access or modify any environment variable while any other thread is
+ *  concurrently modifying any environment variable." -- POSIX.
+ *
+ * Some evil libraries modify the environment. We currently ignore the calls as
+ * they could crash the process. This may cause funny behaviour though. */
+int putenv (char *str)
+{
+    if (override)
+    {
+        LOG("Blocked", "\"%s\"", str);
+        return 0;
+    }
+    return CALL(putenv, str);
+}
+
+int setenv (const char *name, const char *value, int overwrite)
+{
+    if (override)
+    {
+        LOG("Blocked", "\"%s\", \"%s\", %d", name, value, overwrite);
+        return 0;
+    }
+    return CALL(setenv, name, value, overwrite);
+}
+
+int unsetenv (const char *name)
+{
+    if (override)
+    {
+        LOG("Blocked", "\"%s\"", name);
+        return 0;
+    }
+    return CALL(unsetenv, name);
+}
+
+
+/*** Pseudo random numbers ***
+ *
+ * The C PRNG is not thread-safe (and generally sucks, the POSIX 48-bits PRNG
+ * is much better as a reproducible non-secure PRNG). To work around this, we
+ * force evil callers to serialize. This makes the call safe, but fails to
+ * preserve reproducibility of the number sequence (which usually does not
+ * matter).
+ **/
+static pthread_mutex_t prng_lock = PTHREAD_MUTEX_INITIALIZER;
+
+void srand (unsigned int seed)
+{
+    pthread_mutex_lock (&prng_lock);
+    LOG("Warning", "%d", seed);
+    CALL(srand, seed);
+    pthread_mutex_unlock (&prng_lock);
+}
+
+int rand (void)
+{
+    int ret;
+
+    pthread_mutex_lock (&prng_lock);
+    LOG("Warning", "");
+    ret = CALL(rand);
+    pthread_mutex_unlock (&prng_lock);
+    return ret;
+}
+
+
+/** Signals **/
+#include <signal.h>
+
+void (*signal (int signum, void (*handler) (int))) (int)
+{
+    if (override)
+    {
+        const char *msg = "Error";
+
+        if ((signum == SIGPIPE && handler == SIG_IGN)
+         || (signum != SIGPIPE && handler == SIG_DFL))
+            /* Same settings we already use */
+            msg = "Warning";
+        LOG(msg, "%d, %p", signum, handler);
+    }
+    return CALL(signal, signum, handler);
+}
+
+int sigaction (int signum, const struct sigaction *act, struct sigaction *old)
+{
+    if (act != NULL)
+        LOG("Error", "%d, %p, %p", signum, act, old);
+    return CALL(sigaction, signum, act, old);
+}
+
+
+/*** Xlib ****/
+#ifdef HAVE_X11_XLIB_H
+# include <X11/Xlib.h>
+
+static pthread_mutex_t xlib_lock = PTHREAD_MUTEX_INITIALIZER;
+
+int (*XSetErrorHandler (int (*handler) (Display *, XErrorEvent *)))
+     (Display *, XErrorEvent *)
+{
+    if (override)
+    {
+        int (*ret) (Display *, XErrorEvent *);
+
+        pthread_mutex_lock (&xlib_lock);
+        LOG("Error", "%p", handler);
+        ret = CALL(XSetErrorHandler, handler);
+        pthread_mutex_unlock (&xlib_lock);
+        return ret;
+    }
+    return CALL(XSetErrorHandler, handler);
+}
+
+int (*XSetIOErrorHandler (int (*handler) (Display *))) (Display *)
+{
+    if (override)
+    {
+        int (*ret) (Display *);
+
+        pthread_mutex_lock (&xlib_lock);
+        LOG("Error", "%p", handler);
+        ret = CALL(XSetIOErrorHandler, handler);
+        pthread_mutex_unlock (&xlib_lock);
+        return ret;
+    }
+    return CALL(XSetIOErrorHandler, handler);
+}
+#endif
+#else
+static void vlc_enable_override (void)
+{
+}
+#endif