cmdutils: remove the current working directory from the DLL search path on win32

Reviewed-by: Matt Oliver <protogonoi@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 3bf142c773)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

cmdutils.c

@@ -107,6 +107,15 @@ static void log_callback_report(void *ptr, int level, const char *fmt, va_list v
     }
 }
 
+void init_dynload(void)
+{
+#ifdef _WIN32
+    /* Calling SetDllDirectory with the empty string (but not NULL) removes the
+     * current working directory from the DLL search path as a security pre-caution. */
+    SetDllDirectory("");
+#endif
+}
+
 static void (*program_exit)(int ret);
 
 void register_exit(void (*cb)(int ret))

cmdutils.h

@@ -61,6 +61,11 @@ void register_exit(void (*cb)(int ret));
  */
 void exit_program(int ret) av_noreturn;
 
+/**
+ * Initialize dynamic library loading
+ */
+void init_dynload(void);
+
 /**
  * Initialize the cmdutils option system, in particular
  * allocate the *_opts contexts.

ffmpeg.c

@@ -4303,6 +4303,8 @@ int main(int argc, char **argv)
     int ret;
     int64_t ti;
 
+    init_dynload();
+
     register_exit(ffmpeg_cleanup);
 
     setvbuf(stderr,NULL,_IONBF,0); /* win32 runtime needs this */

ffplay.c

@@ -3776,6 +3776,8 @@ int main(int argc, char **argv)
     char dummy_videodriver[] = "SDL_VIDEODRIVER=dummy";
     char alsa_bufsize[] = "SDL_AUDIO_ALSA_SET_BUFFER_SIZE=1";
 
+    init_dynload();
+
     av_log_set_flags(AV_LOG_SKIP_REPEATED);
     parse_loglevel(argc, argv, options);
 

ffprobe.c

@@ -3241,6 +3241,8 @@ int main(int argc, char **argv)
     char *w_name = NULL, *w_args = NULL;
     int ret, i;
 
+    init_dynload();
+
     av_log_set_flags(AV_LOG_SKIP_REPEATED);
     register_exit(ffprobe_cleanup);
 

ffserver.c

@@ -3980,6 +3980,7 @@ int main(int argc, char **argv)
     int cfg_parsed;
     int ret = EXIT_FAILURE;
 
+    init_dynload();
 
     config.filename = av_strdup("/etc/ffserver.conf");