Setting the AFL_I_AM_THE_FORKSERVER environment variable in the begining of the forkserver child process, and unsetting it when the target is launched

instrumentation/afl-compiler-rt.o.c

@@ -1046,6 +1046,7 @@ static void __afl_start_forkserver(void) {
       /* In child process: close fds, resume execution. */
 
       if (unlikely(!child_pid)) {  // just to signal afl-fuzz faster
+        unsetenv("AFL_I_AM_THE_FORKSERVER");
 
         //(void)nice(-20);
 

src/afl-forkserver.c

@@ -878,6 +878,8 @@ void afl_fsrv_start(afl_forkserver_t *fsrv, char **argv,
 
     /* CHILD PROCESS */
 
+    setenv("AFL_I_AM_THE_FORKSERVER", "1", 0);
+
     // enable terminating on sigpipe in the children
     struct sigaction sa;
     memset((char *)&sa, 0, sizeof(sa));