ERROR: modpost: "kallsyms_on_each_symbol"

Question

I am trying to create a kernel module that changes the PID of a process. I searched in google and came across many articles that references this github

https://github.com/gravit0/changepid/blob/master/module/main.c

For the above github i took the following parts that should be responsible for the PID change.

static void* find_sym( const char *sym ) {  // find address kernel symbol sym 
   static unsigned long faddr = 0;          // static !!! 
   // ----------- nested functions are a GCC extension --------- 
   int symb_fn( void* data, const char* sym, struct module* mod, unsigned long addr ) { 
      if( 0 == strcmp( (char*)data, sym ) ) { 
         faddr = addr; 
         return 1; 
      } 
      else return 0; 
   }; 
   // -------------------------------------------------------- 
   kallsyms_on_each_symbol( symb_fn, (void*)sym ); 
   return (void*)faddr; 
}

static asmlinkage void (*change_pidR)(struct task_struct *task, enum pid_type type,
        struct pid *pid);
static asmlinkage struct pid* (*alloc_pidR)(struct pid_namespace *ns);

 change_pidR = find_sym("change_pid");
 alloc_pidR = find_sym("alloc_pid");

On compilation i get the following error on the kallsyms_on_each_symbol() function

MODPOST /home/anastasis/projects/Module.symvers
ERROR: modpost: "kallsyms_on_each_symbol" [home/anastasis/projects/change_pid.ko] undefined!

How do i fix this?

PS. As a potential fix i installed a new kernel on a vm and i made sure that the option about kallsyms is enabled, but i still get the same ERROR.

ERROR: modpost: "kallsyms_on_each_symbol"

0 Answers