/*Check Stack - by Breno_BSD
    This kernel thread will verify the stack area of almost all tasks
    and try to safe your system of stack overflow ( just when the size of
    of stack is almost the same STK_LIM)
*/

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/unistd.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/string.h>
#include <asm/uaccess.h>
#include <asm/errno.h>
#include <asm/mman.h>
#include <asm/page.h>
#include <asm/pgalloc.h>
#include <asm/processor.h>
#include <asm-i386/vm86.h>

#define THREAD 1
#define STACK_LIMIT 8192
 
int check_stack()
{ 
struct task_struct *p = NULL;
struct vm_area_struct *vma;
unsigned long stack_size, stack_addr, stack_ptr;
    
    daemonize();
    sprintf(current->comm,"CHECK_STACK");
 
    for(;;schedule()) 
    {
	for_each_task(p)  /*Lets get all process*/
	{
	    if((p->mm != NULL) && (p->pid != 1)) 
	    {
		stack_addr = p->mm->start_stack;
		
		stack_ptr = p->thread.esp;
	
		vma = find_vma(p->mm,stack_addr);  /*find stack vma*/
		
		if(!vma)
		return 0;
		
		stack_size = (vma->vm_end - vma->vm_start)/PAGE_SIZE; /*Check the size*/
		
		if(stack_size >= (STACK_LIMIT - 1024))
		{
		    if(stack_size >= (STACK_LIMIT -  100)) /*Oops , this is not very good */
		    {
			printk(KERN_CRIT"Process not safe\n");
			force_sig(SIGKILL,p);
			return 0;
		    }
		
		
		    printk(KERN_CRIT"Process %s pid: %d\n",p->comm,p->pid);
		    printk(KERN_CRIT"Stack size %lu k\n",stack_size);
		    printk(KERN_CRIT"Start start addr %lu\n",stack_addr);
		    printk(KERN_CRIT"Stack pointer %lu\n",stack_ptr);
		    
		    vma->vm_flags &= ~(VM_WRITE | VM_READ); /*The stack is big enough*/
		    
		    return 0;
		 }
	    
	    }
	}
    } 			    	
 
 return 0;
}
 

int init_module()
{
int th_pid[THREAD];
int i;

    for(i = 0;i < THREAD;i++)
    th_pid[i] = kernel_thread(check_stack,NULL,CLONE_SIGHAND);

	if(th_pid[i] < 0)
	printk(KERN_CRIT"Cannot create thread\n");

return 0;
}

void cleanup_module()
{
}