#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/syscalls.h>
#include <linux/unistd.h>
#include <linux/proc_fs.h>
#include <asm/uaccess.h>
#include <linux/namei.h>
#include <linux/fs.h>


int flag=0;

#define MAX_TRY 1024;

MODULE_LICENSE ("GPL");

unsigned long *sys_call_table;

asmlinkage long (*original_sys_open) (const char __user * filename, int
flags, int mode);

asmlinkage int our_fake_open_function(const char __user *filename, int
flags, int mode)
{
        int error;
        struct nameidata nd,nd_t;
        struct inode *inode,*inode_t;
        mm_segment_t fs;

        error=user_path_walk(filename,&nd);

        if(!error)
        {

                inode=nd.dentry->d_inode;

                /*Have to do this before calling user_path_walk( )
                from kernel space:*/
                fs=get_fs( );
                set_fs(get_ds( ));

                /*Protect /tmp/test. Change this to whatever file you
                want to protect*/
                error=user_path_walk("/tmp/test",&nd_t);

                set_fs(fs);

                if(!error)
                {
                        inode_t=nd_t.dentry->d_inode;

                        if(inode==inode_t)
                                return -EACCES;
                }
        }
  
        return original_sys_open(filename,flags,mode);
}
        
static int __init my_init (void)
{
        int i=MAX_TRY;
        unsigned long *sys_table;
        sys_table = (unsigned long *)&system_utsname;

        while(i)
        {
                if(sys_table[__NR_read] == (unsigned long)sys_read)
                {
                        sys_call_table=sys_table;
                        flag=1;
                        break;   
                }
                i--;
                sys_table++;
                
        }
                
        if(flag)
        {
            original_sys_open =(void * )xchg(&sys_call_table[__NR_open],
our_fake_open_function);
        }
                                
        return 0;

}
        
static void my_exit (void)
{
        xchg(&sys_call_table[__NR_open], original_sys_open);
}
        
module_init(my_init);
module_exit(my_exit);