we are able to parse str to int in the kernel

scripts/yt-block/unkillable.c

@@ -0,0 +1,104 @@
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/proc_fs.h>
+#include <linux/sched.h>
+#include <linux/sched/signal.h>
+#include <linux/pid.h>
+
+/* device access functions */
+ssize_t unkillable_write(struct file *filp, const char *buf, size_t count, loff_t *f_pos);
+ssize_t unkillable_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
+int unkillable_open(struct inode *inode, struct file *filp);
+int unkillable_release(struct inode *inode, struct file *filp);
+
+void unkillable_exit(void);
+int unkillable_init(void);
+
+struct file_operations unkillable_fops = {
+  .read = unkillable_read,
+  .write = unkillable_write,
+  .open = unkillable_open,
+  .release = unkillable_release
+};
+
+int unkillable_major = 117;
+
+int unkillable_init(void) 
+{
+  if (register_chrdev(unkillable_major, "unkillable", &unkillable_fops) < 0 ) {
+    printk("Unkillable: cannot obtain major number %d\n", unkillable_major);
+    return 1;
+  }
+
+  printk("Inserting unkillable module\n"); 
+  return 0;
+}
+
+void unkillable_exit(void) 
+{
+  unregister_chrdev(unkillable_major, "unkillable");
+  printk("Removing unkillable module\n");
+}
+
+int unkillable_open(struct inode *inode, struct file *filp) 
+{
+  return 0;
+}
+
+int unkillable_release(struct inode *inode, struct file *filp) 
+{
+  return 0;
+}
+
+ssize_t unkillable_read(struct file *filp, char *buf, size_t count, loff_t *f_pos) 
+{ 
+  struct pid *pid_struct;
+  struct task_struct *p;
+  
+  /* interpret count to read as target pid */
+  printk("Unkillable: Got pid %d", (int) count);
+
+  /* get the pid struct */
+  pid_struct = find_get_pid((int) count);
+
+  /* get the task_struct from the pid */
+  p = pid_task(pid_struct, PIDTYPE_PID);
+
+  /* add the flag */
+  p->signal->flags = p->signal->flags | SIGNAL_UNKILLABLE;
+  printk("Unkillable: pid %d marked as unkillable\n", (int) count);
+  
+  if (*f_pos == 0) { 
+    *f_pos+=1; 
+    return 1; 
+  } else { 
+    return 0; 
+  }
+}
+
+ssize_t unkillable_write(struct file *filp, const char *buf, size_t count, loff_t *f_pos) 
+{
+  int ret;
+  unsigned long long res;
+
+  ret = kstrtoull_from_user(buf, count, 10, &res);
+
+  if (ret) {
+      /* Negative error code. */
+      pr_info("ko = %d\n", ret);
+      return ret;
+  } else {
+      pr_info("ok ... pid: %llu\n", res);
+      return count;
+  }
+}
+
+
+/* Declaration of the init and exit functions */
+module_init(unkillable_init);
+module_exit(unkillable_exit);
+
+MODULE_LICENSE("GPL");
+