// SPDX-License-Identifier: GPL-2.0-only

  #include <linux/export.h>

  #include <linux/sched/signal.h>

  #include <linux/sched/task.h>

  #include <linux/fs.h>
  #include <linux/path.h>
  #include <linux/slab.h>

  #include <linux/fs_struct.h>

  #include "internal.h"

  /*
   * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
   * It can block.
   */

  void set_fs_root(struct fs_struct *fs, const struct path *path)

  {
  	struct path old_root;

  	path_get(path);

  	spin_lock(&fs->lock);

  	write_seqcount_begin(&fs->seq);

  	old_root = fs->root;
  	fs->root = *path;

  	write_seqcount_end(&fs->seq);

  	spin_unlock(&fs->lock);

  	if (old_root.dentry)

  		path_put(&old_root);

  }
  
  /*
   * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
   * It can block.
   */

  void set_fs_pwd(struct fs_struct *fs, const struct path *path)

  {
  	struct path old_pwd;

  	path_get(path);

  	spin_lock(&fs->lock);

  	write_seqcount_begin(&fs->seq);

  	old_pwd = fs->pwd;
  	fs->pwd = *path;

  	write_seqcount_end(&fs->seq);

  	spin_unlock(&fs->lock);

  
  	if (old_pwd.dentry)

  		path_put(&old_pwd);

  }

  static inline int replace_path(struct path *p, const struct path *old, const struct path *new)
  {
  	if (likely(p->dentry != old->dentry || p->mnt != old->mnt))
  		return 0;
  	*p = *new;
  	return 1;
  }

  void chroot_fs_refs(const struct path *old_root, const struct path *new_root)

  {
  	struct task_struct *g, *p;
  	struct fs_struct *fs;
  	int count = 0;
  
  	read_lock(&tasklist_lock);
  	do_each_thread(g, p) {
  		task_lock(p);
  		fs = p->fs;
  		if (fs) {

  			int hits = 0;

  			spin_lock(&fs->lock);

  			write_seqcount_begin(&fs->seq);

  			hits += replace_path(&fs->root, old_root, new_root);
  			hits += replace_path(&fs->pwd, old_root, new_root);
  			write_seqcount_end(&fs->seq);
  			while (hits--) {

  				count++;

  				path_get(new_root);

  			}

  			spin_unlock(&fs->lock);

  		}
  		task_unlock(p);
  	} while_each_thread(g, p);
  	read_unlock(&tasklist_lock);
  	while (count--)

  		path_put(old_root);

  }

  void free_fs_struct(struct fs_struct *fs)

  {

  	path_put(&fs->root);
  	path_put(&fs->pwd);

  	kmem_cache_free(fs_cachep, fs);

  }
  
  void exit_fs(struct task_struct *tsk)
  {

  	struct fs_struct *fs = tsk->fs;

  
  	if (fs) {

  		int kill;

  		task_lock(tsk);

  		spin_lock(&fs->lock);

  		tsk->fs = NULL;

  		kill = !--fs->users;

  		spin_unlock(&fs->lock);

  		task_unlock(tsk);

  		if (kill)
  			free_fs_struct(fs);

  	}
  }
  
  struct fs_struct *copy_fs_struct(struct fs_struct *old)
  {
  	struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
  	/* We don't need to lock fs - think why ;-) */
  	if (fs) {

  		fs->users = 1;
  		fs->in_exec = 0;

  		spin_lock_init(&fs->lock);

  		seqcount_spinlock_init(&fs->seq, &fs->lock);

  		fs->umask = old->umask;

  
  		spin_lock(&old->lock);
  		fs->root = old->root;

  		path_get(&fs->root);

  		fs->pwd = old->pwd;

  		path_get(&fs->pwd);

  		spin_unlock(&old->lock);

  	}
  	return fs;
  }
  
  int unshare_fs_struct(void)
  {

  	struct fs_struct *fs = current->fs;
  	struct fs_struct *new_fs = copy_fs_struct(fs);
  	int kill;
  
  	if (!new_fs)

  		return -ENOMEM;

  
  	task_lock(current);

  	spin_lock(&fs->lock);

  	kill = !--fs->users;
  	current->fs = new_fs;

  	spin_unlock(&fs->lock);

  	task_unlock(current);
  
  	if (kill)
  		free_fs_struct(fs);

  	return 0;
  }
  EXPORT_SYMBOL_GPL(unshare_fs_struct);

  int current_umask(void)
  {
  	return current->fs->umask;
  }
  EXPORT_SYMBOL(current_umask);

  /* to be mentioned only in INIT_TASK */
  struct fs_struct init_fs = {

  	.users		= 1,

  	.lock		= __SPIN_LOCK_UNLOCKED(init_fs.lock),

  	.seq		= SEQCNT_SPINLOCK_ZERO(init_fs.seq, &init_fs.lock),

  	.umask		= 0022,
  };