// SPDX-License-Identifier: GPL-2.0

  /*
   *  linux/fs/readdir.c
   *
   *  Copyright (C) 1995  Linus Torvalds
   */

  #include <linux/stddef.h>

  #include <linux/kernel.h>

  #include <linux/export.h>

  #include <linux/time.h>
  #include <linux/mm.h>
  #include <linux/errno.h>
  #include <linux/stat.h>
  #include <linux/file.h>

  #include <linux/fs.h>

  #include <linux/fsnotify.h>

  #include <linux/dirent.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>
  #include <linux/unistd.h>

  #include <linux/compat.h>

  #include <linux/uaccess.h>

  #include <asm/unaligned.h>
  
  /*
   * Note the "unsafe_put_user() semantics: we goto a
   * label for errors.

   */
  #define unsafe_copy_dirent_name(_dst, _src, _len, label) do {	\
  	char __user *dst = (_dst);				\
  	const char *src = (_src);				\
  	size_t len = (_len);					\

  	unsafe_put_user(0, dst+len, label);			\
  	unsafe_copy_to_user(dst, src, len, label);		\

  } while (0)

  int iterate_dir(struct file *file, struct dir_context *ctx)

  {

  	struct inode *inode = file_inode(file);

  	bool shared = false;

  	int res = -ENOTDIR;

  	if (file->f_op->iterate_shared)
  		shared = true;
  	else if (!file->f_op->iterate)

  		goto out;
  
  	res = security_file_permission(file, MAY_READ);
  	if (res)
  		goto out;

  	if (shared)
  		res = down_read_killable(&inode->i_rwsem);
  	else

  		res = down_write_killable(&inode->i_rwsem);

  	if (res)
  		goto out;

  	res = -ENOENT;
  	if (!IS_DEADDIR(inode)) {

  		ctx->pos = file->f_pos;

  		if (shared)
  			res = file->f_op->iterate_shared(file, ctx);
  		else
  			res = file->f_op->iterate(file, ctx);

  		file->f_pos = ctx->pos;

  		fsnotify_access(file);

  		file_accessed(file);
  	}

  	if (shared)
  		inode_unlock_shared(inode);
  	else
  		inode_unlock(inode);

  out:
  	return res;
  }

  EXPORT_SYMBOL(iterate_dir);

  
  /*

   * POSIX says that a dirent name cannot contain NULL or a '/'.
   *
   * It's not 100% clear what we should really do in this case.
   * The filesystem is clearly corrupted, but returning a hard
   * error means that you now don't see any of the other names
   * either, so that isn't a perfect alternative.
   *
   * And if you return an error, what error do you use? Several
   * filesystems seem to have decided on EUCLEAN being the error
   * code for EFSCORRUPTED, and that may be the error to use. Or
   * just EIO, which is perhaps more obvious to users.
   *
   * In order to see the other file names in the directory, the
   * caller might want to make this a "soft" error: skip the
   * entry, and return the error at the end instead.
   *
   * Note that this should likely do a "memchr(name, 0, len)"
   * check too, since that would be filesystem corruption as
   * well. However, that case can't actually confuse user space,
   * which has to do a strlen() on the name anyway to find the
   * filename length, and the above "soft error" worry means
   * that it's probably better left alone until we have that
   * issue clarified.

   *
   * Note the PATH_MAX check - it's arbitrary but the real
   * kernel limit on a possible path component, not NAME_MAX,
   * which is the technical standard limit.

   */
  static int verify_dirent_name(const char *name, int len)
  {

  	if (len <= 0 || len >= PATH_MAX)

  		return -EIO;

  	if (memchr(name, '/', len))

  		return -EIO;
  	return 0;
  }
  
  /*

   * Traditional linux readdir() handling..
   *
   * "count=1" is a special case, meaning that the buffer is one
   * dirent-structure in size and that the code can't handle more
   * anyway. Thus the special "fillonedir()" function for that
   * case (the low-level handlers don't need to care about this).
   */

  
  #ifdef __ARCH_WANT_OLD_READDIR
  
  struct old_linux_dirent {
  	unsigned long	d_ino;
  	unsigned long	d_offset;
  	unsigned short	d_namlen;
  	char		d_name[1];
  };
  
  struct readdir_callback {

  	struct dir_context ctx;

  	struct old_linux_dirent __user * dirent;
  	int result;
  };

  static int fillonedir(struct dir_context *ctx, const char *name, int namlen,
  		      loff_t offset, u64 ino, unsigned int d_type)

  {

  	struct readdir_callback *buf =
  		container_of(ctx, struct readdir_callback, ctx);

  	struct old_linux_dirent __user * dirent;

  	unsigned long d_ino;

  
  	if (buf->result)
  		return -EINVAL;

  	d_ino = ino;

  	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
  		buf->result = -EOVERFLOW;

  		return -EOVERFLOW;

  	}

  	buf->result++;
  	dirent = buf->dirent;

  	if (!access_ok(dirent,

  			(unsigned long)(dirent->d_name + namlen + 1) -
  				(unsigned long)dirent))
  		goto efault;

  	if (	__put_user(d_ino, &dirent->d_ino) ||

  		__put_user(offset, &dirent->d_offset) ||
  		__put_user(namlen, &dirent->d_namlen) ||
  		__copy_to_user(dirent->d_name, name, namlen) ||
  		__put_user(0, dirent->d_name + namlen))
  		goto efault;
  	return 0;
  efault:
  	buf->result = -EFAULT;
  	return -EFAULT;
  }

  SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
  		struct old_linux_dirent __user *, dirent, unsigned int, count)

  {
  	int error;

  	struct fd f = fdget_pos(fd);

  	struct readdir_callback buf = {
  		.ctx.actor = fillonedir,
  		.dirent = dirent
  	};

  	if (!f.file)

  		return -EBADF;

  	error = iterate_dir(f.file, &buf.ctx);

  	if (buf.result)

  		error = buf.result;

  	fdput_pos(f);

  	return error;
  }
  
  #endif /* __ARCH_WANT_OLD_READDIR */
  
  /*
   * New, all-improved, singing, dancing, iBCS2-compliant getdents()
   * interface. 
   */
  struct linux_dirent {
  	unsigned long	d_ino;
  	unsigned long	d_off;
  	unsigned short	d_reclen;
  	char		d_name[1];
  };
  
  struct getdents_callback {

  	struct dir_context ctx;

  	struct linux_dirent __user * current_dir;

  	int prev_reclen;

  	int count;
  	int error;
  };

  static int filldir(struct dir_context *ctx, const char *name, int namlen,
  		   loff_t offset, u64 ino, unsigned int d_type)

  {

  	struct linux_dirent __user *dirent, *prev;

  	struct getdents_callback *buf =
  		container_of(ctx, struct getdents_callback, ctx);

  	unsigned long d_ino;

  	int reclen = ALIGN(offsetof(struct linux_dirent, d_name) + namlen + 2,
  		sizeof(long));

  	int prev_reclen;

  	buf->error = verify_dirent_name(name, namlen);
  	if (unlikely(buf->error))
  		return buf->error;

  	buf->error = -EINVAL;	/* only used if we fail.. */
  	if (reclen > buf->count)
  		return -EINVAL;

  	d_ino = ino;

  	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
  		buf->error = -EOVERFLOW;

  		return -EOVERFLOW;

  	}

  	prev_reclen = buf->prev_reclen;
  	if (prev_reclen && signal_pending(current))

  		return -EINTR;

  	dirent = buf->current_dir;

  	prev = (void __user *) dirent - prev_reclen;
  	if (!user_access_begin(prev, reclen + prev_reclen))
  		goto efault;
  
  	/* This might be 'dirent->d_off', but if so it will get overwritten */
  	unsafe_put_user(offset, &prev->d_off, efault_end);

  	unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
  	unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
  	unsafe_put_user(d_type, (char __user *) dirent + reclen - 1, efault_end);
  	unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
  	user_access_end();

  	buf->current_dir = (void __user *)dirent + reclen;
  	buf->prev_reclen = reclen;

  	buf->count -= reclen;
  	return 0;

  efault_end:
  	user_access_end();

  efault:
  	buf->error = -EFAULT;
  	return -EFAULT;
  }

  SYSCALL_DEFINE3(getdents, unsigned int, fd,
  		struct linux_dirent __user *, dirent, unsigned int, count)

  {

  	struct fd f;

  	struct getdents_callback buf = {
  		.ctx.actor = filldir,
  		.count = count,
  		.current_dir = dirent
  	};

  	int error;

  	if (!access_ok(dirent, count))

  		return -EFAULT;

  	f = fdget_pos(fd);

  	if (!f.file)

  		return -EBADF;

  	error = iterate_dir(f.file, &buf.ctx);

  	if (error >= 0)
  		error = buf.error;

  	if (buf.prev_reclen) {
  		struct linux_dirent __user * lastdirent;
  		lastdirent = (void __user *)buf.current_dir - buf.prev_reclen;

  		if (put_user(buf.ctx.pos, &lastdirent->d_off))

  			error = -EFAULT;
  		else
  			error = count - buf.count;
  	}

  	fdput_pos(f);

  	return error;
  }

  struct getdents_callback64 {

  	struct dir_context ctx;

  	struct linux_dirent64 __user * current_dir;

  	int prev_reclen;

  	int count;
  	int error;
  };

  static int filldir64(struct dir_context *ctx, const char *name, int namlen,
  		     loff_t offset, u64 ino, unsigned int d_type)

  {

  	struct linux_dirent64 __user *dirent, *prev;

  	struct getdents_callback64 *buf =
  		container_of(ctx, struct getdents_callback64, ctx);

  	int reclen = ALIGN(offsetof(struct linux_dirent64, d_name) + namlen + 1,
  		sizeof(u64));

  	int prev_reclen;

  	buf->error = verify_dirent_name(name, namlen);
  	if (unlikely(buf->error))
  		return buf->error;

  	buf->error = -EINVAL;	/* only used if we fail.. */
  	if (reclen > buf->count)
  		return -EINVAL;

  	prev_reclen = buf->prev_reclen;
  	if (prev_reclen && signal_pending(current))

  		return -EINTR;

  	dirent = buf->current_dir;

  	prev = (void __user *)dirent - prev_reclen;
  	if (!user_access_begin(prev, reclen + prev_reclen))
  		goto efault;
  
  	/* This might be 'dirent->d_off', but if so it will get overwritten */
  	unsafe_put_user(offset, &prev->d_off, efault_end);

  	unsafe_put_user(ino, &dirent->d_ino, efault_end);
  	unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
  	unsafe_put_user(d_type, &dirent->d_type, efault_end);
  	unsafe_copy_dirent_name(dirent->d_name, name, namlen, efault_end);
  	user_access_end();

  	buf->prev_reclen = reclen;
  	buf->current_dir = (void __user *)dirent + reclen;

  	buf->count -= reclen;
  	return 0;

  efault_end:
  	user_access_end();

  efault:
  	buf->error = -EFAULT;
  	return -EFAULT;
  }

  int ksys_getdents64(unsigned int fd, struct linux_dirent64 __user *dirent,
  		    unsigned int count)

  {

  	struct fd f;

  	struct getdents_callback64 buf = {
  		.ctx.actor = filldir64,
  		.count = count,
  		.current_dir = dirent
  	};

  	int error;

  	if (!access_ok(dirent, count))

  		return -EFAULT;

  	f = fdget_pos(fd);

  	if (!f.file)

  		return -EBADF;

  	error = iterate_dir(f.file, &buf.ctx);

  	if (error >= 0)
  		error = buf.error;

  	if (buf.prev_reclen) {
  		struct linux_dirent64 __user * lastdirent;

  		typeof(lastdirent->d_off) d_off = buf.ctx.pos;

  
  		lastdirent = (void __user *) buf.current_dir - buf.prev_reclen;

  		if (__put_user(d_off, &lastdirent->d_off))

  			error = -EFAULT;
  		else
  			error = count - buf.count;

  	}

  	fdput_pos(f);

  	return error;
  }

  
  SYSCALL_DEFINE3(getdents64, unsigned int, fd,
  		struct linux_dirent64 __user *, dirent, unsigned int, count)
  {
  	return ksys_getdents64(fd, dirent, count);
  }

  #ifdef CONFIG_COMPAT
  struct compat_old_linux_dirent {
  	compat_ulong_t	d_ino;
  	compat_ulong_t	d_offset;
  	unsigned short	d_namlen;
  	char		d_name[1];
  };
  
  struct compat_readdir_callback {
  	struct dir_context ctx;
  	struct compat_old_linux_dirent __user *dirent;
  	int result;
  };
  
  static int compat_fillonedir(struct dir_context *ctx, const char *name,
  			     int namlen, loff_t offset, u64 ino,
  			     unsigned int d_type)
  {
  	struct compat_readdir_callback *buf =
  		container_of(ctx, struct compat_readdir_callback, ctx);
  	struct compat_old_linux_dirent __user *dirent;
  	compat_ulong_t d_ino;
  
  	if (buf->result)
  		return -EINVAL;
  	d_ino = ino;
  	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
  		buf->result = -EOVERFLOW;
  		return -EOVERFLOW;
  	}
  	buf->result++;
  	dirent = buf->dirent;

  	if (!access_ok(dirent,

  			(unsigned long)(dirent->d_name + namlen + 1) -
  				(unsigned long)dirent))
  		goto efault;
  	if (	__put_user(d_ino, &dirent->d_ino) ||
  		__put_user(offset, &dirent->d_offset) ||
  		__put_user(namlen, &dirent->d_namlen) ||
  		__copy_to_user(dirent->d_name, name, namlen) ||
  		__put_user(0, dirent->d_name + namlen))
  		goto efault;
  	return 0;
  efault:
  	buf->result = -EFAULT;
  	return -EFAULT;
  }
  
  COMPAT_SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
  		struct compat_old_linux_dirent __user *, dirent, unsigned int, count)
  {
  	int error;
  	struct fd f = fdget_pos(fd);
  	struct compat_readdir_callback buf = {
  		.ctx.actor = compat_fillonedir,
  		.dirent = dirent
  	};
  
  	if (!f.file)
  		return -EBADF;
  
  	error = iterate_dir(f.file, &buf.ctx);
  	if (buf.result)
  		error = buf.result;
  
  	fdput_pos(f);
  	return error;
  }
  
  struct compat_linux_dirent {
  	compat_ulong_t	d_ino;
  	compat_ulong_t	d_off;
  	unsigned short	d_reclen;
  	char		d_name[1];
  };
  
  struct compat_getdents_callback {
  	struct dir_context ctx;
  	struct compat_linux_dirent __user *current_dir;
  	struct compat_linux_dirent __user *previous;
  	int count;
  	int error;
  };
  
  static int compat_filldir(struct dir_context *ctx, const char *name, int namlen,
  		loff_t offset, u64 ino, unsigned int d_type)
  {
  	struct compat_linux_dirent __user * dirent;
  	struct compat_getdents_callback *buf =
  		container_of(ctx, struct compat_getdents_callback, ctx);
  	compat_ulong_t d_ino;
  	int reclen = ALIGN(offsetof(struct compat_linux_dirent, d_name) +
  		namlen + 2, sizeof(compat_long_t));
  
  	buf->error = -EINVAL;	/* only used if we fail.. */
  	if (reclen > buf->count)
  		return -EINVAL;
  	d_ino = ino;
  	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
  		buf->error = -EOVERFLOW;
  		return -EOVERFLOW;
  	}
  	dirent = buf->previous;
  	if (dirent) {
  		if (signal_pending(current))
  			return -EINTR;
  		if (__put_user(offset, &dirent->d_off))
  			goto efault;
  	}
  	dirent = buf->current_dir;
  	if (__put_user(d_ino, &dirent->d_ino))
  		goto efault;
  	if (__put_user(reclen, &dirent->d_reclen))
  		goto efault;
  	if (copy_to_user(dirent->d_name, name, namlen))
  		goto efault;
  	if (__put_user(0, dirent->d_name + namlen))
  		goto efault;
  	if (__put_user(d_type, (char  __user *) dirent + reclen - 1))
  		goto efault;
  	buf->previous = dirent;
  	dirent = (void __user *)dirent + reclen;
  	buf->current_dir = dirent;
  	buf->count -= reclen;
  	return 0;
  efault:
  	buf->error = -EFAULT;
  	return -EFAULT;
  }
  
  COMPAT_SYSCALL_DEFINE3(getdents, unsigned int, fd,
  		struct compat_linux_dirent __user *, dirent, unsigned int, count)
  {
  	struct fd f;
  	struct compat_linux_dirent __user * lastdirent;
  	struct compat_getdents_callback buf = {
  		.ctx.actor = compat_filldir,
  		.current_dir = dirent,
  		.count = count
  	};
  	int error;

  	if (!access_ok(dirent, count))

  		return -EFAULT;
  
  	f = fdget_pos(fd);
  	if (!f.file)
  		return -EBADF;
  
  	error = iterate_dir(f.file, &buf.ctx);
  	if (error >= 0)
  		error = buf.error;
  	lastdirent = buf.previous;
  	if (lastdirent) {
  		if (put_user(buf.ctx.pos, &lastdirent->d_off))
  			error = -EFAULT;
  		else
  			error = count - buf.count;
  	}
  	fdput_pos(f);
  	return error;
  }
  #endif