linux_kernel/fs/squashfs/namei.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <phillip@squashfs.org.uk>
 *
 * namei.c
 */

/*
 * This file implements code to do filename lookup in directories.
 *
 * Like inodes, directories are packed into compressed metadata blocks, stored
 * in a directory table.  Directories are accessed using the start address of
 * the metablock containing the directory and the offset into the
 * decompressed block (<block, offset>).
 *
 * Directories are organised in a slightly complex way, and are not simply
 * a list of file names.  The organisation takes advantage of the
 * fact that (in most cases) the inodes of the files will be in the same
 * compressed metadata block, and therefore, can share the start block.
 * Directories are therefore organised in a two level list, a directory
 * header containing the shared start block value, and a sequence of directory
 * entries, each of which share the shared start block.  A new directory header
 * is written once/if the inode start block changes.  The directory
 * header/directory entry list is repeated as many times as necessary.
 *
 * Directories are sorted, and can contain a directory index to speed up
 * file lookup.  Directory indexes store one entry per metablock, each entry
 * storing the index/filename mapping to the first directory header
 * in each metadata block.  Directories are sorted in alphabetical order,
 * and at lookup the index is scanned linearly looking for the first filename
 * alphabetically larger than the filename being looked up.  At this point the
 * location of the metadata block the filename is in has been found.
 * The general idea of the index is ensure only one metadata block needs to be
 * decompressed to do a lookup irrespective of the length of the directory.
 * This scheme has the advantage that it doesn't require extra memory overhead
 * and doesn't require much extra storage on disk.
 */

#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/dcache.h>
#include <linux/xattr.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"
#include "xattr.h"

/*
 * Lookup name in the directory index, returning the location of the metadata
 * block containing it, and the directory index this represents.
 *
 * If we get an error reading the index then return the part of the index
 * (if any) we have managed to read - the index isn't essential, just
 * quicker.
 */
static int get_dir_index_using_name(struct super_block *sb,
			u64 *next_block, int *next_offset, u64 index_start,
			int index_offset, int i_count, const char *name,
			int len)
{
	struct squashfs_sb_info *msblk = sb->s_fs_info;
	int i, length = 0, err;
	unsigned int size;
	struct squashfs_dir_index *index;
	char *str;

	TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);

	index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
	if (index == NULL) {
		ERROR("Failed to allocate squashfs_dir_index\n");
		goto out;
	}

	str = &index->name[SQUASHFS_NAME_LEN + 1];
	strncpy(str, name, len);
	str[len] = '\0';

	for (i = 0; i < i_count; i++) {
		err = squashfs_read_metadata(sb, index, &index_start,
					&index_offset, sizeof(*index));
		if (err < 0)
			break;


		size = le32_to_cpu(index->size) + 1;
		if (size > SQUASHFS_NAME_LEN)
			break;

		err = squashfs_read_metadata(sb, index->name, &index_start,
					&index_offset, size);
		if (err < 0)
			break;

		index->name[size] = '\0';

		if (strcmp(index->name, str) > 0)
			break;

		length = le32_to_cpu(index->index);
		*next_block = le32_to_cpu(index->start_block) +
					msblk->directory_table;
	}

	*next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
	kfree(index);

out:
	/*
	 * Return index (f_pos) of the looked up metadata block.  Translate
	 * from internal f_pos to external f_pos which is offset by 3 because
	 * we invent "." and ".." entries which are not actually stored in the
	 * directory.
	 */
	return length + 3;
}


static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
				 unsigned int flags)
{
	const unsigned char *name = dentry->d_name.name;
	int len = dentry->d_name.len;
	struct inode *inode = NULL;
	struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
	struct squashfs_dir_header dirh;
	struct squashfs_dir_entry *dire;
	u64 block = squashfs_i(dir)->start + msblk->directory_table;
	int offset = squashfs_i(dir)->offset;
	int err, length;
	unsigned int dir_count, size;

	TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);

	dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
	if (dire == NULL) {
		ERROR("Failed to allocate squashfs_dir_entry\n");
		return ERR_PTR(-ENOMEM);
	}

	if (len > SQUASHFS_NAME_LEN) {
		err = -ENAMETOOLONG;
		goto failed;
	}

	length = get_dir_index_using_name(dir->i_sb, &block, &offset,
				squashfs_i(dir)->dir_idx_start,
				squashfs_i(dir)->dir_idx_offset,
				squashfs_i(dir)->dir_idx_cnt, name, len);

	while (length < i_size_read(dir)) {
		/*
		 * Read directory header.
		 */
		err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
				&offset, sizeof(dirh));
		if (err < 0)
			goto read_failure;

		length += sizeof(dirh);

		dir_count = le32_to_cpu(dirh.count) + 1;

		if (dir_count > SQUASHFS_DIR_COUNT)
			goto data_error;

		while (dir_count--) {
			/*
			 * Read directory entry.
			 */
			err = squashfs_read_metadata(dir->i_sb, dire, &block,
					&offset, sizeof(*dire));
			if (err < 0)
				goto read_failure;

			size = le16_to_cpu(dire->size) + 1;

			/* size should never be larger than SQUASHFS_NAME_LEN */
			if (size > SQUASHFS_NAME_LEN)
				goto data_error;

			err = squashfs_read_metadata(dir->i_sb, dire->name,
					&block, &offset, size);
			if (err < 0)
				goto read_failure;

			length += sizeof(*dire) + size;

			if (name[0] < dire->name[0])
				goto exit_lookup;

			if (len == size && !strncmp(name, dire->name, len)) {
				unsigned int blk, off, ino_num;
				long long ino;
				blk = le32_to_cpu(dirh.start_block);
				off = le16_to_cpu(dire->offset);
				ino_num = le32_to_cpu(dirh.inode_number) +
					(short) le16_to_cpu(dire->inode_number);
				ino = SQUASHFS_MKINODE(blk, off);

				TRACE("calling squashfs_iget for directory "
					"entry %s, inode  %x:%x, %d\n", name,
					blk, off, ino_num);

				inode = squashfs_iget(dir->i_sb, ino, ino_num);
				goto exit_lookup;
			}
		}
	}

exit_lookup:
	kfree(dire);
	return d_splice_alias(inode, dentry);

data_error:
	err = -EIO;

read_failure:
	ERROR("Unable to read directory block [%llx:%x]\n",
		squashfs_i(dir)->start + msblk->directory_table,
		squashfs_i(dir)->offset);
failed:
	kfree(dire);
	return ERR_PTR(err);
}


const struct inode_operations squashfs_dir_inode_ops = {
	.lookup = squashfs_lookup,
	.listxattr = squashfs_listxattr
};