// 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)
{
        struct squashfs_sb_info *msblk = sb->s_fs_info;
        int i, length = 0, err;
        unsigned int size;
        struct squashfs_dir_index *index;

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

        index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
        if (index == NULL) {
                ERROR("Failed to allocate squashfs_dir_index\n");
                goto out;
        }

        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, name) > 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);

        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
};