// 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>
 *
 * export.c
 */

/*
 * This file implements code to make Squashfs filesystems exportable (NFS etc.)
 *
 * The export code uses an inode lookup table to map inode numbers passed in
 * filehandles to an inode location on disk.  This table is stored compressed
 * into metadata blocks.  A second index table is used to locate these.  This
 * second index table for speed of access (and because it is small) is read at
 * mount time and cached in memory.
 *
 * The inode lookup table is used only by the export code, inode disk
 * locations are directly encoded in directories, enabling direct access
 * without an intermediate lookup for all operations except the export ops.
 */

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

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

/*
 * Look-up inode number (ino) in table, returning the inode location.
 */
static long long squashfs_inode_lookup(struct super_block *sb, int ino_num)
{
        struct squashfs_sb_info *msblk = sb->s_fs_info;
        int blk = SQUASHFS_LOOKUP_BLOCK(ino_num - 1);
        int offset = SQUASHFS_LOOKUP_BLOCK_OFFSET(ino_num - 1);
        u64 start;
        __le64 ino;
        int err;

        TRACE("Entered squashfs_inode_lookup, inode_number = %d\n", ino_num);

        if (ino_num == 0 || (ino_num - 1) >= msblk->inodes)
                return -EINVAL;

        start = le64_to_cpu(msblk->inode_lookup_table[blk]);

        err = squashfs_read_metadata(sb, &ino, &start, &offset, sizeof(ino));
        if (err < 0)
                return err;

        TRACE("squashfs_inode_lookup, inode = 0x%llx\n",
                (u64) le64_to_cpu(ino));

        return le64_to_cpu(ino);
}


static struct dentry *squashfs_export_iget(struct super_block *sb,
        unsigned int ino_num)
{
        long long ino;
        struct dentry *dentry = ERR_PTR(-ENOENT);

        TRACE("Entered squashfs_export_iget\n");

        ino = squashfs_inode_lookup(sb, ino_num);
        if (ino >= 0)
                dentry = d_obtain_alias(squashfs_iget(sb, ino, ino_num));

        return dentry;
}


static struct dentry *squashfs_fh_to_dentry(struct super_block *sb,
                struct fid *fid, int fh_len, int fh_type)
{
        if ((fh_type != FILEID_INO32_GEN && fh_type != FILEID_INO32_GEN_PARENT)
                        || fh_len < 2)
                return NULL;

        return squashfs_export_iget(sb, fid->i32.ino);
}


static struct dentry *squashfs_fh_to_parent(struct super_block *sb,
                struct fid *fid, int fh_len, int fh_type)
{
        if (fh_type != FILEID_INO32_GEN_PARENT || fh_len < 4)
                return NULL;

        return squashfs_export_iget(sb, fid->i32.parent_ino);
}


static struct dentry *squashfs_get_parent(struct dentry *child)
{
        struct inode *inode = d_inode(child);
        unsigned int parent_ino = squashfs_i(inode)->parent;

        return squashfs_export_iget(inode->i_sb, parent_ino);
}


/*
 * Read uncompressed inode lookup table indexes off disk into memory
 */
__le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
                u64 lookup_table_start, u64 next_table, unsigned int inodes)
{
        unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
        unsigned int indexes = SQUASHFS_LOOKUP_BLOCKS(inodes);
        int n;
        __le64 *table;
        u64 start, end;

        TRACE("In read_inode_lookup_table, length %d\n", length);

        /* Sanity check values */

        /* there should always be at least one inode */
        if (inodes == 0)
                return ERR_PTR(-EINVAL);

        /*
         * The computed size of the lookup table (length bytes) should exactly
         * match the table start and end points
         */
        if (length != (next_table - lookup_table_start))
                return ERR_PTR(-EINVAL);

        table = squashfs_read_table(sb, lookup_table_start, length);
        if (IS_ERR(table))
                return table;

        /*
         * table0], table[1], ... table[indexes - 1] store the locations
         * of the compressed inode lookup blocks.  Each entry should be
         * less than the next (i.e. table[0] < table[1]), and the difference
         * between them should be SQUASHFS_METADATA_SIZE or less.
         * table[indexes - 1] should  be less than lookup_table_start, and
         * again the difference should be SQUASHFS_METADATA_SIZE or less
         */
        for (n = 0; n < (indexes - 1); n++) {
                start = le64_to_cpu(table[n]);
                end = le64_to_cpu(table[n + 1]);

                if (start >= end
                    || (end - start) >
                    (SQUASHFS_METADATA_SIZE + SQUASHFS_BLOCK_OFFSET)) {
                        kfree(table);
                        return ERR_PTR(-EINVAL);
                }
        }

        start = le64_to_cpu(table[indexes - 1]);
        if (start >= lookup_table_start ||
            (lookup_table_start - start) >
            (SQUASHFS_METADATA_SIZE + SQUASHFS_BLOCK_OFFSET)) {
                kfree(table);
                return ERR_PTR(-EINVAL);
        }

        return table;
}


const struct export_operations squashfs_export_ops = {
        .fh_to_dentry = squashfs_fh_to_dentry,
        .fh_to_parent = squashfs_fh_to_parent,
        .get_parent = squashfs_get_parent
};