fs/squashfs/export.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Squashfs - a compressed read only filesystem for Linux
   4  *
   5  * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   6  * Phillip Lougher <phillip@squashfs.org.uk>
   7  *
   8  * export.c
   9  */
  10
  11 /*
  12  * This file implements code to make Squashfs filesystems exportable (NFS etc.)
  13  *
  14  * The export code uses an inode lookup table to map inode numbers passed in
  15  * filehandles to an inode location on disk.  This table is stored compressed
  16  * into metadata blocks.  A second index table is used to locate these.  This
  17  * second index table for speed of access (and because it is small) is read at
  18  * mount time and cached in memory.
  19  *
  20  * The inode lookup table is used only by the export code, inode disk
  21  * locations are directly encoded in directories, enabling direct access
  22  * without an intermediate lookup for all operations except the export ops.
  23  */
  24
  25 #include <linux/fs.h>
  26 #include <linux/vfs.h>
  27 #include <linux/dcache.h>
  28 #include <linux/exportfs.h>
  29 #include <linux/slab.h>
  30
  31 #include "squashfs_fs.h"
  32 #include "squashfs_fs_sb.h"
  33 #include "squashfs_fs_i.h"
  34 #include "squashfs.h"
  35
  36 /*
  37  * Look-up inode number (ino) in table, returning the inode location.
  38  */
  39 static long long squashfs_inode_lookup(struct super_block *sb, int ino_num)
  40 {
  41         struct squashfs_sb_info *msblk = sb->s_fs_info;
  42         int blk = SQUASHFS_LOOKUP_BLOCK(ino_num - 1);
  43         int offset = SQUASHFS_LOOKUP_BLOCK_OFFSET(ino_num - 1);
  44         u64 start = le64_to_cpu(msblk->inode_lookup_table[blk]);
  45         __le64 ino;
  46         int err;
  47
  48         TRACE("Entered squashfs_inode_lookup, inode_number = %d\n", ino_num);
  49
  50         err = squashfs_read_metadata(sb, &ino, &start, &offset, sizeof(ino));
  51         if (err < 0)
  52                 return err;
  53
  54         TRACE("squashfs_inode_lookup, inode = 0x%llx\n",
  55                 (u64) le64_to_cpu(ino));
  56
  57         return le64_to_cpu(ino);
  58 }
  59
  60
  61 static struct dentry *squashfs_export_iget(struct super_block *sb,
  62         unsigned int ino_num)
  63 {
  64         long long ino;
  65         struct dentry *dentry = ERR_PTR(-ENOENT);
  66
  67         TRACE("Entered squashfs_export_iget\n");
  68
  69         ino = squashfs_inode_lookup(sb, ino_num);
  70         if (ino >= 0)
  71                 dentry = d_obtain_alias(squashfs_iget(sb, ino, ino_num));
  72
  73         return dentry;
  74 }
  75
  76
  77 static struct dentry *squashfs_fh_to_dentry(struct super_block *sb,
  78                 struct fid *fid, int fh_len, int fh_type)
  79 {
  80         if ((fh_type != FILEID_INO32_GEN && fh_type != FILEID_INO32_GEN_PARENT)
  81                         || fh_len < 2)
  82                 return NULL;
  83
  84         return squashfs_export_iget(sb, fid->i32.ino);
  85 }
  86
  87
  88 static struct dentry *squashfs_fh_to_parent(struct super_block *sb,
  89                 struct fid *fid, int fh_len, int fh_type)
  90 {
  91         if (fh_type != FILEID_INO32_GEN_PARENT || fh_len < 4)
  92                 return NULL;
  93
  94         return squashfs_export_iget(sb, fid->i32.parent_ino);
  95 }
  96
  97
  98 static struct dentry *squashfs_get_parent(struct dentry *child)
  99 {
 100         struct inode *inode = d_inode(child);
 101         unsigned int parent_ino = squashfs_i(inode)->parent;
 102
 103         return squashfs_export_iget(inode->i_sb, parent_ino);
 104 }
 105
 106
 107 /*
 108  * Read uncompressed inode lookup table indexes off disk into memory
 109  */
 110 __le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
 111                 u64 lookup_table_start, u64 next_table, unsigned int inodes)
 112 {
 113         unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
 114         __le64 *table;
 115
 116         TRACE("In read_inode_lookup_table, length %d\n", length);
 117
 118         /* Sanity check values */
 119
 120         /* there should always be at least one inode */
 121         if (inodes == 0)
 122                 return ERR_PTR(-EINVAL);
 123
 124         /* length bytes should not extend into the next table - this check
 125          * also traps instances where lookup_table_start is incorrectly larger
 126          * than the next table start
 127          */
 128         if (lookup_table_start + length > next_table)
 129                 return ERR_PTR(-EINVAL);
 130
 131         table = squashfs_read_table(sb, lookup_table_start, length);
 132
 133         /*
 134          * table[0] points to the first inode lookup table metadata block,
 135          * this should be less than lookup_table_start
 136          */
 137         if (!IS_ERR(table) && le64_to_cpu(table[0]) >= lookup_table_start) {
 138                 kfree(table);
 139                 return ERR_PTR(-EINVAL);
 140         }
 141
 142         return table;
 143 }
 144
 145
 146 const struct export_operations squashfs_export_ops = {
 147         .fh_to_dentry = squashfs_fh_to_dentry,
 148         .fh_to_parent = squashfs_fh_to_parent,
 149         .get_parent = squashfs_get_parent
 150 };