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;
  45         __le64 ino;
  46         int err;
  47
  48         TRACE("Entered squashfs_inode_lookup, inode_number = %d\n", ino_num);
  49
  50         if (ino_num == 0 || (ino_num - 1) >= msblk->inodes)
  51                 return -EINVAL;
  52
  53         start = le64_to_cpu(msblk->inode_lookup_table[blk]);
  54
  55         err = squashfs_read_metadata(sb, &ino, &start, &offset, sizeof(ino));
  56         if (err < 0)
  57                 return err;
  58
  59         TRACE("squashfs_inode_lookup, inode = 0x%llx\n",
  60                 (u64) le64_to_cpu(ino));
  61
  62         return le64_to_cpu(ino);
  63 }
  64
  65
  66 static struct dentry *squashfs_export_iget(struct super_block *sb,
  67         unsigned int ino_num)
  68 {
  69         long long ino;
  70         struct dentry *dentry = ERR_PTR(-ENOENT);
  71
  72         TRACE("Entered squashfs_export_iget\n");
  73
  74         ino = squashfs_inode_lookup(sb, ino_num);
  75         if (ino >= 0)
  76                 dentry = d_obtain_alias(squashfs_iget(sb, ino, ino_num));
  77
  78         return dentry;
  79 }
  80
  81
  82 static struct dentry *squashfs_fh_to_dentry(struct super_block *sb,
  83                 struct fid *fid, int fh_len, int fh_type)
  84 {
  85         if ((fh_type != FILEID_INO32_GEN && fh_type != FILEID_INO32_GEN_PARENT)
  86                         || fh_len < 2)
  87                 return NULL;
  88
  89         return squashfs_export_iget(sb, fid->i32.ino);
  90 }
  91
  92
  93 static struct dentry *squashfs_fh_to_parent(struct super_block *sb,
  94                 struct fid *fid, int fh_len, int fh_type)
  95 {
  96         if (fh_type != FILEID_INO32_GEN_PARENT || fh_len < 4)
  97                 return NULL;
  98
  99         return squashfs_export_iget(sb, fid->i32.parent_ino);
 100 }
 101
 102
 103 static struct dentry *squashfs_get_parent(struct dentry *child)
 104 {
 105         struct inode *inode = d_inode(child);
 106         unsigned int parent_ino = squashfs_i(inode)->parent;
 107
 108         return squashfs_export_iget(inode->i_sb, parent_ino);
 109 }
 110
 111
 112 /*
 113  * Read uncompressed inode lookup table indexes off disk into memory
 114  */
 115 __le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
 116                 u64 lookup_table_start, u64 next_table, unsigned int inodes)
 117 {
 118         unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
 119         unsigned int indexes = SQUASHFS_LOOKUP_BLOCKS(inodes);
 120         int n;
 121         __le64 *table;
 122         u64 start, end;
 123
 124         TRACE("In read_inode_lookup_table, length %d\n", length);
 125
 126         /* Sanity check values */
 127
 128         /* there should always be at least one inode */
 129         if (inodes == 0)
 130                 return ERR_PTR(-EINVAL);
 131
 132         /*
 133          * The computed size of the lookup table (length bytes) should exactly
 134          * match the table start and end points
 135          */
 136         if (length != (next_table - lookup_table_start))
 137                 return ERR_PTR(-EINVAL);
 138
 139         table = squashfs_read_table(sb, lookup_table_start, length);
 140         if (IS_ERR(table))
 141                 return table;
 142
 143         /*
 144          * table0], table[1], ... table[indexes - 1] store the locations
 145          * of the compressed inode lookup blocks.  Each entry should be
 146          * less than the next (i.e. table[0] < table[1]), and the difference
 147          * between them should be SQUASHFS_METADATA_SIZE or less.
 148          * table[indexes - 1] should  be less than lookup_table_start, and
 149          * again the difference should be SQUASHFS_METADATA_SIZE or less
 150          */
 151         for (n = 0; n < (indexes - 1); n++) {
 152                 start = le64_to_cpu(table[n]);
 153                 end = le64_to_cpu(table[n + 1]);
 154
 155                 if (start >= end
 156                     || (end - start) >
 157                     (SQUASHFS_METADATA_SIZE + SQUASHFS_BLOCK_OFFSET)) {
 158                         kfree(table);
 159                         return ERR_PTR(-EINVAL);
 160                 }
 161         }
 162
 163         start = le64_to_cpu(table[indexes - 1]);
 164         if (start >= lookup_table_start ||
 165             (lookup_table_start - start) >
 166             (SQUASHFS_METADATA_SIZE + SQUASHFS_BLOCK_OFFSET)) {
 167                 kfree(table);
 168                 return ERR_PTR(-EINVAL);
 169         }
 170
 171         return table;
 172 }
 173
 174
 175 const struct export_operations squashfs_export_ops = {
 176         .encode_fh = generic_encode_ino32_fh,
 177         .fh_to_dentry = squashfs_fh_to_dentry,
 178         .fh_to_parent = squashfs_fh_to_parent,
 179         .get_parent = squashfs_get_parent
 180 };