fs/ext4/verity.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fs/ext4/verity.c: fs-verity support for ext4
   4  *
   5  * Copyright 2019 Google LLC
   6  */
   7
   8 /*
   9  * Implementation of fsverity_operations for ext4.
  10  *
  11  * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past
  12  * the end of the file, starting at the first 64K boundary beyond i_size.  This
  13  * approach works because (a) verity files are readonly, and (b) pages fully
  14  * beyond i_size aren't visible to userspace but can be read/written internally
  15  * by ext4 with only some relatively small changes to ext4.  This approach
  16  * avoids having to depend on the EA_INODE feature and on rearchitecturing
  17  * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and
  18  * to support encrypting xattrs.  Note that the verity metadata *must* be
  19  * encrypted when the file is, since it contains hashes of the plaintext data.
  20  *
  21  * Using a 64K boundary rather than a 4K one keeps things ready for
  22  * architectures with 64K pages, and it doesn't necessarily waste space on-disk
  23  * since there can be a hole between i_size and the start of the Merkle tree.
  24  */
  25
  26 #include <linux/quotaops.h>
  27
  28 #include "ext4.h"
  29 #include "ext4_extents.h"
  30 #include "ext4_jbd2.h"
  31
  32 static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)
  33 {
  34         return round_up(inode->i_size, 65536);
  35 }
  36
  37 /*
  38  * Read some verity metadata from the inode.  __vfs_read() can't be used because
  39  * we need to read beyond i_size.
  40  */
  41 static int pagecache_read(struct inode *inode, void *buf, size_t count,
  42                           loff_t pos)
  43 {
  44         while (count) {
  45                 struct folio *folio;
  46                 size_t n;
  47
  48                 folio = read_mapping_folio(inode->i_mapping, pos >> PAGE_SHIFT,
  49                                          NULL);
  50                 if (IS_ERR(folio))
  51                         return PTR_ERR(folio);
  52
  53                 n = memcpy_from_file_folio(buf, folio, pos, count);
  54                 folio_put(folio);
  55
  56                 buf += n;
  57                 pos += n;
  58                 count -= n;
  59         }
  60         return 0;
  61 }
  62
  63 /*
  64  * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
  65  * kernel_write() can't be used because the file descriptor is readonly.
  66  */
  67 static int pagecache_write(struct inode *inode, const void *buf, size_t count,
  68                            loff_t pos)
  69 {
  70         struct address_space *mapping = inode->i_mapping;
  71         const struct address_space_operations *aops = mapping->a_ops;
  72
  73         if (pos + count > inode->i_sb->s_maxbytes)
  74                 return -EFBIG;
  75
  76         while (count) {
  77                 size_t n = min_t(size_t, count,
  78                                  PAGE_SIZE - offset_in_page(pos));
  79                 struct folio *folio;
  80                 void *fsdata = NULL;
  81                 int res;
  82
  83                 res = aops->write_begin(NULL, mapping, pos, n, &folio, &fsdata);
  84                 if (res)
  85                         return res;
  86
  87                 memcpy_to_folio(folio, offset_in_folio(folio, pos), buf, n);
  88
  89                 res = aops->write_end(NULL, mapping, pos, n, n, folio, fsdata);
  90                 if (res < 0)
  91                         return res;
  92                 if (res != n)
  93                         return -EIO;
  94
  95                 buf += n;
  96                 pos += n;
  97                 count -= n;
  98         }
  99         return 0;
 100 }
 101
 102 static int ext4_begin_enable_verity(struct file *filp)
 103 {
 104         struct inode *inode = file_inode(filp);
 105         const int credits = 2; /* superblock and inode for ext4_orphan_add() */
 106         handle_t *handle;
 107         int err;
 108
 109         if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX))
 110                 return -EINVAL;
 111
 112         if (ext4_verity_in_progress(inode))
 113                 return -EBUSY;
 114
 115         /*
 116          * Since the file was opened readonly, we have to initialize the jbd
 117          * inode and quotas here and not rely on ->open() doing it.  This must
 118          * be done before evicting the inline data.
 119          */
 120
 121         err = ext4_inode_attach_jinode(inode);
 122         if (err)
 123                 return err;
 124
 125         err = dquot_initialize(inode);
 126         if (err)
 127                 return err;
 128
 129         err = ext4_convert_inline_data(inode);
 130         if (err)
 131                 return err;
 132
 133         if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
 134                 ext4_warning_inode(inode,
 135                                    "verity is only allowed on extent-based files");
 136                 return -EOPNOTSUPP;
 137         }
 138
 139         /*
 140          * ext4 uses the last allocated block to find the verity descriptor, so
 141          * we must remove any other blocks past EOF which might confuse things.
 142          */
 143         err = ext4_truncate(inode);
 144         if (err)
 145                 return err;
 146
 147         handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
 148         if (IS_ERR(handle))
 149                 return PTR_ERR(handle);
 150
 151         err = ext4_orphan_add(handle, inode);
 152         if (err == 0)
 153                 ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
 154
 155         ext4_journal_stop(handle);
 156         return err;
 157 }
 158
 159 /*
 160  * ext4 stores the verity descriptor beginning on the next filesystem block
 161  * boundary after the Merkle tree.  Then, the descriptor size is stored in the
 162  * last 4 bytes of the last allocated filesystem block --- which is either the
 163  * block in which the descriptor ends, or the next block after that if there
 164  * weren't at least 4 bytes remaining.
 165  *
 166  * We can't simply store the descriptor in an xattr because it *must* be
 167  * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
 168  * xattrs.  Also, if the descriptor includes a large signature blob it may be
 169  * too large to store in an xattr without the EA_INODE feature.
 170  */
 171 static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
 172                                         size_t desc_size, u64 merkle_tree_size)
 173 {
 174         const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
 175                                       merkle_tree_size, i_blocksize(inode));
 176         const u64 desc_end = desc_pos + desc_size;
 177         const __le32 desc_size_disk = cpu_to_le32(desc_size);
 178         const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
 179                                            i_blocksize(inode)) -
 180                                   sizeof(desc_size_disk);
 181         int err;
 182
 183         err = pagecache_write(inode, desc, desc_size, desc_pos);
 184         if (err)
 185                 return err;
 186
 187         return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
 188                                desc_size_pos);
 189 }
 190
 191 static int ext4_end_enable_verity(struct file *filp, const void *desc,
 192                                   size_t desc_size, u64 merkle_tree_size)
 193 {
 194         struct inode *inode = file_inode(filp);
 195         const int credits = 2; /* superblock and inode for ext4_orphan_del() */
 196         handle_t *handle;
 197         struct ext4_iloc iloc;
 198         int err = 0;
 199
 200         /*
 201          * If an error already occurred (which fs/verity/ signals by passing
 202          * desc == NULL), then only clean-up is needed.
 203          */
 204         if (desc == NULL)
 205                 goto cleanup;
 206
 207         /* Append the verity descriptor. */
 208         err = ext4_write_verity_descriptor(inode, desc, desc_size,
 209                                            merkle_tree_size);
 210         if (err)
 211                 goto cleanup;
 212
 213         /*
 214          * Write all pages (both data and verity metadata).  Note that this must
 215          * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages
 216          * beyond i_size won't be written properly.  For crash consistency, this
 217          * also must happen before the verity inode flag gets persisted.
 218          */
 219         err = filemap_write_and_wait(inode->i_mapping);
 220         if (err)
 221                 goto cleanup;
 222
 223         /*
 224          * Finally, set the verity inode flag and remove the inode from the
 225          * orphan list (in a single transaction).
 226          */
 227
 228         handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
 229         if (IS_ERR(handle)) {
 230                 err = PTR_ERR(handle);
 231                 goto cleanup;
 232         }
 233
 234         err = ext4_orphan_del(handle, inode);
 235         if (err)
 236                 goto stop_and_cleanup;
 237
 238         err = ext4_reserve_inode_write(handle, inode, &iloc);
 239         if (err)
 240                 goto stop_and_cleanup;
 241
 242         ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
 243         ext4_set_inode_flags(inode, false);
 244         err = ext4_mark_iloc_dirty(handle, inode, &iloc);
 245         if (err)
 246                 goto stop_and_cleanup;
 247
 248         ext4_journal_stop(handle);
 249
 250         ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
 251         return 0;
 252
 253 stop_and_cleanup:
 254         ext4_journal_stop(handle);
 255 cleanup:
 256         /*
 257          * Verity failed to be enabled, so clean up by truncating any verity
 258          * metadata that was written beyond i_size (both from cache and from
 259          * disk), removing the inode from the orphan list (if it wasn't done
 260          * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS.
 261          */
 262         truncate_inode_pages(inode->i_mapping, inode->i_size);
 263         ext4_truncate(inode);
 264         ext4_orphan_del(NULL, inode);
 265         ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
 266         return err;
 267 }
 268
 269 static int ext4_get_verity_descriptor_location(struct inode *inode,
 270                                                size_t *desc_size_ret,
 271                                                u64 *desc_pos_ret)
 272 {
 273         struct ext4_ext_path *path;
 274         struct ext4_extent *last_extent;
 275         u32 end_lblk;
 276         u64 desc_size_pos;
 277         __le32 desc_size_disk;
 278         u32 desc_size;
 279         u64 desc_pos;
 280         int err;
 281
 282         /*
 283          * Descriptor size is in last 4 bytes of last allocated block.
 284          * See ext4_write_verity_descriptor().
 285          */
 286
 287         if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
 288                 EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
 289                 return -EFSCORRUPTED;
 290         }
 291
 292         path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
 293         if (IS_ERR(path))
 294                 return PTR_ERR(path);
 295
 296         last_extent = path[path->p_depth].p_ext;
 297         if (!last_extent) {
 298                 EXT4_ERROR_INODE(inode, "verity file has no extents");
 299                 ext4_free_ext_path(path);
 300                 return -EFSCORRUPTED;
 301         }
 302
 303         end_lblk = le32_to_cpu(last_extent->ee_block) +
 304                    ext4_ext_get_actual_len(last_extent);
 305         desc_size_pos = (u64)end_lblk << inode->i_blkbits;
 306         ext4_free_ext_path(path);
 307
 308         if (desc_size_pos < sizeof(desc_size_disk))
 309                 goto bad;
 310         desc_size_pos -= sizeof(desc_size_disk);
 311
 312         err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
 313                              desc_size_pos);
 314         if (err)
 315                 return err;
 316         desc_size = le32_to_cpu(desc_size_disk);
 317
 318         /*
 319          * The descriptor is stored just before the desc_size_disk, but starting
 320          * on a filesystem block boundary.
 321          */
 322
 323         if (desc_size > INT_MAX || desc_size > desc_size_pos)
 324                 goto bad;
 325
 326         desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
 327         if (desc_pos < ext4_verity_metadata_pos(inode))
 328                 goto bad;
 329
 330         *desc_size_ret = desc_size;
 331         *desc_pos_ret = desc_pos;
 332         return 0;
 333
 334 bad:
 335         EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
 336         return -EFSCORRUPTED;
 337 }
 338
 339 static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
 340                                       size_t buf_size)
 341 {
 342         size_t desc_size = 0;
 343         u64 desc_pos = 0;
 344         int err;
 345
 346         err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
 347         if (err)
 348                 return err;
 349
 350         if (buf_size) {
 351                 if (desc_size > buf_size)
 352                         return -ERANGE;
 353                 err = pagecache_read(inode, buf, desc_size, desc_pos);
 354                 if (err)
 355                         return err;
 356         }
 357         return desc_size;
 358 }
 359
 360 static struct page *ext4_read_merkle_tree_page(struct inode *inode,
 361                                                pgoff_t index,
 362                                                unsigned long num_ra_pages)
 363 {
 364         struct folio *folio;
 365
 366         index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
 367
 368         folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
 369         if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
 370                 DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
 371
 372                 if (!IS_ERR(folio))
 373                         folio_put(folio);
 374                 else if (num_ra_pages > 1)
 375                         page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
 376                 folio = read_mapping_folio(inode->i_mapping, index, NULL);
 377                 if (IS_ERR(folio))
 378                         return ERR_CAST(folio);
 379         }
 380         return folio_file_page(folio, index);
 381 }
 382
 383 static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
 384                                         u64 pos, unsigned int size)
 385 {
 386         pos += ext4_verity_metadata_pos(inode);
 387
 388         return pagecache_write(inode, buf, size, pos);
 389 }
 390
 391 const struct fsverity_operations ext4_verityops = {
 392         .begin_enable_verity    = ext4_begin_enable_verity,
 393         .end_enable_verity      = ext4_end_enable_verity,
 394         .get_verity_descriptor  = ext4_get_verity_descriptor,
 395         .read_merkle_tree_page  = ext4_read_merkle_tree_page,
 396         .write_merkle_tree_block = ext4_write_merkle_tree_block,
 397 };