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                 size_t n = min_t(size_t, count,
  46                                  PAGE_SIZE - offset_in_page(pos));
  47                 struct page *page;
  48                 void *addr;
  49
  50                 page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
  51                                          NULL);
  52                 if (IS_ERR(page))
  53                         return PTR_ERR(page);
  54
  55                 addr = kmap_atomic(page);
  56                 memcpy(buf, addr + offset_in_page(pos), n);
  57                 kunmap_atomic(addr);
  58
  59                 put_page(page);
  60
  61                 buf += n;
  62                 pos += n;
  63                 count -= n;
  64         }
  65         return 0;
  66 }
  67
  68 /*
  69  * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
  70  * kernel_write() can't be used because the file descriptor is readonly.
  71  */
  72 static int pagecache_write(struct inode *inode, const void *buf, size_t count,
  73                            loff_t pos)
  74 {
  75         if (pos + count > inode->i_sb->s_maxbytes)
  76                 return -EFBIG;
  77
  78         while (count) {
  79                 size_t n = min_t(size_t, count,
  80                                  PAGE_SIZE - offset_in_page(pos));
  81                 struct page *page;
  82                 void *fsdata;
  83                 void *addr;
  84                 int res;
  85
  86                 res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
  87                                             &page, &fsdata);
  88                 if (res)
  89                         return res;
  90
  91                 addr = kmap_atomic(page);
  92                 memcpy(addr + offset_in_page(pos), buf, n);
  93                 kunmap_atomic(addr);
  94
  95                 res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
  96                                           page, fsdata);
  97                 if (res < 0)
  98                         return res;
  99                 if (res != n)
 100                         return -EIO;
 101
 102                 buf += n;
 103                 pos += n;
 104                 count -= n;
 105         }
 106         return 0;
 107 }
 108
 109 static int ext4_begin_enable_verity(struct file *filp)
 110 {
 111         struct inode *inode = file_inode(filp);
 112         const int credits = 2; /* superblock and inode for ext4_orphan_add() */
 113         handle_t *handle;
 114         int err;
 115
 116         if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX))
 117                 return -EINVAL;
 118
 119         if (ext4_verity_in_progress(inode))
 120                 return -EBUSY;
 121
 122         /*
 123          * Since the file was opened readonly, we have to initialize the jbd
 124          * inode and quotas here and not rely on ->open() doing it.  This must
 125          * be done before evicting the inline data.
 126          */
 127
 128         err = ext4_inode_attach_jinode(inode);
 129         if (err)
 130                 return err;
 131
 132         err = dquot_initialize(inode);
 133         if (err)
 134                 return err;
 135
 136         err = ext4_convert_inline_data(inode);
 137         if (err)
 138                 return err;
 139
 140         if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
 141                 ext4_warning_inode(inode,
 142                                    "verity is only allowed on extent-based files");
 143                 return -EOPNOTSUPP;
 144         }
 145
 146         /*
 147          * ext4 uses the last allocated block to find the verity descriptor, so
 148          * we must remove any other blocks past EOF which might confuse things.
 149          */
 150         err = ext4_truncate(inode);
 151         if (err)
 152                 return err;
 153
 154         handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
 155         if (IS_ERR(handle))
 156                 return PTR_ERR(handle);
 157
 158         err = ext4_orphan_add(handle, inode);
 159         if (err == 0)
 160                 ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
 161
 162         ext4_journal_stop(handle);
 163         return err;
 164 }
 165
 166 /*
 167  * ext4 stores the verity descriptor beginning on the next filesystem block
 168  * boundary after the Merkle tree.  Then, the descriptor size is stored in the
 169  * last 4 bytes of the last allocated filesystem block --- which is either the
 170  * block in which the descriptor ends, or the next block after that if there
 171  * weren't at least 4 bytes remaining.
 172  *
 173  * We can't simply store the descriptor in an xattr because it *must* be
 174  * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
 175  * xattrs.  Also, if the descriptor includes a large signature blob it may be
 176  * too large to store in an xattr without the EA_INODE feature.
 177  */
 178 static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
 179                                         size_t desc_size, u64 merkle_tree_size)
 180 {
 181         const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
 182                                       merkle_tree_size, i_blocksize(inode));
 183         const u64 desc_end = desc_pos + desc_size;
 184         const __le32 desc_size_disk = cpu_to_le32(desc_size);
 185         const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
 186                                            i_blocksize(inode)) -
 187                                   sizeof(desc_size_disk);
 188         int err;
 189
 190         err = pagecache_write(inode, desc, desc_size, desc_pos);
 191         if (err)
 192                 return err;
 193
 194         return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
 195                                desc_size_pos);
 196 }
 197
 198 static int ext4_end_enable_verity(struct file *filp, const void *desc,
 199                                   size_t desc_size, u64 merkle_tree_size)
 200 {
 201         struct inode *inode = file_inode(filp);
 202         const int credits = 2; /* superblock and inode for ext4_orphan_del() */
 203         handle_t *handle;
 204         int err = 0;
 205         int err2;
 206
 207         if (desc != NULL) {
 208                 /* Succeeded; write the verity descriptor. */
 209                 err = ext4_write_verity_descriptor(inode, desc, desc_size,
 210                                                    merkle_tree_size);
 211
 212                 /* Write all pages before clearing VERITY_IN_PROGRESS. */
 213                 if (!err)
 214                         err = filemap_write_and_wait(inode->i_mapping);
 215         }
 216
 217         /* If we failed, truncate anything we wrote past i_size. */
 218         if (desc == NULL || err)
 219                 ext4_truncate(inode);
 220
 221         /*
 222          * We must always clean up by clearing EXT4_STATE_VERITY_IN_PROGRESS and
 223          * deleting the inode from the orphan list, even if something failed.
 224          * If everything succeeded, we'll also set the verity bit in the same
 225          * transaction.
 226          */
 227
 228         ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
 229
 230         handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
 231         if (IS_ERR(handle)) {
 232                 ext4_orphan_del(NULL, inode);
 233                 return PTR_ERR(handle);
 234         }
 235
 236         err2 = ext4_orphan_del(handle, inode);
 237         if (err2)
 238                 goto out_stop;
 239
 240         if (desc != NULL && !err) {
 241                 struct ext4_iloc iloc;
 242
 243                 err = ext4_reserve_inode_write(handle, inode, &iloc);
 244                 if (err)
 245                         goto out_stop;
 246                 ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
 247                 ext4_set_inode_flags(inode, false);
 248                 err = ext4_mark_iloc_dirty(handle, inode, &iloc);
 249         }
 250 out_stop:
 251         ext4_journal_stop(handle);
 252         return err ?: err2;
 253 }
 254
 255 static int ext4_get_verity_descriptor_location(struct inode *inode,
 256                                                size_t *desc_size_ret,
 257                                                u64 *desc_pos_ret)
 258 {
 259         struct ext4_ext_path *path;
 260         struct ext4_extent *last_extent;
 261         u32 end_lblk;
 262         u64 desc_size_pos;
 263         __le32 desc_size_disk;
 264         u32 desc_size;
 265         u64 desc_pos;
 266         int err;
 267
 268         /*
 269          * Descriptor size is in last 4 bytes of last allocated block.
 270          * See ext4_write_verity_descriptor().
 271          */
 272
 273         if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
 274                 EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
 275                 return -EFSCORRUPTED;
 276         }
 277
 278         path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
 279         if (IS_ERR(path))
 280                 return PTR_ERR(path);
 281
 282         last_extent = path[path->p_depth].p_ext;
 283         if (!last_extent) {
 284                 EXT4_ERROR_INODE(inode, "verity file has no extents");
 285                 ext4_ext_drop_refs(path);
 286                 kfree(path);
 287                 return -EFSCORRUPTED;
 288         }
 289
 290         end_lblk = le32_to_cpu(last_extent->ee_block) +
 291                    ext4_ext_get_actual_len(last_extent);
 292         desc_size_pos = (u64)end_lblk << inode->i_blkbits;
 293         ext4_ext_drop_refs(path);
 294         kfree(path);
 295
 296         if (desc_size_pos < sizeof(desc_size_disk))
 297                 goto bad;
 298         desc_size_pos -= sizeof(desc_size_disk);
 299
 300         err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
 301                              desc_size_pos);
 302         if (err)
 303                 return err;
 304         desc_size = le32_to_cpu(desc_size_disk);
 305
 306         /*
 307          * The descriptor is stored just before the desc_size_disk, but starting
 308          * on a filesystem block boundary.
 309          */
 310
 311         if (desc_size > INT_MAX || desc_size > desc_size_pos)
 312                 goto bad;
 313
 314         desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
 315         if (desc_pos < ext4_verity_metadata_pos(inode))
 316                 goto bad;
 317
 318         *desc_size_ret = desc_size;
 319         *desc_pos_ret = desc_pos;
 320         return 0;
 321
 322 bad:
 323         EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
 324         return -EFSCORRUPTED;
 325 }
 326
 327 static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
 328                                       size_t buf_size)
 329 {
 330         size_t desc_size = 0;
 331         u64 desc_pos = 0;
 332         int err;
 333
 334         err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
 335         if (err)
 336                 return err;
 337
 338         if (buf_size) {
 339                 if (desc_size > buf_size)
 340                         return -ERANGE;
 341                 err = pagecache_read(inode, buf, desc_size, desc_pos);
 342                 if (err)
 343                         return err;
 344         }
 345         return desc_size;
 346 }
 347
 348 static struct page *ext4_read_merkle_tree_page(struct inode *inode,
 349                                                pgoff_t index,
 350                                                unsigned long num_ra_pages)
 351 {
 352         DEFINE_READAHEAD(ractl, NULL, inode->i_mapping, index);
 353         struct page *page;
 354
 355         index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
 356
 357         page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
 358         if (!page || !PageUptodate(page)) {
 359                 if (page)
 360                         put_page(page);
 361                 else if (num_ra_pages > 1)
 362                         page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
 363                 page = read_mapping_page(inode->i_mapping, index, NULL);
 364         }
 365         return page;
 366 }
 367
 368 static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
 369                                         u64 index, int log_blocksize)
 370 {
 371         loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize);
 372
 373         return pagecache_write(inode, buf, 1 << log_blocksize, pos);
 374 }
 375
 376 const struct fsverity_operations ext4_verityops = {
 377         .begin_enable_verity    = ext4_begin_enable_verity,
 378         .end_enable_verity      = ext4_end_enable_verity,
 379         .get_verity_descriptor  = ext4_get_verity_descriptor,
 380         .read_merkle_tree_page  = ext4_read_merkle_tree_page,
 381         .write_merkle_tree_block = ext4_write_merkle_tree_block,
 382 };