fs/f2fs/verity.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fs/f2fs/verity.c: fs-verity support for f2fs
   4  *
   5  * Copyright 2019 Google LLC
   6  */
   7
   8 /*
   9  * Implementation of fsverity_operations for f2fs.
  10  *
  11  * Like ext4, f2fs stores the verity metadata (Merkle tree and
  12  * fsverity_descriptor) past the end of the file, starting at the first 64K
  13  * boundary beyond i_size.  This approach works because (a) verity files are
  14  * readonly, and (b) pages fully beyond i_size aren't visible to userspace but
  15  * can be read/written internally by f2fs with only some relatively small
  16  * changes to f2fs.  Extended attributes cannot be used because (a) f2fs limits
  17  * the total size of an inode's xattr entries to 4096 bytes, which wouldn't be
  18  * enough for even a single Merkle tree block, and (b) f2fs encryption doesn't
  19  * encrypt xattrs, yet the verity metadata *must* be encrypted when the file is
  20  * because it contains hashes of the plaintext data.
  21  *
  22  * Using a 64K boundary rather than a 4K one keeps things ready for
  23  * architectures with 64K pages, and it doesn't necessarily waste space on-disk
  24  * since there can be a hole between i_size and the start of the Merkle tree.
  25  */
  26
  27 #include <linux/f2fs_fs.h>
  28
  29 #include "f2fs.h"
  30 #include "xattr.h"
  31
  32 #define F2FS_VERIFY_VER (1)
  33
  34 static inline loff_t f2fs_verity_metadata_pos(const struct inode *inode)
  35 {
  36         return round_up(inode->i_size, 65536);
  37 }
  38
  39 /*
  40  * Read some verity metadata from the inode.  __vfs_read() can't be used because
  41  * we need to read beyond i_size.
  42  */
  43 static int pagecache_read(struct inode *inode, void *buf, size_t count,
  44                           loff_t pos)
  45 {
  46         while (count) {
  47                 size_t n = min_t(size_t, count,
  48                                  PAGE_SIZE - offset_in_page(pos));
  49                 struct page *page;
  50
  51                 page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
  52                                          NULL);
  53                 if (IS_ERR(page))
  54                         return PTR_ERR(page);
  55
  56                 memcpy_from_page(buf, page, offset_in_page(pos), n);
  57
  58                 put_page(page);
  59
  60                 buf += n;
  61                 pos += n;
  62                 count -= n;
  63         }
  64         return 0;
  65 }
  66
  67 /*
  68  * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
  69  * kernel_write() can't be used because the file descriptor is readonly.
  70  */
  71 static int pagecache_write(struct inode *inode, const void *buf, size_t count,
  72                            loff_t pos)
  73 {
  74         struct address_space *mapping = inode->i_mapping;
  75         const struct address_space_operations *aops = mapping->a_ops;
  76
  77         if (pos + count > F2FS_BLK_TO_BYTES(max_file_blocks(inode)))
  78                 return -EFBIG;
  79
  80         while (count) {
  81                 size_t n = min_t(size_t, count,
  82                                  PAGE_SIZE - offset_in_page(pos));
  83                 struct folio *folio;
  84                 void *fsdata = NULL;
  85                 int res;
  86
  87                 res = aops->write_begin(NULL, mapping, pos, n, &folio, &fsdata);
  88                 if (res)
  89                         return res;
  90
  91                 memcpy_to_folio(folio, offset_in_folio(folio, pos), buf, n);
  92
  93                 res = aops->write_end(NULL, mapping, pos, n, n, folio, fsdata);
  94                 if (res < 0)
  95                         return res;
  96                 if (res != n)
  97                         return -EIO;
  98
  99                 buf += n;
 100                 pos += n;
 101                 count -= n;
 102         }
 103         return 0;
 104 }
 105
 106 /*
 107  * Format of f2fs verity xattr.  This points to the location of the verity
 108  * descriptor within the file data rather than containing it directly because
 109  * the verity descriptor *must* be encrypted when f2fs encryption is used.  But,
 110  * f2fs encryption does not encrypt xattrs.
 111  */
 112 struct fsverity_descriptor_location {
 113         __le32 version;
 114         __le32 size;
 115         __le64 pos;
 116 };
 117
 118 static int f2fs_begin_enable_verity(struct file *filp)
 119 {
 120         struct inode *inode = file_inode(filp);
 121         int err;
 122
 123         if (f2fs_verity_in_progress(inode))
 124                 return -EBUSY;
 125
 126         if (f2fs_is_atomic_file(inode))
 127                 return -EOPNOTSUPP;
 128
 129         /*
 130          * Since the file was opened readonly, we have to initialize the quotas
 131          * here and not rely on ->open() doing it.  This must be done before
 132          * evicting the inline data.
 133          */
 134         err = f2fs_dquot_initialize(inode);
 135         if (err)
 136                 return err;
 137
 138         err = f2fs_convert_inline_inode(inode);
 139         if (err)
 140                 return err;
 141
 142         set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 143         return 0;
 144 }
 145
 146 static int f2fs_end_enable_verity(struct file *filp, const void *desc,
 147                                   size_t desc_size, u64 merkle_tree_size)
 148 {
 149         struct inode *inode = file_inode(filp);
 150         struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 151         u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
 152         struct fsverity_descriptor_location dloc = {
 153                 .version = cpu_to_le32(F2FS_VERIFY_VER),
 154                 .size = cpu_to_le32(desc_size),
 155                 .pos = cpu_to_le64(desc_pos),
 156         };
 157         int err = 0, err2 = 0;
 158
 159         /*
 160          * If an error already occurred (which fs/verity/ signals by passing
 161          * desc == NULL), then only clean-up is needed.
 162          */
 163         if (desc == NULL)
 164                 goto cleanup;
 165
 166         /* Append the verity descriptor. */
 167         err = pagecache_write(inode, desc, desc_size, desc_pos);
 168         if (err)
 169                 goto cleanup;
 170
 171         /*
 172          * Write all pages (both data and verity metadata).  Note that this must
 173          * happen before clearing FI_VERITY_IN_PROGRESS; otherwise pages beyond
 174          * i_size won't be written properly.  For crash consistency, this also
 175          * must happen before the verity inode flag gets persisted.
 176          */
 177         err = filemap_write_and_wait(inode->i_mapping);
 178         if (err)
 179                 goto cleanup;
 180
 181         /* Set the verity xattr. */
 182         err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
 183                             F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
 184                             NULL, XATTR_CREATE);
 185         if (err)
 186                 goto cleanup;
 187
 188         /* Finally, set the verity inode flag. */
 189         file_set_verity(inode);
 190         f2fs_set_inode_flags(inode);
 191         f2fs_mark_inode_dirty_sync(inode, true);
 192
 193         clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 194         return 0;
 195
 196 cleanup:
 197         /*
 198          * Verity failed to be enabled, so clean up by truncating any verity
 199          * metadata that was written beyond i_size (both from cache and from
 200          * disk) and clearing FI_VERITY_IN_PROGRESS.
 201          *
 202          * Taking i_gc_rwsem[WRITE] is needed to stop f2fs garbage collection
 203          * from re-instantiating cached pages we are truncating (since unlike
 204          * normal file accesses, garbage collection isn't limited by i_size).
 205          */
 206         f2fs_down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 207         truncate_inode_pages(inode->i_mapping, inode->i_size);
 208         err2 = f2fs_truncate(inode);
 209         if (err2) {
 210                 f2fs_err(sbi, "Truncating verity metadata failed (errno=%d)",
 211                          err2);
 212                 set_sbi_flag(sbi, SBI_NEED_FSCK);
 213         }
 214         f2fs_up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 215         clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 216         return err ?: err2;
 217 }
 218
 219 static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
 220                                       size_t buf_size)
 221 {
 222         struct fsverity_descriptor_location dloc;
 223         int res;
 224         u32 size;
 225         u64 pos;
 226
 227         /* Get the descriptor location */
 228         res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
 229                             F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
 230         if (res < 0 && res != -ERANGE)
 231                 return res;
 232         if (res != sizeof(dloc) || dloc.version != cpu_to_le32(F2FS_VERIFY_VER)) {
 233                 f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
 234                 return -EINVAL;
 235         }
 236         size = le32_to_cpu(dloc.size);
 237         pos = le64_to_cpu(dloc.pos);
 238
 239         /* Get the descriptor */
 240         if (pos + size < pos ||
 241             pos + size > F2FS_BLK_TO_BYTES(max_file_blocks(inode)) ||
 242             pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
 243                 f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
 244                 f2fs_handle_error(F2FS_I_SB(inode),
 245                                 ERROR_CORRUPTED_VERITY_XATTR);
 246                 return -EFSCORRUPTED;
 247         }
 248         if (buf_size) {
 249                 if (size > buf_size)
 250                         return -ERANGE;
 251                 res = pagecache_read(inode, buf, size, pos);
 252                 if (res)
 253                         return res;
 254         }
 255         return size;
 256 }
 257
 258 static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
 259                                                pgoff_t index,
 260                                                unsigned long num_ra_pages)
 261 {
 262         struct folio *folio;
 263
 264         index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
 265
 266         folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
 267         if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
 268                 DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
 269
 270                 if (!IS_ERR(folio))
 271                         folio_put(folio);
 272                 else if (num_ra_pages > 1)
 273                         page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
 274                 folio = read_mapping_folio(inode->i_mapping, index, NULL);
 275                 if (IS_ERR(folio))
 276                         return ERR_CAST(folio);
 277         }
 278         return folio_file_page(folio, index);
 279 }
 280
 281 static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
 282                                         u64 pos, unsigned int size)
 283 {
 284         pos += f2fs_verity_metadata_pos(inode);
 285
 286         return pagecache_write(inode, buf, size, pos);
 287 }
 288
 289 const struct fsverity_operations f2fs_verityops = {
 290         .begin_enable_verity    = f2fs_begin_enable_verity,
 291         .end_enable_verity      = f2fs_end_enable_verity,
 292         .get_verity_descriptor  = f2fs_get_verity_descriptor,
 293         .read_merkle_tree_page  = f2fs_read_merkle_tree_page,
 294         .write_merkle_tree_block = f2fs_write_merkle_tree_block,
 295 };