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                 void *addr;
  51
  52                 page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
  53                                          NULL);
  54                 if (IS_ERR(page))
  55                         return PTR_ERR(page);
  56
  57                 addr = kmap_atomic(page);
  58                 memcpy(buf, addr + offset_in_page(pos), n);
  59                 kunmap_atomic(addr);
  60
  61                 put_page(page);
  62
  63                 buf += n;
  64                 pos += n;
  65                 count -= n;
  66         }
  67         return 0;
  68 }
  69
  70 /*
  71  * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
  72  * kernel_write() can't be used because the file descriptor is readonly.
  73  */
  74 static int pagecache_write(struct inode *inode, const void *buf, size_t count,
  75                            loff_t pos)
  76 {
  77         if (pos + count > inode->i_sb->s_maxbytes)
  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 page *page;
  84                 void *fsdata;
  85                 void *addr;
  86                 int res;
  87
  88                 res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
  89                                             &page, &fsdata);
  90                 if (res)
  91                         return res;
  92
  93                 addr = kmap_atomic(page);
  94                 memcpy(addr + offset_in_page(pos), buf, n);
  95                 kunmap_atomic(addr);
  96
  97                 res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
  98                                           page, fsdata);
  99                 if (res < 0)
 100                         return res;
 101                 if (res != n)
 102                         return -EIO;
 103
 104                 buf += n;
 105                 pos += n;
 106                 count -= n;
 107         }
 108         return 0;
 109 }
 110
 111 /*
 112  * Format of f2fs verity xattr.  This points to the location of the verity
 113  * descriptor within the file data rather than containing it directly because
 114  * the verity descriptor *must* be encrypted when f2fs encryption is used.  But,
 115  * f2fs encryption does not encrypt xattrs.
 116  */
 117 struct fsverity_descriptor_location {
 118         __le32 version;
 119         __le32 size;
 120         __le64 pos;
 121 };
 122
 123 static int f2fs_begin_enable_verity(struct file *filp)
 124 {
 125         struct inode *inode = file_inode(filp);
 126         int err;
 127
 128         if (f2fs_verity_in_progress(inode))
 129                 return -EBUSY;
 130
 131         if (f2fs_is_atomic_file(inode) || f2fs_is_volatile_file(inode))
 132                 return -EOPNOTSUPP;
 133
 134         /*
 135          * Since the file was opened readonly, we have to initialize the quotas
 136          * here and not rely on ->open() doing it.  This must be done before
 137          * evicting the inline data.
 138          */
 139         err = dquot_initialize(inode);
 140         if (err)
 141                 return err;
 142
 143         err = f2fs_convert_inline_inode(inode);
 144         if (err)
 145                 return err;
 146
 147         set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 148         return 0;
 149 }
 150
 151 static int f2fs_end_enable_verity(struct file *filp, const void *desc,
 152                                   size_t desc_size, u64 merkle_tree_size)
 153 {
 154         struct inode *inode = file_inode(filp);
 155         struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 156         u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
 157         struct fsverity_descriptor_location dloc = {
 158                 .version = cpu_to_le32(F2FS_VERIFY_VER),
 159                 .size = cpu_to_le32(desc_size),
 160                 .pos = cpu_to_le64(desc_pos),
 161         };
 162         int err = 0, err2 = 0;
 163
 164         /*
 165          * If an error already occurred (which fs/verity/ signals by passing
 166          * desc == NULL), then only clean-up is needed.
 167          */
 168         if (desc == NULL)
 169                 goto cleanup;
 170
 171         /* Append the verity descriptor. */
 172         err = pagecache_write(inode, desc, desc_size, desc_pos);
 173         if (err)
 174                 goto cleanup;
 175
 176         /*
 177          * Write all pages (both data and verity metadata).  Note that this must
 178          * happen before clearing FI_VERITY_IN_PROGRESS; otherwise pages beyond
 179          * i_size won't be written properly.  For crash consistency, this also
 180          * must happen before the verity inode flag gets persisted.
 181          */
 182         err = filemap_write_and_wait(inode->i_mapping);
 183         if (err)
 184                 goto cleanup;
 185
 186         /* Set the verity xattr. */
 187         err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
 188                             F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
 189                             NULL, XATTR_CREATE);
 190         if (err)
 191                 goto cleanup;
 192
 193         /* Finally, set the verity inode flag. */
 194         file_set_verity(inode);
 195         f2fs_set_inode_flags(inode);
 196         f2fs_mark_inode_dirty_sync(inode, true);
 197
 198         clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 199         return 0;
 200
 201 cleanup:
 202         /*
 203          * Verity failed to be enabled, so clean up by truncating any verity
 204          * metadata that was written beyond i_size (both from cache and from
 205          * disk) and clearing FI_VERITY_IN_PROGRESS.
 206          *
 207          * Taking i_gc_rwsem[WRITE] is needed to stop f2fs garbage collection
 208          * from re-instantiating cached pages we are truncating (since unlike
 209          * normal file accesses, garbage collection isn't limited by i_size).
 210          */
 211         down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 212         truncate_inode_pages(inode->i_mapping, inode->i_size);
 213         err2 = f2fs_truncate(inode);
 214         if (err2) {
 215                 f2fs_err(sbi, "Truncating verity metadata failed (errno=%d)",
 216                          err2);
 217                 set_sbi_flag(sbi, SBI_NEED_FSCK);
 218         }
 219         up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 220         clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 221         return err ?: err2;
 222 }
 223
 224 static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
 225                                       size_t buf_size)
 226 {
 227         struct fsverity_descriptor_location dloc;
 228         int res;
 229         u32 size;
 230         u64 pos;
 231
 232         /* Get the descriptor location */
 233         res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
 234                             F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
 235         if (res < 0 && res != -ERANGE)
 236                 return res;
 237         if (res != sizeof(dloc) || dloc.version != cpu_to_le32(F2FS_VERIFY_VER)) {
 238                 f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
 239                 return -EINVAL;
 240         }
 241         size = le32_to_cpu(dloc.size);
 242         pos = le64_to_cpu(dloc.pos);
 243
 244         /* Get the descriptor */
 245         if (pos + size < pos || pos + size > inode->i_sb->s_maxbytes ||
 246             pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
 247                 f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
 248                 return -EFSCORRUPTED;
 249         }
 250         if (buf_size) {
 251                 if (size > buf_size)
 252                         return -ERANGE;
 253                 res = pagecache_read(inode, buf, size, pos);
 254                 if (res)
 255                         return res;
 256         }
 257         return size;
 258 }
 259
 260 static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
 261                                                pgoff_t index,
 262                                                unsigned long num_ra_pages)
 263 {
 264         DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
 265         struct page *page;
 266
 267         index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
 268
 269         page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
 270         if (!page || !PageUptodate(page)) {
 271                 if (page)
 272                         put_page(page);
 273                 else if (num_ra_pages > 1)
 274                         page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
 275                 page = read_mapping_page(inode->i_mapping, index, NULL);
 276         }
 277         return page;
 278 }
 279
 280 static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
 281                                         u64 index, int log_blocksize)
 282 {
 283         loff_t pos = f2fs_verity_metadata_pos(inode) + (index << log_blocksize);
 284
 285         return pagecache_write(inode, buf, 1 << log_blocksize, pos);
 286 }
 287
 288 const struct fsverity_operations f2fs_verityops = {
 289         .begin_enable_verity    = f2fs_begin_enable_verity,
 290         .end_enable_verity      = f2fs_end_enable_verity,
 291         .get_verity_descriptor  = f2fs_get_verity_descriptor,
 292         .read_merkle_tree_page  = f2fs_read_merkle_tree_page,
 293         .write_merkle_tree_block = f2fs_write_merkle_tree_block,
 294 };