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 static inline loff_t f2fs_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 /*
 110  * Format of f2fs verity xattr.  This points to the location of the verity
 111  * descriptor within the file data rather than containing it directly because
 112  * the verity descriptor *must* be encrypted when f2fs encryption is used.  But,
 113  * f2fs encryption does not encrypt xattrs.
 114  */
 115 struct fsverity_descriptor_location {
 116         __le32 version;
 117         __le32 size;
 118         __le64 pos;
 119 };
 120
 121 static int f2fs_begin_enable_verity(struct file *filp)
 122 {
 123         struct inode *inode = file_inode(filp);
 124         int err;
 125
 126         if (f2fs_verity_in_progress(inode))
 127                 return -EBUSY;
 128
 129         if (f2fs_is_atomic_file(inode) || f2fs_is_volatile_file(inode))
 130                 return -EOPNOTSUPP;
 131
 132         /*
 133          * Since the file was opened readonly, we have to initialize the quotas
 134          * here and not rely on ->open() doing it.  This must be done before
 135          * evicting the inline data.
 136          */
 137         err = dquot_initialize(inode);
 138         if (err)
 139                 return err;
 140
 141         err = f2fs_convert_inline_inode(inode);
 142         if (err)
 143                 return err;
 144
 145         set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 146         return 0;
 147 }
 148
 149 static int f2fs_end_enable_verity(struct file *filp, const void *desc,
 150                                   size_t desc_size, u64 merkle_tree_size)
 151 {
 152         struct inode *inode = file_inode(filp);
 153         u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
 154         struct fsverity_descriptor_location dloc = {
 155                 .version = cpu_to_le32(1),
 156                 .size = cpu_to_le32(desc_size),
 157                 .pos = cpu_to_le64(desc_pos),
 158         };
 159         int err = 0;
 160
 161         if (desc != NULL) {
 162                 /* Succeeded; write the verity descriptor. */
 163                 err = pagecache_write(inode, desc, desc_size, desc_pos);
 164
 165                 /* Write all pages before clearing FI_VERITY_IN_PROGRESS. */
 166                 if (!err)
 167                         err = filemap_write_and_wait(inode->i_mapping);
 168         }
 169
 170         /* If we failed, truncate anything we wrote past i_size. */
 171         if (desc == NULL || err)
 172                 f2fs_truncate(inode);
 173
 174         clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 175
 176         if (desc != NULL && !err) {
 177                 err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
 178                                     F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
 179                                     NULL, XATTR_CREATE);
 180                 if (!err) {
 181                         file_set_verity(inode);
 182                         f2fs_set_inode_flags(inode);
 183                         f2fs_mark_inode_dirty_sync(inode, true);
 184                 }
 185         }
 186         return err;
 187 }
 188
 189 static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
 190                                       size_t buf_size)
 191 {
 192         struct fsverity_descriptor_location dloc;
 193         int res;
 194         u32 size;
 195         u64 pos;
 196
 197         /* Get the descriptor location */
 198         res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
 199                             F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
 200         if (res < 0 && res != -ERANGE)
 201                 return res;
 202         if (res != sizeof(dloc) || dloc.version != cpu_to_le32(1)) {
 203                 f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
 204                 return -EINVAL;
 205         }
 206         size = le32_to_cpu(dloc.size);
 207         pos = le64_to_cpu(dloc.pos);
 208
 209         /* Get the descriptor */
 210         if (pos + size < pos || pos + size > inode->i_sb->s_maxbytes ||
 211             pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
 212                 f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
 213                 return -EFSCORRUPTED;
 214         }
 215         if (buf_size) {
 216                 if (size > buf_size)
 217                         return -ERANGE;
 218                 res = pagecache_read(inode, buf, size, pos);
 219                 if (res)
 220                         return res;
 221         }
 222         return size;
 223 }
 224
 225 static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
 226                                                pgoff_t index)
 227 {
 228         index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
 229
 230         return read_mapping_page(inode->i_mapping, index, NULL);
 231 }
 232
 233 static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
 234                                         u64 index, int log_blocksize)
 235 {
 236         loff_t pos = f2fs_verity_metadata_pos(inode) + (index << log_blocksize);
 237
 238         return pagecache_write(inode, buf, 1 << log_blocksize, pos);
 239 }
 240
 241 const struct fsverity_operations f2fs_verityops = {
 242         .begin_enable_verity    = f2fs_begin_enable_verity,
 243         .end_enable_verity      = f2fs_end_enable_verity,
 244         .get_verity_descriptor  = f2fs_get_verity_descriptor,
 245         .read_merkle_tree_page  = f2fs_read_merkle_tree_page,
 246         .write_merkle_tree_block = f2fs_write_merkle_tree_block,
 247 };