LXR linux/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
  34static 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 */
  43static 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 */
  74static 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 */
 117struct fsverity_descriptor_location {
 118        __le32 version;
 119        __le32 size;
 120        __le64 pos;
 121};
 122
 123static 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
 151static 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        u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
 156        struct fsverity_descriptor_location dloc = {
 157                .version = cpu_to_le32(F2FS_VERIFY_VER),
 158                .size = cpu_to_le32(desc_size),
 159                .pos = cpu_to_le64(desc_pos),
 160        };
 161        int err = 0;
 162
 163        if (desc != NULL) {
 164                /* Succeeded; write the verity descriptor. */
 165                err = pagecache_write(inode, desc, desc_size, desc_pos);
 166
 167                /* Write all pages before clearing FI_VERITY_IN_PROGRESS. */
 168                if (!err)
 169                        err = filemap_write_and_wait(inode->i_mapping);
 170        }
 171
 172        /* If we failed, truncate anything we wrote past i_size. */
 173        if (desc == NULL || err)
 174                f2fs_truncate(inode);
 175
 176        clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
 177
 178        if (desc != NULL && !err) {
 179                err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
 180                                    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
 181                                    NULL, XATTR_CREATE);
 182                if (!err) {
 183                        file_set_verity(inode);
 184                        f2fs_set_inode_flags(inode);
 185                        f2fs_mark_inode_dirty_sync(inode, true);
 186                }
 187        }
 188        return err;
 189}
 190
 191static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
 192                                      size_t buf_size)
 193{
 194        struct fsverity_descriptor_location dloc;
 195        int res;
 196        u32 size;
 197        u64 pos;
 198
 199        /* Get the descriptor location */
 200        res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
 201                            F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
 202        if (res < 0 && res != -ERANGE)
 203                return res;
 204        if (res != sizeof(dloc) || dloc.version != cpu_to_le32(F2FS_VERIFY_VER)) {
 205                f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
 206                return -EINVAL;
 207        }
 208        size = le32_to_cpu(dloc.size);
 209        pos = le64_to_cpu(dloc.pos);
 210
 211        /* Get the descriptor */
 212        if (pos + size < pos || pos + size > inode->i_sb->s_maxbytes ||
 213            pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
 214                f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
 215                return -EFSCORRUPTED;
 216        }
 217        if (buf_size) {
 218                if (size > buf_size)
 219                        return -ERANGE;
 220                res = pagecache_read(inode, buf, size, pos);
 221                if (res)
 222                        return res;
 223        }
 224        return size;
 225}
 226
 227static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
 228                                               pgoff_t index,
 229                                               unsigned long num_ra_pages)
 230{
 231        DEFINE_READAHEAD(ractl, NULL, inode->i_mapping, index);
 232        struct page *page;
 233
 234        index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
 235
 236        page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
 237        if (!page || !PageUptodate(page)) {
 238                if (page)
 239                        put_page(page);
 240                else if (num_ra_pages > 1)
 241                        page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
 242                page = read_mapping_page(inode->i_mapping, index, NULL);
 243        }
 244        return page;
 245}
 246
 247static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
 248                                        u64 index, int log_blocksize)
 249{
 250        loff_t pos = f2fs_verity_metadata_pos(inode) + (index << log_blocksize);
 251
 252        return pagecache_write(inode, buf, 1 << log_blocksize, pos);
 253}
 254
 255const struct fsverity_operations f2fs_verityops = {
 256        .begin_enable_verity    = f2fs_begin_enable_verity,
 257        .end_enable_verity      = f2fs_end_enable_verity,
 258        .get_verity_descriptor  = f2fs_get_verity_descriptor,
 259        .read_merkle_tree_page  = f2fs_read_merkle_tree_page,
 260        .write_merkle_tree_block = f2fs_write_merkle_tree_block,
 261};
 262