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| author | Daniel Rosenberg | 2021-03-19 07:34:13 +0000 |
|---|---|---|
| committer | Theodore Ts'o | 2021-04-05 22:04:20 -0400 |
| commit | 471fbbea7ff7061b2d6474665cb5a2ceb4fd6500 (patch) | |
| tree | cd425ef9c0fcf3a5ebcdb5b5a81b2111a063ead0 /Documentation/filesystems | |
| parent | 400086d7c11327cfe1b1aa4487adceb41e82b4df (diff) | |
ext4: handle casefolding with encryption
This adds support for encryption with casefolding.
Since the name on disk is case preserving, and also encrypted, we can no
longer just recompute the hash on the fly. Additionally, to avoid
leaking extra information from the hash of the unencrypted name, we use
siphash via an fscrypt v2 policy.
The hash is stored at the end of the directory entry for all entries
inside of an encrypted and casefolded directory apart from those that
deal with '.' and '..'. This way, the change is backwards compatible
with existing ext4 filesystems.
[ Changed to advertise this feature via the file:
/sys/fs/ext4/features/encrypted_casefold -- TYT ]
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20210319073414.1381041-2-drosen@google.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/ext4/directory.rst | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/filesystems/ext4/directory.rst b/Documentation/filesystems/ext4/directory.rst index 073940cc64ed..55f618b37144 100644 --- a/Documentation/filesystems/ext4/directory.rst +++ b/Documentation/filesystems/ext4/directory.rst @@ -121,6 +121,31 @@ The directory file type is one of the following values: * - 0x7 - Symbolic link. +To support directories that are both encrypted and casefolded directories, we +must also include hash information in the directory entry. We append +``ext4_extended_dir_entry_2`` to ``ext4_dir_entry_2`` except for the entries +for dot and dotdot, which are kept the same. The structure follows immediately +after ``name`` and is included in the size listed by ``rec_len`` If a directory +entry uses this extension, it may be up to 271 bytes. + +.. list-table:: + :widths: 8 8 24 40 + :header-rows: 1 + + * - Offset + - Size + - Name + - Description + * - 0x0 + - \_\_le32 + - hash + - The hash of the directory name + * - 0x4 + - \_\_le32 + - minor\_hash + - The minor hash of the directory name + + In order to add checksums to these classic directory blocks, a phony ``struct ext4_dir_entry`` is placed at the end of each leaf block to hold the checksum. The directory entry is 12 bytes long. The inode @@ -322,6 +347,8 @@ The directory hash is one of the following values: - Half MD4, unsigned. * - 0x5 - Tea, unsigned. + * - 0x6 + - Siphash. Interior nodes of an htree are recorded as ``struct dx_node``, which is also the full length of a data block: |