Add a function for filesystems to call to implement the
FS_IOC_ENABLE_VERITY ioctl. This ioctl enables fs-verity on a file.
See the "FS_IOC_ENABLE_VERITY" section of
Documentation/filesystems/fsverity.rst for the documentation.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add functions that verify data pages that have been read from a
fs-verity file, against that file's Merkle tree. These will be called
from filesystems' ->readpage() and ->readpages() methods.
Since data verification can block, a workqueue is provided for these
methods to enqueue verification work from their bio completion callback.
See the "Verifying data" section of
Documentation/filesystems/fsverity.rst for more information.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add a function fsverity_prepare_setattr() which filesystems that support
fs-verity must call to deny truncates of verity files.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add the fsverity_file_open() function, which prepares an fs-verity file
to be read from. If not already done, it loads the fs-verity descriptor
from the filesystem and sets up an fsverity_info structure for the inode
which describes the Merkle tree and contains the file measurement. It
also denies all attempts to open verity files for writing.
This commit also begins the include/linux/fsverity.h header, which
declares the interface between fs/verity/ and filesystems.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Analogous to fs/crypto/, add fields to the VFS inode and superblock for
use by the fs/verity/ support layer:
- ->s_vop: points to the fsverity_operations if the filesystem supports
fs-verity, otherwise is NULL.
- ->i_verity_info: points to cached fs-verity information for the inode
after someone opens it, otherwise is NULL.
- S_VERITY: bit in ->i_flags that identifies verity inodes, even when
they haven't been opened yet and thus still have NULL ->i_verity_info.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add the beginnings of the fs/verity/ support layer, including the
Kconfig option and various helper functions for hashing. To start, only
SHA-256 is supported, but other hash algorithms can easily be added.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add FS_VERITY_FL to the flags for FS_IOC_GETFLAGS, so that applications
can easily determine whether a file is a verity file at the same time as
they're checking other file flags. This flag will be gettable only;
FS_IOC_SETFLAGS won't allow setting it, since an ioctl must be used
instead to provide more parameters.
This flag matches the on-disk bit that was already allocated for ext4.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
fs-verity will be jointly maintained by Eric Biggers and Theodore Ts'o.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
If an directory has the a casefold flag set without the casefold
feature set, s_encoding will not be initialized, and this will cause
the kernel to dereference a NULL pointer. In addition to adding
checks to avoid these kernel oops, attempts to load inodes with the
casefold flag when the casefold feature is not enable will cause the
file system to be declared corrupted.
[Jaegeuk Kim: use EXT4_ERROR_INODE]
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Temporarily cache a casefolded version of the file name under lookup in
ext4_filename, to avoid repeatedly casefolding it. I got up to 30%
speedup on lookups of large directories (>100k entries), depending on
the length of the string under lookup.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Found by visual inspection, this wasn't caught by my xfstest, since it's
effect is ignoring positive dentries in the cache the fallback just goes
to the disk. it was introduced in the last iteration of the
case-insensitive patch.
d_compare should return 0 when the entries match, so make sure we are
correctly comparing the entire string if the encoding feature is set and
we are on a case-INsensitive directory.
Fixes: b886ee3e77 ("ext4: Support case-insensitive file name lookups")
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
scripts/mkutf8data is used only when regenerating utf8data.h,
which never happens in the normal kernel build. However, it is
irrespectively built if CONFIG_UNICODE is enabled.
Moreover, there is no good reason for it to reside in the scripts/
directory since it is only used in fs/unicode/.
Hence, move it from scripts/ to fs/unicode/.
In some cases, we bypass build artifacts in the normal build. The
conventional way to do so is to surround the code with ifdef REGENERATE_*.
For example,
- 7373f4f83c ("kbuild: add implicit rules for parser generation")
- 6aaf49b495 ("crypto: arm,arm64 - Fix random regeneration of S_shipped")
I rewrote the rule in a more kbuild'ish style.
In the normal build, utf8data.h is just shipped from the check-in file.
$ make
[ snip ]
SHIPPED fs/unicode/utf8data.h
CC fs/unicode/utf8-norm.o
CC fs/unicode/utf8-core.o
CC fs/unicode/utf8-selftest.o
AR fs/unicode/built-in.a
If you want to generate utf8data.h based on UCD, put *.txt files into
fs/unicode/, then pass REGENERATE_UTF8DATA=1 from the command line.
The mkutf8data tool will be automatically compiled to generate the
utf8data.h from the *.txt files.
$ make REGENERATE_UTF8DATA=1
[ snip ]
HOSTCC fs/unicode/mkutf8data
GEN fs/unicode/utf8data.h
CC fs/unicode/utf8-norm.o
CC fs/unicode/utf8-core.o
CC fs/unicode/utf8-selftest.o
AR fs/unicode/built-in.a
I renamed the check-in utf8data.h to utf8data.h_shipped so that this
will work for the out-of-tree build.
You can update it based on the latest UCD like this:
$ make REGENERATE_UTF8DATA=1 fs/unicode/
$ cp fs/unicode/utf8data.h fs/unicode/utf8data.h_shipped
Also, I added entries to .gitignore and dontdiff.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This patch implements the actual support for case-insensitive file name
lookups in ext4, based on the feature bit and the encoding stored in the
superblock.
A filesystem that has the casefold feature set is able to configure
directories with the +F (EXT4_CASEFOLD_FL) attribute, enabling lookups
to succeed in that directory in a case-insensitive fashion, i.e: match
a directory entry even if the name used by userspace is not a byte per
byte match with the disk name, but is an equivalent case-insensitive
version of the Unicode string. This operation is called a
case-insensitive file name lookup.
The feature is configured as an inode attribute applied to directories
and inherited by its children. This attribute can only be enabled on
empty directories for filesystems that support the encoding feature,
thus preventing collision of file names that only differ by case.
* dcache handling:
For a +F directory, Ext4 only stores the first equivalent name dentry
used in the dcache. This is done to prevent unintentional duplication of
dentries in the dcache, while also allowing the VFS code to quickly find
the right entry in the cache despite which equivalent string was used in
a previous lookup, without having to resort to ->lookup().
d_hash() of casefolded directories is implemented as the hash of the
casefolded string, such that we always have a well-known bucket for all
the equivalencies of the same string. d_compare() uses the
utf8_strncasecmp() infrastructure, which handles the comparison of
equivalent, same case, names as well.
For now, negative lookups are not inserted in the dcache, since they
would need to be invalidated anyway, because we can't trust missing file
dentries. This is bad for performance but requires some leveraging of
the vfs layer to fix. We can live without that for now, and so does
everyone else.
* on-disk data:
Despite using a specific version of the name as the internal
representation within the dcache, the name stored and fetched from the
disk is a byte-per-byte match with what the user requested, making this
implementation 'name-preserving'. i.e. no actual information is lost
when writing to storage.
DX is supported by modifying the hashes used in +F directories to make
them case/encoding-aware. The new disk hashes are calculated as the
hash of the full casefolded string, instead of the string directly.
This allows us to efficiently search for file names in the htree without
requiring the user to provide an exact name.
* Dealing with invalid sequences:
By default, when a invalid UTF-8 sequence is identified, ext4 will treat
it as an opaque byte sequence, ignoring the encoding and reverting to
the old behavior for that unique file. This means that case-insensitive
file name lookup will not work only for that file. An optional bit can
be set in the superblock telling the filesystem code and userspace tools
to enforce the encoding. When that optional bit is set, any attempt to
create a file name using an invalid UTF-8 sequence will fail and return
an error to userspace.
* Normalization algorithm:
The UTF-8 algorithms used to compare strings in ext4 is implemented
lives in fs/unicode, and is based on a previous version developed by
SGI. It implements the Canonical decomposition (NFD) algorithm
described by the Unicode specification 12.1, or higher, combined with
the elimination of ignorable code points (NFDi) and full
case-folding (CF) as documented in fs/unicode/utf8_norm.c.
NFD seems to be the best normalization method for EXT4 because:
- It has a lower cost than NFC/NFKC (which requires
decomposing to NFD as an intermediary step)
- It doesn't eliminate important semantic meaning like
compatibility decompositions.
Although:
- This implementation is not completely linguistic accurate, because
different languages have conflicting rules, which would require the
specialization of the filesystem to a given locale, which brings all
sorts of problems for removable media and for users who use more than
one language.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Support for encoding is considered an incompatible feature, since it has
potential to create collisions of file names in existing filesystems.
If the feature flag is not enabled, the entire filesystem will operate
on opaque byte sequences, respecting the original behavior.
The s_encoding field stores a magic number indicating the encoding
format and version used globally by file and directory names in the
filesystem. The s_encoding_flags defines policies for using the charset
encoding, like how to handle invalid sequences. The magic number is
mapped to the exact charset table, but the mapping is specific to ext4.
Since we don't have any commitment to support old encodings, the only
encoding I am supporting right now is utf8-12.1.0.
The current implementation prevents the user from enabling encoding and
per-directory encryption on the same filesystem at the same time. The
incompatibility between these features lies in how we do efficient
directory searches when we cannot be sure the encryption of the user
provided fname will match the actual hash stored in the disk without
decrypting every directory entry, because of normalization cases. My
quickest solution is to simply block the concurrent use of these
features for now, and enable it later, once we have a better solution.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Regenerate utf8data.h based on the latest UCD files and run tests
against the latest version.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This implements a in-kernel sanity test module for the utf8
normalization core. At probe time, it will run basic sequences through
the utf8n core, to identify problems will equivalent sequences and
normalization/casefold code. This is supposed to be useful for
regression testing when adding support for a new version of utf8 to
linux.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This patch integrates the utf8n patches with some higher level API to
perform UTF-8 string comparison, normalization and casefolding
operations. Implemented is a variation of NFD, and casefold is
performed by doing full casefold on top of NFD. These algorithms are
based on the core implemented by Olaf Weber from SGI.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Remove the Hangul decompositions from the utf8data trie, and do
algorithmic decomposition to calculate them on the fly. To store the
decomposition the caller of utf8lookup()/utf8nlookup() must provide a
12-byte buffer, which is used to synthesize a leaf with the
decomposition. This significantly reduces the size of the utf8data[]
array.
Changes made by Gabriel:
Rebase to mainline
Fix checkpatch errors
Extract robustness fixes and merge back to original mkutf8data.c patch
Regenerate utf8data.h
Signed-off-by: Olaf Weber <olaf@sgi.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Supporting functions for UTF-8 normalization are in utf8norm.c with the
header utf8norm.h. Two normalization forms are supported: nfdi and
nfdicf.
nfdi:
- Apply unicode normalization form NFD.
- Remove any Default_Ignorable_Code_Point.
nfdicf:
- Apply unicode normalization form NFD.
- Remove any Default_Ignorable_Code_Point.
- Apply a full casefold (C + F).
For the purposes of the code, a string is valid UTF-8 if:
- The values encoded are 0x1..0x10FFFF.
- The surrogate codepoints 0xD800..0xDFFFF are not encoded.
- The shortest possible encoding is used for all values.
The supporting functions work on null-terminated strings (utf8 prefix)
and on length-limited strings (utf8n prefix).
From the original SGI patch and for conformity with coding standards,
the utf8data_t typedef was dropped, since it was just masking the struct
keyword. On other occasions, namely utf8leaf_t and utf8trie_t, I
decided to keep it, since they are simple pointers to memory buffers,
and using uchars here wouldn't provide any more meaningful information.
From the original submission, we also converted from the compatibility
form to canonical.
Changes made by Gabriel:
Rebase to Mainline
Fix up checkpatch.pl warnings
Drop typedefs
move out of libxfs
Convert from NFKD to NFD
Signed-off-by: Olaf Weber <olaf@sgi.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
The decomposition and casefolding of UTF-8 characters are described in a
prefix tree in utf8data.h, which is a generate from the Unicode
Character Database (UCD), published by the Unicode Consortium, and
should not be edited by hand. The structures in utf8data.h are meant to
be used for lookup operations by the unicode subsystem, when decoding a
utf-8 string.
mkutf8data.c is the source for a program that generates utf8data.h. It
was written by Olaf Weber from SGI and originally proposed to be merged
into Linux in 2014. The original proposal performed the compatibility
decomposition, NFKD, but the current version was modified by me to do
canonical decomposition, NFD, as suggested by the community. The
changes from the original submission are:
* Rebase to mainline.
* Fix out-of-tree-build.
* Update makefile to build 11.0.0 ucd files.
* drop references to xfs.
* Convert NFKD to NFD.
* Merge back robustness fixes from original patch. Requested by
Dave Chinner.
The original submission is archived at:
<https://linux-xfs.oss.sgi.narkive.com/Xx10wjVY/rfc-unicode-utf-8-support-for-xfs>
The utf8data.h file can be regenerated using the instructions in
fs/unicode/README.utf8data.
- Notes on the update from 8.0.0 to 11.0:
The structure of the ucd files and special cases have not experienced
any changes between versions 8.0.0 and 11.0.0. 8.0.0 saw the addition
of Cherokee LC characters, which is an interesting case for
case-folding. The update is accompanied by new tests on the test_ucd
module to catch specific cases. No changes to mkutf8data script were
required for the updates.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
When getting fscrypt policy via EXT4_IOC_GET_ENCRYPTION_POLICY, if
encryption feature is off, it's better to return EOPNOTSUPP instead of
ENODATA, so let's add ext4_has_feature_encrypt() to do the check for
that.
This makes it so that all fscrypt ioctls consistently check for the
encryption feature, and makes ext4 consistent with f2fs in this regard.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
[EB - removed unneeded braces, updated the documentation, and
added more explanation to commit message]
Signed-off-by: Eric Biggers <ebiggers@google.com>
Update the fscrypt documentation file to catch up to all the latest
changes, including the new ioctls to manage master encryption keys in
the filesystem-level keyring and the support for v2 encryption policies.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Wire up the new ioctls for adding and removing fscrypt keys to/from the
filesystem, and the new ioctl for retrieving v2 encryption policies.
The key removal ioctls also required making UBIFS use
fscrypt_drop_inode().
For more details see Documentation/filesystems/fscrypt.rst and the
fscrypt patches that added the implementation of these ioctls.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Wire up the new ioctls for adding and removing fscrypt keys to/from the
filesystem, and the new ioctl for retrieving v2 encryption policies.
The key removal ioctls also required making f2fs_drop_inode() call
fscrypt_drop_inode().
For more details see Documentation/filesystems/fscrypt.rst and the
fscrypt patches that added the implementation of these ioctls.
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Wire up the new ioctls for adding and removing fscrypt keys to/from the
filesystem, and the new ioctl for retrieving v2 encryption policies.
The key removal ioctls also required making ext4_drop_inode() call
fscrypt_drop_inode().
For more details see Documentation/filesystems/fscrypt.rst and the
fscrypt patches that added the implementation of these ioctls.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
By looking up the master keys in a filesystem-level keyring rather than
in the calling processes' key hierarchy, it becomes possible for a user
to set an encryption policy which refers to some key they don't actually
know, then encrypt their files using that key. Cryptographically this
isn't much of a problem, but the semantics of this would be a bit weird.
Thus, enforce that a v2 encryption policy can only be set if the user
has previously added the key, or has capable(CAP_FOWNER).
We tolerate that this problem will continue to exist for v1 encryption
policies, however; there is no way around that.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add a root-only variant of the FS_IOC_REMOVE_ENCRYPTION_KEY ioctl which
removes all users' claims of the key, not just the current user's claim.
I.e., it always removes the key itself, no matter how many users have
added it.
This is useful for forcing a directory to be locked, without having to
figure out which user ID(s) the key was added under. This is planned to
be used by a command like 'sudo fscrypt lock DIR --all-users' in the
fscrypt userspace tool (http://github.com/google/fscrypt).
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Allow the FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY
ioctls to be used by non-root users to add and remove encryption keys
from the filesystem-level crypto keyrings, subject to limitations.
Motivation: while privileged fscrypt key management is sufficient for
some users (e.g. Android and Chromium OS, where a privileged process
manages all keys), the old API by design also allows non-root users to
set up and use encrypted directories, and we don't want to regress on
that. Especially, we don't want to force users to continue using the
old API, running into the visibility mismatch between files and keyrings
and being unable to "lock" encrypted directories.
Intuitively, the ioctls have to be privileged since they manipulate
filesystem-level state. However, it's actually safe to make them
unprivileged if we very carefully enforce some specific limitations.
First, each key must be identified by a cryptographic hash so that a
user can't add the wrong key for another user's files. For v2
encryption policies, we use the key_identifier for this. v1 policies
don't have this, so managing keys for them remains privileged.
Second, each key a user adds is charged to their quota for the keyrings
service. Thus, a user can't exhaust memory by adding a huge number of
keys. By default each non-root user is allowed up to 200 keys; this can
be changed using the existing sysctl 'kernel.keys.maxkeys'.
Third, if multiple users add the same key, we keep track of those users
of the key (of which there remains a single copy), and won't really
remove the key, i.e. "lock" the encrypted files, until all those users
have removed it. This prevents denial of service attacks that would be
possible under simpler schemes, such allowing the first user who added a
key to remove it -- since that could be a malicious user who has
compromised the key. Of course, encryption keys should be kept secret,
but the idea is that using encryption should never be *less* secure than
not using encryption, even if your key was compromised.
We tolerate that a user will be unable to really remove a key, i.e.
unable to "lock" their encrypted files, if another user has added the
same key. But in a sense, this is actually a good thing because it will
avoid providing a false notion of security where a key appears to have
been removed when actually it's still in memory, available to any
attacker who compromises the operating system kernel.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add a new fscrypt policy version, "v2". It has the following changes
from the original policy version, which we call "v1" (*):
- Master keys (the user-provided encryption keys) are only ever used as
input to HKDF-SHA512. This is more flexible and less error-prone, and
it avoids the quirks and limitations of the AES-128-ECB based KDF.
Three classes of cryptographically isolated subkeys are defined:
- Per-file keys, like used in v1 policies except for the new KDF.
- Per-mode keys. These implement the semantics of the DIRECT_KEY
flag, which for v1 policies made the master key be used directly.
These are also planned to be used for inline encryption when
support for it is added.
- Key identifiers (see below).
- Each master key is identified by a 16-byte master_key_identifier,
which is derived from the key itself using HKDF-SHA512. This prevents
users from associating the wrong key with an encrypted file or
directory. This was easily possible with v1 policies, which
identified the key by an arbitrary 8-byte master_key_descriptor.
- The key must be provided in the filesystem-level keyring, not in a
process-subscribed keyring.
The following UAPI additions are made:
- The existing ioctl FS_IOC_SET_ENCRYPTION_POLICY can now be passed a
fscrypt_policy_v2 to set a v2 encryption policy. It's disambiguated
from fscrypt_policy/fscrypt_policy_v1 by the version code prefix.
- A new ioctl FS_IOC_GET_ENCRYPTION_POLICY_EX is added. It allows
getting the v1 or v2 encryption policy of an encrypted file or
directory. The existing FS_IOC_GET_ENCRYPTION_POLICY ioctl could not
be used because it did not have a way for userspace to indicate which
policy structure is expected. The new ioctl includes a size field, so
it is extensible to future fscrypt policy versions.
- The ioctls FS_IOC_ADD_ENCRYPTION_KEY, FS_IOC_REMOVE_ENCRYPTION_KEY,
and FS_IOC_GET_ENCRYPTION_KEY_STATUS now support managing keys for v2
encryption policies. Such keys are kept logically separate from keys
for v1 encryption policies, and are identified by 'identifier' rather
than by 'descriptor'. The 'identifier' need not be provided when
adding a key, since the kernel will calculate it anyway.
This patch temporarily keeps adding/removing v2 policy keys behind the
same permission check done for adding/removing v1 policy keys:
capable(CAP_SYS_ADMIN). However, the next patch will carefully take
advantage of the cryptographically secure master_key_identifier to allow
non-root users to add/remove v2 policy keys, thus providing a full
replacement for v1 policies.
(*) Actually, in the API fscrypt_policy::version is 0 while on-disk
fscrypt_context::format is 1. But I believe it makes the most sense
to advance both to '2' to have them be in sync, and to consider the
numbering to start at 1 except for the API quirk.
Reviewed-by: Paul Crowley <paulcrowley@google.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add an implementation of HKDF (RFC 5869) to fscrypt, for the purpose of
deriving additional key material from the fscrypt master keys for v2
encryption policies. HKDF is a key derivation function built on top of
HMAC. We choose SHA-512 for the underlying unkeyed hash, and use an
"hmac(sha512)" transform allocated from the crypto API.
We'll be using this to replace the AES-ECB based KDF currently used to
derive the per-file encryption keys. While the AES-ECB based KDF is
believed to meet the original security requirements, it is nonstandard
and has problems that don't exist in modern KDFs such as HKDF:
1. It's reversible. Given a derived key and nonce, an attacker can
easily compute the master key. This is okay if the master key and
derived keys are equally hard to compromise, but now we'd like to be
more robust against threats such as a derived key being compromised
through a timing attack, or a derived key for an in-use file being
compromised after the master key has already been removed.
2. It doesn't evenly distribute the entropy from the master key; each 16
input bytes only affects the corresponding 16 output bytes.
3. It isn't easily extensible to deriving other values or keys, such as
a public hash for securely identifying the key, or per-mode keys.
Per-mode keys will be immediately useful for Adiantum encryption, for
which fscrypt currently uses the master key directly, introducing
unnecessary usage constraints. Per-mode keys will also be useful for
hardware inline encryption, which is currently being worked on.
HKDF solves all the above problems.
Reviewed-by: Paul Crowley <paulcrowley@google.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add a new fscrypt ioctl, FS_IOC_GET_ENCRYPTION_KEY_STATUS. Given a key
specified by 'struct fscrypt_key_specifier' (the same way a key is
specified for the other fscrypt key management ioctls), it returns
status information in a 'struct fscrypt_get_key_status_arg'.
The main motivation for this is that applications need to be able to
check whether an encrypted directory is "unlocked" or not, so that they
can add the key if it is not, and avoid adding the key (which may
involve prompting the user for a passphrase) if it already is.
It's possible to use some workarounds such as checking whether opening a
regular file fails with ENOKEY, or checking whether the filenames "look
like gibberish" or not. However, no workaround is usable in all cases.
Like the other key management ioctls, the keyrings syscalls may seem at
first to be a good fit for this. Unfortunately, they are not. Even if
we exposed the keyring ID of the ->s_master_keys keyring and gave
everyone Search permission on it (note: currently the keyrings
permission system would also allow everyone to "invalidate" the keyring
too), the fscrypt keys have an additional state that doesn't map cleanly
to the keyrings API: the secret can be removed, but we can be still
tracking the files that were using the key, and the removal can be
re-attempted or the secret added again.
After later patches, some applications will also need a way to determine
whether a key was added by the current user vs. by some other user.
Reserved fields are included in fscrypt_get_key_status_arg for this and
other future extensions.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add a new fscrypt ioctl, FS_IOC_REMOVE_ENCRYPTION_KEY. This ioctl
removes an encryption key that was added by FS_IOC_ADD_ENCRYPTION_KEY.
It wipes the secret key itself, then "locks" the encrypted files and
directories that had been unlocked using that key -- implemented by
evicting the relevant dentries and inodes from the VFS caches.
The problem this solves is that many fscrypt users want the ability to
remove encryption keys, causing the corresponding encrypted directories
to appear "locked" (presented in ciphertext form) again. Moreover,
users want removing an encryption key to *really* remove it, in the
sense that the removed keys cannot be recovered even if kernel memory is
compromised, e.g. by the exploit of a kernel security vulnerability or
by a physical attack. This is desirable after a user logs out of the
system, for example. In many cases users even already assume this to be
the case and are surprised to hear when it's not.
It is not sufficient to simply unlink the master key from the keyring
(or to revoke or invalidate it), since the actual encryption transform
objects are still pinned in memory by their inodes. Therefore, to
really remove a key we must also evict the relevant inodes.
Currently one workaround is to run 'sync && echo 2 >
/proc/sys/vm/drop_caches'. But, that evicts all unused inodes in the
system rather than just the inodes associated with the key being
removed, causing severe performance problems. Moreover, it requires
root privileges, so regular users can't "lock" their encrypted files.
Another workaround, used in Chromium OS kernels, is to add a new
VFS-level ioctl FS_IOC_DROP_CACHE which is a more restricted version of
drop_caches that operates on a single super_block. It does:
shrink_dcache_sb(sb);
invalidate_inodes(sb, false);
But it's still a hack. Yet, the major users of filesystem encryption
want this feature badly enough that they are actually using these hacks.
To properly solve the problem, start maintaining a list of the inodes
which have been "unlocked" using each master key. Originally this
wasn't possible because the kernel didn't keep track of in-use master
keys at all. But, with the ->s_master_keys keyring it is now possible.
Then, add an ioctl FS_IOC_REMOVE_ENCRYPTION_KEY. It finds the specified
master key in ->s_master_keys, then wipes the secret key itself, which
prevents any additional inodes from being unlocked with the key. Then,
it syncs the filesystem and evicts the inodes in the key's list. The
normal inode eviction code will free and wipe the per-file keys (in
->i_crypt_info). Note that freeing ->i_crypt_info without evicting the
inodes was also considered, but would have been racy.
Some inodes may still be in use when a master key is removed, and we
can't simply revoke random file descriptors, mmap's, etc. Thus, the
ioctl simply skips in-use inodes, and returns -EBUSY to indicate that
some inodes weren't evicted. The master key *secret* is still removed,
but the fscrypt_master_key struct remains to keep track of the remaining
inodes. Userspace can then retry the ioctl to evict the remaining
inodes. Alternatively, if userspace adds the key again, the refreshed
secret will be associated with the existing list of inodes so they
remain correctly tracked for future key removals.
The ioctl doesn't wipe pagecache pages. Thus, we tolerate that after a
kernel compromise some portions of plaintext file contents may still be
recoverable from memory. This can be solved by enabling page poisoning
system-wide, which security conscious users may choose to do. But it's
very difficult to solve otherwise, e.g. note that plaintext file
contents may have been read in other places than pagecache pages.
Like FS_IOC_ADD_ENCRYPTION_KEY, FS_IOC_REMOVE_ENCRYPTION_KEY is
initially restricted to privileged users only. This is sufficient for
some use cases, but not all. A later patch will relax this restriction,
but it will require introducing key hashes, among other changes.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add a new fscrypt ioctl, FS_IOC_ADD_ENCRYPTION_KEY. This ioctl adds an
encryption key to the filesystem's fscrypt keyring ->s_master_keys,
making any files encrypted with that key appear "unlocked".
Why we need this
~~~~~~~~~~~~~~~~
The main problem is that the "locked/unlocked" (ciphertext/plaintext)
status of encrypted files is global, but the fscrypt keys are not.
fscrypt only looks for keys in the keyring(s) the process accessing the
filesystem is subscribed to: the thread keyring, process keyring, and
session keyring, where the session keyring may contain the user keyring.
Therefore, userspace has to put fscrypt keys in the keyrings for
individual users or sessions. But this means that when a process with a
different keyring tries to access encrypted files, whether they appear
"unlocked" or not is nondeterministic. This is because it depends on
whether the files are currently present in the inode cache.
Fixing this by consistently providing each process its own view of the
filesystem depending on whether it has the key or not isn't feasible due
to how the VFS caches work. Furthermore, while sometimes users expect
this behavior, it is misguided for two reasons. First, it would be an
OS-level access control mechanism largely redundant with existing access
control mechanisms such as UNIX file permissions, ACLs, LSMs, etc.
Encryption is actually for protecting the data at rest.
Second, almost all users of fscrypt actually do need the keys to be
global. The largest users of fscrypt, Android and Chromium OS, achieve
this by having PID 1 create a "session keyring" that is inherited by
every process. This works, but it isn't scalable because it prevents
session keyrings from being used for any other purpose.
On general-purpose Linux distros, the 'fscrypt' userspace tool [1] can't
similarly abuse the session keyring, so to make 'sudo' work on all
systems it has to link all the user keyrings into root's user keyring
[2]. This is ugly and raises security concerns. Moreover it can't make
the keys available to system services, such as sshd trying to access the
user's '~/.ssh' directory (see [3], [4]) or NetworkManager trying to
read certificates from the user's home directory (see [5]); or to Docker
containers (see [6], [7]).
By having an API to add a key to the *filesystem* we'll be able to fix
the above bugs, remove userspace workarounds, and clearly express the
intended semantics: the locked/unlocked status of an encrypted directory
is global, and encryption is orthogonal to OS-level access control.
Why not use the add_key() syscall
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We use an ioctl for this API rather than the existing add_key() system
call because the ioctl gives us the flexibility needed to implement
fscrypt-specific semantics that will be introduced in later patches:
- Supporting key removal with the semantics such that the secret is
removed immediately and any unused inodes using the key are evicted;
also, the eviction of any in-use inodes can be retried.
- Calculating a key-dependent cryptographic identifier and returning it
to userspace.
- Allowing keys to be added and removed by non-root users, but only keys
for v2 encryption policies; and to prevent denial-of-service attacks,
users can only remove keys they themselves have added, and a key is
only really removed after all users who added it have removed it.
Trying to shoehorn these semantics into the keyrings syscalls would be
very difficult, whereas the ioctls make things much easier.
However, to reuse code the implementation still uses the keyrings
service internally. Thus we get lockless RCU-mode key lookups without
having to re-implement it, and the keys automatically show up in
/proc/keys for debugging purposes.
References:
[1] https://github.com/google/fscrypt
[2] https://goo.gl/55cCrI#heading=h.vf09isp98isb
[3] https://github.com/google/fscrypt/issues/111#issuecomment-444347939
[4] https://github.com/google/fscrypt/issues/116
[5] https://bugs.launchpad.net/ubuntu/+source/fscrypt/+bug/1770715
[6] https://github.com/google/fscrypt/issues/128
[7] https://askubuntu.com/questions/1130306/cannot-run-docker-on-an-encrypted-filesystem
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Rename keyinfo.c to keysetup.c since this better describes what the file
does (sets up the key), and it matches the new file keysetup_v1.c.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
In preparation for introducing v2 encryption policies which will find
and derive encryption keys differently from the current v1 encryption
policies, move the v1 policy-specific key setup code from keyinfo.c into
keysetup_v1.c.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Do some more refactoring of the key setup code, in preparation for
introducing a filesystem-level keyring and v2 encryption policies:
- Now that ci_inode exists, don't pass around the inode unnecessarily.
- Define a function setup_file_encryption_key() which handles the crypto
key setup given an under-construction fscrypt_info. Don't pass the
fscrypt_context, since everything is in the fscrypt_info.
[This will be extended for v2 policies and the fs-level keyring.]
- Define a function fscrypt_set_derived_key() which sets the per-file
key, without depending on anything specific to v1 policies.
[This will also be used for v2 policies.]
- Define a function fscrypt_setup_v1_file_key() which takes the raw
master key, thus separating finding the key from using it.
[This will also be used if the key is found in the fs-level keyring.]
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
In preparation for introducing a filesystem-level keyring which will
contain fscrypt master keys, rename the existing 'struct
fscrypt_master_key' to 'struct fscrypt_direct_key'. This is the
structure in the existing table of master keys that's maintained to
deduplicate the crypto transforms for v1 DIRECT_KEY policies.
I've chosen to keep this table as-is rather than make it automagically
add/remove the keys to/from the filesystem-level keyring, since that
would add a lot of extra complexity to the filesystem-level keyring.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Add an inode back-pointer to 'struct fscrypt_info', such that
inode->i_crypt_info->ci_inode == inode.
This will be useful for:
1. Evicting the inodes when a fscrypt key is removed, since we'll track
the inodes using a given key by linking their fscrypt_infos together,
rather than the inodes directly. This avoids bloating 'struct inode'
with a new list_head.
2. Simplifying the per-file key setup, since the inode pointer won't
have to be passed around everywhere just in case something goes wrong
and it's needed for fscrypt_warn().
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Update fs/crypto/ to use the new names for the UAPI constants rather
than the old names, then make the old definitions conditional on
!__KERNEL__.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Prefix all filesystem encryption UAPI constants except the ioctl numbers
with "FSCRYPT_" rather than with "FS_". This namespaces the constants
more appropriately and makes it clear that they are related specifically
to the filesystem encryption feature, and to the 'fscrypt_*' structures.
With some of the old names like "FS_POLICY_FLAGS_VALID", it was not
immediately clear that the constant had anything to do with encryption.
This is also useful because we'll be adding more encryption-related
constants, e.g. for the policy version, and we'd otherwise have to
choose whether to use unclear names like FS_POLICY_V1 or inconsistent
names like FS_ENCRYPTION_POLICY_V1.
For source compatibility with existing userspace programs, keep the old
names defined as aliases to the new names.
Finally, as long as new names are being defined anyway, I skipped
defining new names for the fscrypt mode numbers that aren't actually
used: INVALID (0), AES_256_GCM (2), AES_256_CBC (3), SPECK128_256_XTS
(7), and SPECK128_256_CTS (8).
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
More fscrypt definitions are being added, and we shouldn't use a
disproportionate amount of space in <linux/fs.h> for fscrypt stuff.
So move the fscrypt definitions to a new header <linux/fscrypt.h>.
For source compatibility with existing userspace programs, <linux/fs.h>
still includes the new header.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Return ENOPKG rather than ENOENT when trying to open a file that's
encrypted using algorithms not available in the kernel's crypto API.
This avoids an ambiguity, since ENOENT is also returned when the file
doesn't exist.
Note: this is the same approach I'm taking for fs-verity.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Users of fscrypt with non-default algorithms will encounter an error
like the following if they fail to include the needed algorithms into
the crypto API when configuring the kernel (as per the documentation):
Error allocating 'adiantum(xchacha12,aes)' transform: -2
This requires that the user figure out what the "-2" error means.
Make it more friendly by printing a warning like the following instead:
Missing crypto API support for Adiantum (API name: "adiantum(xchacha12,aes)")
Also upgrade the log level for *other* errors to KERN_ERR.
Signed-off-by: Eric Biggers <ebiggers@google.com>
When fs/crypto/ encounters an inode with an invalid encryption context,
currently it prints a warning if the pair of encryption modes are
unrecognized, but it's silent if there are other problems such as
unsupported context size, format, or flags. To help people debug such
situations, add more warning messages.
Signed-off-by: Eric Biggers <ebiggers@google.com>
