Fix possible attacks against data confidentiality through LUKS2 online
reencryption extension crash recovery.
An attacker can modify on-disk metadata to simulate decryption in
progress with crashed (unfinished) reencryption step and persistently
decrypt part of the LUKS device.
This attack requires repeated physical access to the LUKS device but
no knowledge of user passphrases.
The decryption step is performed after a valid user activates
the device with a correct passphrase and modified metadata.
There are no visible warnings for the user that such recovery happened
(except using the luksDump command). The attack can also be reversed
afterward (simulating crashed encryption from a plaintext) with
possible modification of revealed plaintext.
The problem was caused by reusing a mechanism designed for actual
reencryption operation without reassessing the security impact for new
encryption and decryption operations. While the reencryption requires
calculating and verifying both key digests, no digest was needed to
initiate decryption recovery if the destination is plaintext (no
encryption key). Also, some metadata (like encryption cipher) is not
protected, and an attacker could change it. Note that LUKS2 protects
visible metadata only when a random change occurs. It does not protect
against intentional modification but such modification must not cause
a violation of data confidentiality.
The fix introduces additional digest protection of reencryption
metadata. The digest is calculated from known keys and critical
reencryption metadata. Now an attacker cannot create correct metadata
digest without knowledge of a passphrase for used keyslots.
For more details, see LUKS2 On-Disk Format Specification version 1.1.0.
LUKS2 encryption with data shift required remaining
data size (size remaining after substracting --reduce-data-size value)
to be at least --reduce-data-size. This was wrong. Remaining
data size restriction should be correctly at least single sector
(whatever sector size is selected or auto-detected).
LUKS2 code read the whole header to buffer to verify checksum,
so malloc is called on unvalidated input size parameter.
This can cause out of memory or unintentional device reads.
(Header validation will fail later anyway - the size is unsupported.)
Just do not allow too small and too big allocations here and fail quickly.
Fixes: #683.
The hotzone segment offset has to be altered
accordingly no matter the segment type.
Note for testing: This feature is currently
blocked in cli but it should be tested via
API tests anyway.
This reverts commit 367cb7a761
and retains original crypt_reencrypt() symbol marked as deprecated
in favour of new crypt_reencrypt_run(). This makes cryptsetup 2.4.0
release fully backward compatible.
crypt_activate_by_token functions did not respect LUKS2 keyslot
priorities. These calls were able to activate device via keyslot with
CRYPT_SLOT_PRIORITY_IGNORE even when token was set to
CRYPT_ANY_TOKEN. This commit changes the token based activation
so that keyslot with priority ignore is eligible for unlock only
when specific token is selected. Also when activating with token
set to CRYPT_ANY_TOKEN keyslots with higher priority take precedence
over keyslots with normal priority. Keyslot with priority ignore are
correctly ignored when token is CRYPT_ANY_TOKEN.
The deadlock is hypothetical since libcryptsetup applications
usualy terminates after error. The deadlock could only emerge
in case where single process handles multiple crypt contexts.
Search for token handlers in %{libdir}/cryptsetup directory
by default. Distros may change default location via
--with-luks2-external-tokens-path parameter during configuration.
Starting with GCC10 and LTO enabled, current symbols
versioning hack does not work anymore. This patch
reflects on that and should be compatible with older
compilers that does not support __attribute__((symver))
yet.
Inspired by following code:
https://github.com/linux-rdma/rdma-core/blob/master/util/symver.h
It does not make sense to upload volume keys in
kernel keyring if segment cipher is cipher_null.
The real volume_key is thrown away and replaced
with empty key anyway.
This bug enabled to create LUKS2 keyslots encrypted by
cipher_null when explicitely requested by user. LUKS2
was never meant to allow keyslot encryption with
cipher_null. cipher_null is meant for debug purposes
only as a segment cipher.
