This patch adds support for Linux kernel (since version 5.11) dm-integrity
fixes that disables integrity recalculation if keyed algorithms (HMAC) is used.
Original dm-integrity superblock version <=4 is recalculation offset
field not protected by HMAC. An attacker can move this pointer and force
the kernel to recalculate the data area, ignoring original HMAC tags.
N.B. dm-integrity was not intended to protect against intentional changes.
Better use authenticated encryption (AEAD) in combination with dm-crypt.
It is designed to protect against random data corruption caused by hardware
or storage medium faults.
Despite that, we try to keep the system secure if keyed algorithms are used.
There are two possible keyed algorithms in dm-integrity - algorithm used
to protect journal and superblock (--journal-integrity) and algorithms
for protecting data (--integrity).
The dm-integrity superblock is guarded by --journal-integrity, so if you want
to protect data with HMAC, you should always also use HMAC for --journal-integrity.
The keys are independent. If HMAC is used for data but not for the journal,
recalculation is disabled by default.
For new kernel dm-integrity, the HMAC option also uses salt in superblock
to avoid an easy way to distinguish that the HMAC key is the same for two devices
(if data are the same).
The new HMAC and superblock are enabled automatically if the kernel supports it
(you can see superblock version 5 and fix_hmac flag in dump command).
If you need to use (insecure) backward compatibility, then two new integritysetup
options are introduced:
Use --integrity-legacy-recalc (instead of --integrity-recalc) to allow recalculation
on legacy devices.
Use --integrity-legacy-hmac in format action to force old insecure version
format (with HMAC).
Libcryptsetup API also introduces flags
CRYPT_COMPAT_LEGACY_INTEGRITY_HMAC and
CRYPT_COMPAT_LEGACY_INTEGRITY_RECALC
to set these through crypt_set_compatibility() call.
Some kernels show invalid dm-integrity table if suberblock
contains "recalculate" bit.
We can workaround that by setting recalculate option in table
(kernel uses bits from superblock anyway), so the table displayed
is always correct.
Fixes: #538
When integritysetup formats a device with hash or HMAC integrity checksums,
it requires explicitly tag size entry from a user (or default value).
This leads to confusion and shortened tags.
This patch calculates tag size according to real hash output, and
if tag size is specified, it warns if these values differ.
Fixes: #492.
The dump operation prints the fix_padding flag if set.
Also try to print warning if an old kernel is used and th edevice
cannot be activated because of missing fix padding support.
This patch adds support for fixed padding to cryptsetup.
* Cryptsetup will accept superblocks version 4.
* If the dm-integrity target version is greater than 1.4, cryptsetup will
add a flag "fix_padding" to the dm-integrity target arguments.
There is still one quirk: if we have an old libdm without
DM_DEVICE_GET_TARGET_VERSION and if dm-integrity module is not loaded,
cryptsetup will not detect that it can use the "fix_padding" option.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Support for multi-segment devices is requirement for online
reencryption to work. Introducing modififed dm backend that
splits data structures describing active device and individual
dm target (or segment).
Since the kernel 4.18 there is a possibility to speficy external
data device for dm-integrity that stores all integrity tags.
The new option --data-device in integritysetup uses this feature.
Some ciphers and key sizes created on-disk metadata that cannot be used.
Use the same test for length-preserving cipher as LUKS1.
Also check if key for integrity algorithm is not too small.
Fixes#373.
Kernel could reject HMAC without a key during format, we must set a key here as well.
Because there is no data area (device size is 8 sectors), it is actually never used,
so we can use zeroed key here.
The real HMAC key is used later during device activation with the real size.
The dm-integrity target is intended to be used for authenticated
encryption through LUKS and dm-crypt.
It can be used in standalone as well; for this use case there
is a simple configuration utility called integritysetup
(similar to veritysetup to dm-verity).
