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bitlk: implement validation of FVE metadata

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This commit implements FVE metadata block validation based on:
* CRC-32 (to detect random corruption);
* AES-CCM-encrypted SHA-256 (to detect malicious manipulations).

The hash-based validation requires us to decrypt the VMK first, so
it's only performed when obtaining the volume key.

This allows us to detect corrupted/altered FVE metadata blocks and
pick the valid one (before this commit: the first FVE metadata block
is always selected).

Fixes: #953

tests: add BitLocker image with corrupted headers

The image contains 2 manually corrupted metadata blocks (out of 3),
the library should use the third one to correctly load the volume.

Signed-off-by: Maxim Suhanov <dfirblog@gmail.com>
This commit is contained in:
Maxim Suhanov
2025-08-04 13:07:35 +03:00
committed by Milan Broz
parent 9cfdd6ba06
commit 68d4749d8a
3 changed files with 205 additions and 14 deletions
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11
lib/bitlk/bitlk.h
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@@ -21,6 +21,8 @@ struct volume_key;
#define BITLK_NONCE_SIZE 12
#define BITLK_SALT_SIZE 16
#define BITLK_VMK_MAC_TAG_SIZE 16
#define BITLK_VALIDATION_VMK_HEADER_SIZE 8
#define BITLK_VALIDATION_VMK_DATA_SIZE 72
#define BITLK_STATE_NORMAL 0x0004
@@ -85,6 +87,13 @@ struct bitlk_fvek {
struct volume_key *vk;
};
struct bitlk_validation {
uint8_t mac_tag[BITLK_VMK_MAC_TAG_SIZE];
uint8_t nonce[BITLK_NONCE_SIZE];
/* technically, this is not "VMK", but some sources call it this way */
uint8_t enc_datum[BITLK_VALIDATION_VMK_DATA_SIZE];
};
struct bitlk_metadata {
uint16_t sector_size;
uint64_t volume_size;
@@ -101,8 +110,10 @@ struct bitlk_metadata {
uint32_t metadata_version;
uint64_t volume_header_offset;
uint64_t volume_header_size;
const char *sha256_fve[32];
struct bitlk_vmk *vmks;
struct bitlk_fvek *fvek;
struct bitlk_validation *validation;
};
int BITLK_read_sb(struct crypt_device *cd, struct bitlk_metadata *params);