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Commit fb4622ee authored by Eric Biggers's avatar Eric Biggers Committed by Lee Jones
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UPSTREAM: fscrypt: fix derivation of SipHash keys on big endian CPUs 

Typically, the cryptographic APIs that fscrypt uses take keys as byte
arrays, which avoids endianness issues.  However, siphash_key_t is an
exception.  It is defined as 'u64 key[2];', i.e. the 128-bit key is
expected to be given directly as two 64-bit words in CPU endianness.

fscrypt_derive_dirhash_key() and fscrypt_setup_iv_ino_lblk_32_key()
forgot to take this into account.  Therefore, the SipHash keys used to
index encrypted+casefolded directories differ on big endian vs. little
endian platforms, as do the SipHash keys used to hash inode numbers for
IV_INO_LBLK_32-encrypted directories.  This makes such directories
non-portable between these platforms.

Fix this by always using the little endian order.  This is a breaking
change for big endian platforms, but this should be fine in practice
since these features (encrypt+casefold support, and the IV_INO_LBLK_32
flag) aren't known to actually be used on any big endian platforms yet.

Bug: 254441685
Fixes: aa408f835d02 ("fscrypt: derive dirhash key for casefolded directories")
Fixes: e3b1078bedd3 ("fscrypt: add support for IV_INO_LBLK_32 policies")
Cc: <stable@vger.kernel.org> # v5.6+
Link: https://lore.kernel.org/r/20210605075033.54424-1-ebiggers@kernel.org


Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
(cherry picked from commit 2fc2b430f559fdf32d5d1dd5ceaa40e12fb77bdf)
Signed-off-by: default avatarLee Jones <joneslee@google.com>
Change-Id: I03555845a827b693fadaf1d61aa3977cd4ed9ecd
parent c8bc35f2

fs/crypto/keysetup.c

+32 −8
Original line number Diff line number Diff line
@@ -240,15 +240,40 @@ static int setup_per_mode_enc_key(struct fscrypt_info *ci, 
	return err;

}



/*

 * Derive a SipHash key from the given fscrypt master key and the given

 * application-specific information string.

 *

 * Note that the KDF produces a byte array, but the SipHash APIs expect the key

 * as a pair of 64-bit words.  Therefore, on big endian CPUs we have to do an

 * endianness swap in order to get the same results as on little endian CPUs.

 */

static int fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk,

				      u8 context, const u8 *info,

				      unsigned int infolen, siphash_key_t *key)

{

	int err;



	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,

				  (u8 *)key, sizeof(*key));

	if (err)

		return err;



	BUILD_BUG_ON(sizeof(*key) != 16);

	BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);

	le64_to_cpus(&key->key[0]);

	le64_to_cpus(&key->key[1]);

	return 0;

}



int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,

			       const struct fscrypt_master_key *mk)

{

	int err;



	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, HKDF_CONTEXT_DIRHASH_KEY,

	err = fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,

					 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,

				  (u8 *)&ci->ci_dirhash_key,

				  sizeof(ci->ci_dirhash_key));

					 &ci->ci_dirhash_key);

	if (err)

		return err;

	ci->ci_dirhash_key_initialized = true;
@@ -273,10 +298,9 @@ static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_info *ci, 
		if (mk->mk_ino_hash_key_initialized)

			goto unlock;



		err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,

					  HKDF_CONTEXT_INODE_HASH_KEY, NULL, 0,

					  (u8 *)&mk->mk_ino_hash_key,

					  sizeof(mk->mk_ino_hash_key));

		err = fscrypt_derive_siphash_key(mk,

						 HKDF_CONTEXT_INODE_HASH_KEY,

						 NULL, 0, &mk->mk_ino_hash_key);

		if (err)

			goto unlock;

		/* pairs with smp_load_acquire() above */