lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Date:   Sat,  5 Jun 2021 00:50:33 -0700
From:   Eric Biggers <>
        Daniel Rosenberg <>,
Subject: [PATCH v2] fscrypt: fix derivation of SipHash keys on big endian CPUs

From: Eric Biggers <>

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.

Fixes: aa408f835d02 ("fscrypt: derive dirhash key for casefolded directories")
Fixes: e3b1078bedd3 ("fscrypt: add support for IV_INO_LBLK_32 policies")
Cc: <> # v5.6+
Signed-off-by: Eric Biggers <>

v2: Fixed fscrypt_setup_iv_ino_lblk_32_key() too, not just

 fs/crypto/keysetup.c | 40 ++++++++++++++++++++++++++++++++--------
 1 file changed, 32 insertions(+), 8 deletions(-)

diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 261293fb70974..bca9c6658a7c5 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -210,15 +210,40 @@ 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,
-				  ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
-				  (u8 *)&ci->ci_dirhash_key,
-				  sizeof(ci->ci_dirhash_key));
+	err = fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
+					 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
+					 &ci->ci_dirhash_key);
 	if (err)
 		return err;
 	ci->ci_dirhash_key_initialized = true;
@@ -253,10 +278,9 @@ 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,
-					  (u8 *)&mk->mk_ino_hash_key,
-					  sizeof(mk->mk_ino_hash_key));
+		err = fscrypt_derive_siphash_key(mk,
+						 NULL, 0, &mk->mk_ino_hash_key);
 		if (err)
 			goto unlock;
 		/* pairs with smp_load_acquire() above */

base-commit: 77f30bfcfcf484da7208affd6a9e63406420bf91

Powered by blists - more mailing lists