From: Eric Biggers ebiggers@google.com

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() forgot to take this into account. Therefore, the SipHash keys used to index encrypted+casefolded directories differ on big endian vs. little endian platforms. 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 the encrypt+casefold support isn't known to actually be used on any big endian platforms yet.

Fixes: aa408f835d02 ("fscrypt: derive dirhash key for casefolded directories") Cc: stable@vger.kernel.org # v5.6+ Signed-off-by: Eric Biggers ebiggers@google.com --- fs/crypto/keysetup.c | 10 ++++++++++ 1 file changed, 10 insertions(+)

diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c index 261293fb7097..4d98377c07a7 100644 --- a/fs/crypto/keysetup.c +++ b/fs/crypto/keysetup.c @@ -221,6 +221,16 @@ int fscrypt_derive_dirhash_key(struct fscrypt_info *ci, sizeof(ci->ci_dirhash_key)); if (err) return err; + + /* + * The SipHash APIs expect the key as a pair of 64-bit words, not as a + * byte array. Make sure to use a consistent endianness. + */ + BUILD_BUG_ON(sizeof(ci->ci_dirhash_key) != 16); + BUILD_BUG_ON(ARRAY_SIZE(ci->ci_dirhash_key.key) != 2); + le64_to_cpus(&ci->ci_dirhash_key.key[0]); + le64_to_cpus(&ci->ci_dirhash_key.key[1]); + ci->ci_dirhash_key_initialized = true; return 0; }