| Message ID | 20210527225525.2365513-1-ebiggers@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | fscrypt: fix derivation of SipHash keys on big endian CPUs | expand |
On Thu, May 27, 2021 at 03:55:25PM -0700, Eric Biggers wrote: > 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(+) I missed that fscrypt_setup_iv_ino_lblk_32_key() has the same bug too. I'll send out a new patch which fixes both of these... - Eric
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; }