From 4a26620df451ad46151ad21d711ed43e963c004e Mon Sep 17 00:00:00 2001 From: Tyler Hicks Date: Sat, 5 Nov 2011 13:45:08 -0400 Subject: eCryptfs: Improve statfs reporting statfs() calls on eCryptfs files returned the wrong filesystem type and, when using filename encryption, the wrong maximum filename length. If mount-wide filename encryption is enabled, the cipher block size and the lower filesystem's max filename length will determine the max eCryptfs filename length. Pre-tested, known good lengths are used when the lower filesystem's namelen is 255 and a cipher with 8 or 16 byte block sizes is used. In other, less common cases, we fall back to a safe rounded-down estimate when determining the eCryptfs namelen. https://launchpad.net/bugs/885744 Signed-off-by: Tyler Hicks Reported-by: Kees Cook Reviewed-by: Kees Cook Reviewed-by: John Johansen --- fs/ecryptfs/crypto.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 61 insertions(+), 7 deletions(-) (limited to 'fs/ecryptfs/crypto.c') diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c index 63ab24510649..ea9931281557 100644 --- a/fs/ecryptfs/crypto.c +++ b/fs/ecryptfs/crypto.c @@ -1990,6 +1990,17 @@ out: return; } +static size_t ecryptfs_max_decoded_size(size_t encoded_size) +{ + /* Not exact; conservatively long. Every block of 4 + * encoded characters decodes into a block of 3 + * decoded characters. This segment of code provides + * the caller with the maximum amount of allocated + * space that @dst will need to point to in a + * subsequent call. */ + return ((encoded_size + 1) * 3) / 4; +} + /** * ecryptfs_decode_from_filename * @dst: If NULL, this function only sets @dst_size and returns. If @@ -2008,13 +2019,7 @@ ecryptfs_decode_from_filename(unsigned char *dst, size_t *dst_size, size_t dst_byte_offset = 0; if (dst == NULL) { - /* Not exact; conservatively long. Every block of 4 - * encoded characters decodes into a block of 3 - * decoded characters. This segment of code provides - * the caller with the maximum amount of allocated - * space that @dst will need to point to in a - * subsequent call. */ - (*dst_size) = (((src_size + 1) * 3) / 4); + (*dst_size) = ecryptfs_max_decoded_size(src_size); goto out; } while (src_byte_offset < src_size) { @@ -2239,3 +2244,52 @@ out_free: out: return rc; } + +#define ENC_NAME_MAX_BLOCKLEN_8_OR_16 143 + +int ecryptfs_set_f_namelen(long *namelen, long lower_namelen, + struct ecryptfs_mount_crypt_stat *mount_crypt_stat) +{ + struct blkcipher_desc desc; + struct mutex *tfm_mutex; + size_t cipher_blocksize; + int rc; + + if (!(mount_crypt_stat->flags & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES)) { + (*namelen) = lower_namelen; + return 0; + } + + rc = ecryptfs_get_tfm_and_mutex_for_cipher_name(&desc.tfm, &tfm_mutex, + mount_crypt_stat->global_default_fn_cipher_name); + if (unlikely(rc)) { + (*namelen) = 0; + return rc; + } + + mutex_lock(tfm_mutex); + cipher_blocksize = crypto_blkcipher_blocksize(desc.tfm); + mutex_unlock(tfm_mutex); + + /* Return an exact amount for the common cases */ + if (lower_namelen == NAME_MAX + && (cipher_blocksize == 8 || cipher_blocksize == 16)) { + (*namelen) = ENC_NAME_MAX_BLOCKLEN_8_OR_16; + return 0; + } + + /* Return a safe estimate for the uncommon cases */ + (*namelen) = lower_namelen; + (*namelen) -= ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE; + /* Since this is the max decoded size, subtract 1 "decoded block" len */ + (*namelen) = ecryptfs_max_decoded_size(*namelen) - 3; + (*namelen) -= ECRYPTFS_TAG_70_MAX_METADATA_SIZE; + (*namelen) -= ECRYPTFS_FILENAME_MIN_RANDOM_PREPEND_BYTES; + /* Worst case is that the filename is padded nearly a full block size */ + (*namelen) -= cipher_blocksize - 1; + + if ((*namelen) < 0) + (*namelen) = 0; + + return 0; +} -- cgit v1.2.2