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eCryptfs: Improve statfs reporting

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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 <tyhicks@canonical.com>
Reported-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: John Johansen <john.johansen@canonical.com>
This commit is contained in:
Tyler Hicks
2011-11-05 13:45:08 -04:00
parent c38e234562
commit 4a26620df4
4 changed files with 83 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

68
fs/ecryptfs/crypto.c
View File

@@ -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;
}