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 <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>
diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index 63ab245..ea99312 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -1990,6 +1990,17 @@
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 @@
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:
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;
+}