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 maximum filename length will determine the
maximum eCryptfs filename length. Known good eCryptfs filename lengths
are returned in the common cases, while a safe estimate is performed
when an uncommon cipher block size or lower filename length is
encountered.
Signed-off-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
Reported-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
fs/ecryptfs/crypto.c | 70 ++++++++++++++++++++++++++++++++++++----
fs/ecryptfs/ecryptfs_kernel.h | 5 +++
fs/ecryptfs/keystore.c | 9 ++---
fs/ecryptfs/super.c | 14 +++++++-
4 files changed, 84 insertions(+), 14 deletions(-)
diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index 2a83425..76a7dce 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -2026,6 +2026,17 @@ 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
@@ -2044,13 +2055,7 @@ 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) {
@@ -2275,3 +2280,54 @@ out_free:
out:
return rc;
}
+
+#define ENC_NAME_MAX_BLOCKLEN_8 143
+#define ENC_NAME_MAX_BLOCKLEN_16 143
+
+int ecryptfs_set_f_namelen(size_t *namelen, size_t 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) {
+ if (cipher_blocksize == 8) {
+ (*namelen) = ENC_NAME_MAX_BLOCKLEN_8;
+ return 0;
+ } else if (cipher_blocksize == 16) {
+ (*namelen) = ENC_NAME_MAX_BLOCKLEN_16;
+ return 0;
+ }
+ }
+
+ /* Return a safe estimate for the uncommon cases */
+ (*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;
+
+ return 0;
+}
+
diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index a9f29b1..d8ab0b6 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -157,6 +157,9 @@ ecryptfs_get_key_payload_data(struct key *key)
#define ECRYPTFS_NON_NULL 0x42 /* A reasonable substitute for NULL */
#define MD5_DIGEST_SIZE 16
#define ECRYPTFS_TAG_70_DIGEST_SIZE MD5_DIGEST_SIZE
+#define ECRYPTFS_TAG_70_MIN_METADATA_SIZE (1 + 1 + ECRYPTFS_SIG_SIZE + 1 + 1)
+#define ECRYPTFS_TAG_70_MAX_METADATA_SIZE (ECRYPTFS_TAG_70_MIN_METADATA_SIZE \
+ + 1)
#define ECRYPTFS_FEK_ENCRYPTED_FILENAME_PREFIX "ECRYPTFS_FEK_ENCRYPTED."
#define ECRYPTFS_FEK_ENCRYPTED_FILENAME_PREFIX_SIZE 23
#define ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX "ECRYPTFS_FNEK_ENCRYPTED."
@@ -696,6 +699,8 @@ ecryptfs_parse_tag_70_packet(char **filename, size_t *filename_size,
size_t *packet_size,
struct ecryptfs_mount_crypt_stat *mount_crypt_stat,
char *data, size_t max_packet_size);
+int ecryptfs_set_f_namelen(size_t *namelen, size_t lower_namelen,
+ struct ecryptfs_mount_crypt_stat *mount_crypt_stat);
int ecryptfs_derive_iv(char *iv, struct ecryptfs_crypt_stat *crypt_stat,
loff_t offset);
diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index ac1ad48..06aab59 100644
--- a/fs/ecryptfs/keystore.c
+++ b/fs/ecryptfs/keystore.c
@@ -678,10 +678,7 @@ ecryptfs_write_tag_70_packet(char *dest, size_t *remaining_bytes,
* Octets N3-N4: Block-aligned encrypted filename
* - Consists of a minimum number of random characters, a \0
* separator, and then the filename */
- s->max_packet_size = (1 /* Tag 70 identifier */
- + 3 /* Max Tag 70 packet size */
- + ECRYPTFS_SIG_SIZE /* FNEK sig */
- + 1 /* Cipher identifier */
+ s->max_packet_size = (ECRYPTFS_TAG_70_MAX_METADATA_SIZE
+ s->block_aligned_filename_size);
if (dest == NULL) {
(*packet_size) = s->max_packet_size;
@@ -933,10 +930,10 @@ ecryptfs_parse_tag_70_packet(char **filename, size_t *filename_size,
goto out;
}
s->desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;
- if (max_packet_size < (1 + 1 + ECRYPTFS_SIG_SIZE + 1 + 1)) {
+ if (max_packet_size < ECRYPTFS_TAG_70_MIN_METADATA_SIZE) {
printk(KERN_WARNING "%s: max_packet_size is [%zd]; it must be "
"at least [%d]\n", __func__, max_packet_size,
- (1 + 1 + ECRYPTFS_SIG_SIZE + 1 + 1));
+ ECRYPTFS_TAG_70_MIN_METADATA_SIZE);
rc = -EINVAL;
goto out;
}
diff --git a/fs/ecryptfs/super.c b/fs/ecryptfs/super.c
index dbd52d40..a04d9ef 100644
--- a/fs/ecryptfs/super.c
+++ b/fs/ecryptfs/super.c
@@ -30,6 +30,8 @@
#include <linux/seq_file.h>
#include <linux/file.h>
#include <linux/crypto.h>
+#include <linux/statfs.h>
+#include <linux/magic.h>
#include "ecryptfs_kernel.h"
struct kmem_cache *ecryptfs_inode_info_cache;
@@ -103,10 +105,20 @@ static void ecryptfs_destroy_inode(struct inode *inode)
static int ecryptfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry);
+ int rc;
if (!lower_dentry->d_sb->s_op->statfs)
return -ENOSYS;
- return lower_dentry->d_sb->s_op->statfs(lower_dentry, buf);
+
+ rc = lower_dentry->d_sb->s_op->statfs(lower_dentry, buf);
+ if (rc)
+ return rc;
+
+ buf->f_type = ECRYPTFS_SUPER_MAGIC;
+ rc = ecryptfs_set_f_namelen(&buf->f_namelen, buf->f_namelen,
+ &ecryptfs_superblock_to_private(dentry->d_sb)->mount_crypt_stat);
+
+ return rc;
}
/**
--
1.7.5.4
--
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