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Commit 4a26620d authored by Tyler Hicks's avatar Tyler Hicks
Browse files

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: default avatarTyler Hicks <tyhicks@canonical.com>
Reported-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarJohn Johansen <john.johansen@canonical.com>
parent c38e2345

fs/ecryptfs/crypto.c

+61 −7
Original line number Diff line number Diff line
@@ -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;

}

fs/ecryptfs/ecryptfs_kernel.h

+6 −0
Original line number Diff line number Diff line
@@ -162,6 +162,10 @@ 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 + ECRYPTFS_MIN_PKT_LEN_SIZE \

					   + ECRYPTFS_SIG_SIZE + 1 + 1)

#define ECRYPTFS_TAG_70_MAX_METADATA_SIZE (1 + ECRYPTFS_MAX_PKT_LEN_SIZE \

					   + ECRYPTFS_SIG_SIZE + 1 + 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."
@@ -701,6 +705,8 @@ 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(long *namelen, long 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);

fs/ecryptfs/keystore.c

+3 −6
Original line number Diff line number Diff line
@@ -679,10 +679,7 @@ 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;
@@ -934,10 +931,10 @@ 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;

	}

fs/ecryptfs/super.c

+13 −1
Original line number Diff line number Diff line
@@ -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;
@@ -102,10 +104,20 @@ 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;

}



/**