Re: [ 026/180] eCryptfs: Improve statfs reporting

[Tyler Hicks]

On 2012-10-02 00:52:23, Willy Tarreau wrote:
> 2.6.32-longterm review patch.  If anyone has any objections, please let me know.

Hi - Please drop this patch. It incorrectly calculates f_namelen and I
haven't had a chance to fix it yet. When I get a fix ready, I'll forward
the corrected patch to stable@xxxxxx Thanks!

Tyler

> 
> ------------------
> 
> From: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
> 
> commit 4a26620df451ad46151ad21d711ed43e963c004e upstream.
> 
> BugLink: http://bugs.launchpad.net/bugs/885744
> 
> 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@xxxxxxxxxxxxx>
> Reported-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Reviewed-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> Acked-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
> Signed-off-by: Tim Gardner <tim.gardner@xxxxxxxxxxxxx>
> Signed-off-by: Willy Tarreau <w@xxxxxx>
> ---
>  fs/ecryptfs/crypto.c          |   68 ++++++++++++++++++++++++++++++++++++----
>  fs/ecryptfs/ecryptfs_kernel.h |   11 ++++++
>  fs/ecryptfs/keystore.c        |    9 ++---
>  fs/ecryptfs/super.c           |   18 ++++++++++-
>  4 files changed, 92 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
> index 7e164bb..7786bf6 100644
> --- a/fs/ecryptfs/crypto.c
> +++ b/fs/ecryptfs/crypto.c
> @@ -2039,6 +2039,17 @@ 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
> @@ -2057,13 +2068,7 @@ 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) {
> @@ -2289,3 +2294,52 @@ 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;
> +}
> diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
> index 9685315..4181136 100644
> --- a/fs/ecryptfs/ecryptfs_kernel.h
> +++ b/fs/ecryptfs/ecryptfs_kernel.h
> @@ -219,12 +219,21 @@ ecryptfs_get_key_payload_data(struct key *key)
>  					  * dentry name */
>  #define ECRYPTFS_TAG_73_PACKET_TYPE 0x49 /* FEK-encrypted filename as
>  					  * metadata */
> +#define ECRYPTFS_MIN_PKT_LEN_SIZE 1 /* Min size to specify packet length */
> +#define ECRYPTFS_MAX_PKT_LEN_SIZE 2 /* Pass at least this many bytes to
> +				     * ecryptfs_parse_packet_length() and
> +				     * ecryptfs_write_packet_length()
> +				     */
>  /* Constraint: ECRYPTFS_FILENAME_MIN_RANDOM_PREPEND_BYTES >=
>   * ECRYPTFS_MAX_IV_BYTES */
>  #define ECRYPTFS_FILENAME_MIN_RANDOM_PREPEND_BYTES 16
>  #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."
> @@ -762,6 +771,8 @@ 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);
>  
> diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
> index 8f1a525..4f1feeb 100644
> --- a/fs/ecryptfs/keystore.c
> +++ b/fs/ecryptfs/keystore.c
> @@ -548,10 +548,7 @@ 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;
> @@ -806,10 +803,10 @@ 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 1a037f7..557469a 100644
> --- a/fs/ecryptfs/super.c
> +++ b/fs/ecryptfs/super.c
> @@ -30,6 +30,8 @@
>  #include <linux/smp_lock.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;
> @@ -137,7 +139,21 @@ static void ecryptfs_put_super(struct super_block *sb)
>   */
>  static int ecryptfs_statfs(struct dentry *dentry, struct kstatfs *buf)
>  {
> -	return vfs_statfs(ecryptfs_dentry_to_lower(dentry), buf);
> +	struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry);
> +	int rc;
> +
> +	if (!lower_dentry->d_sb->s_op->statfs)
> +		return -ENOSYS;
> +
> +	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;
>  }
>  
>  /**
> -- 
> 1.7.2.1.45.g54fbc
> 
> 
>

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