Re: [PATCH] ecryptfs: Fix stat command displays wrong file size in xattr region

[Tyler Hicks]

Hi Jason! My apologies for not getting to this review earlier. I haven't
had much time to spend on eCryptfs lately.

Thanks for this bug fix! This patch looks mostly good but I have a
suggestion and question below.

On 06/22/2017 02:21 AM, Jason Xing wrote:
> When doing ecryptfs_read_and_validate_xattr_region(), eCryptfs
> reads only 16 bytes from xattr region. However, the lower filesystem
> like ext4 always compares 16 with the size of ecryptfs xattr region
> which is 81 bytes, and then it will return ERANGE (-34) and do not
> read that region.
> 
> Signed-off-by: Jason Xing <kerneljasonxing@xxxxxxxxx>
> ---
>  fs/ecryptfs/crypto.c | 33 +++++++++++++++++++++++++--------
>  1 file changed, 25 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
> index e5e29f8..895140f 100644
> --- a/fs/ecryptfs/crypto.c
> +++ b/fs/ecryptfs/crypto.c
> @@ -1389,19 +1389,36 @@ int ecryptfs_read_xattr_region(char *page_virt, struct inode *ecryptfs_inode)
>  int ecryptfs_read_and_validate_xattr_region(struct dentry *dentry,
>  					    struct inode *inode)
>  {
> -	u8 file_size[ECRYPTFS_SIZE_AND_MARKER_BYTES];
> -	u8 *marker = file_size + ECRYPTFS_FILE_SIZE_BYTES;
> +	char *page_virt;
>  	int rc;
>  
> +	page_virt = kmem_cache_alloc(ecryptfs_header_cache, GFP_USER);
> +	if (!page_virt) {
> +		rc = -ENOMEM;
> +		printk(KERN_ERR "%s: Unable to allocate page_virt\n",
> +		       __func__);
> +		goto out;
> +	}
>  	rc = ecryptfs_getxattr_lower(ecryptfs_dentry_to_lower(dentry),
>  				     ecryptfs_inode_to_lower(inode),
> -				     ECRYPTFS_XATTR_NAME, file_size,
> -				     ECRYPTFS_SIZE_AND_MARKER_BYTES);
> -	if (rc < ECRYPTFS_SIZE_AND_MARKER_BYTES)
> -		return rc >= 0 ? -EINVAL : rc;
> -	rc = ecryptfs_validate_marker(marker);
> +				     ECRYPTFS_XATTR_NAME, page_virt,
> +				     ECRYPTFS_DEFAULT_EXTENT_SIZE);

I worry that the ecryptfs_header_cache size and
ECRYPTFS_DEFAULT_EXTENT_SIZE aren't tied together in any way. What do
you think about using ecryptfs_header_cache->size instead of
ECRYPTFS_DEFAULT_EXTENT_SIZE here?

I think you probably copied this call to ecryptfs_getxattr_lower() from
elsewhere in fs/ecryptfs/* so I wouldn't expect you to have use
ecryptfs_header_cache->size but maybe we should correct it before making
the same mistake twice.

> +	if (rc < 0) {
> +		if (unlikely(ecryptfs_verbosity > 0))
> +			printk(KERN_INFO "Error attempting to read the [%s] "
> +			       "xattr from the lower file; return value = "
> +			       "[%d]\n", ECRYPTFS_XATTR_NAME, rc);
> +		rc = -EINVAL;

Why not pass rc up from ecryptfs_getxattr_lower() instead of masking its
error with -EINVAL?

> +		goto out;
> +	}

Lets make sure that rc is greater than or equal to
ECRYPTFS_FILE_SIZE_AND_MARKER_BYTES before proceeding.

> +	rc = ecryptfs_validate_marker(page_virt + ECRYPTFS_FILE_SIZE_BYTES);
>  	if (!rc)
> -		ecryptfs_i_size_init(file_size, inode);
> +		ecryptfs_i_size_init(page_virt, inode);
> +out:
> +	if (page_virt) {
> +		memset(page_virt, 0, PAGE_SIZE);

I don't feel like a memset() is needed here since the header metadata is
not considered to be secret in itself. All secrets are encrypted.

Tyler

> +		kmem_cache_free(ecryptfs_header_cache, page_virt);
> +	}
>  	return rc;
>  }
>  
>

Attachment: signature.asc
Description: OpenPGP digital signature