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

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Date:   Sat, 14 Oct 2017 11:00:32 +0800
From:   Jason Xing <kerneljasonxing@...il.com>
To:     ecryptfs@...r.kernel.org
Cc:     Tyler Hicks <tyhicks@...onical.com>, linux-kernel@...r.kernel.org,
        Jason Xing <kerneljasonxing@...il.com>
Subject: Re: [PATCH] ecryptfs: Fix stat command displays wrong file size in
 xattr region

Could anyone take a look at this patch which fixes the xattr-read
issue? Thanks anyway.

Jason

On Thu, Jun 22, 2017 at 3:21 PM, Jason Xing <kerneljasonxing@...il.com> 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@...il.com>
> ---
>  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);
> +       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;
> +               goto out;
> +       }
> +       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);
> +               kmem_cache_free(ecryptfs_header_cache, page_virt);
> +       }
>         return rc;
>  }
>
> --
> 2.7.4
>