Re: [PATCH V2] xfs: fix boundary test in xfs_attr_shortform_verify

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Aug 26, 2020 at 11:19:54AM -0500, Eric Sandeen wrote:
> The boundary test for the fixed-offset parts of xfs_attr_sf_entry in
> xfs_attr_shortform_verify is off by one, because the variable array
> at the end is defined as nameval[1] not nameval[].
> Hence we need to subtract 1 from the calculation.
> 
> This can be shown by:
> 
> # touch file
> # setfattr -n root.a file
> 
> and verifications will fail when it's written to disk.
> 
> This only matters for a last attribute which has a single-byte name
> and no value, otherwise the combination of namelen & valuelen will
> push endp further out and this test won't fail.
> 
> Fixes: 1e1bbd8e7ee06 ("xfs: create structure verifier function for shortform xattrs")
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>

Looks ok.

From whom should I be expecting a test case?

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
> 
> V2: Add whitespace and comments, tweak commit log.
> 
> Note: as Darrick points out, this should be made consistent w/ the dir2 arrays
> by making the nameval variable size array [] not [1], and then we can lose all
> the -1 magic sprinkled around.  At that time we should probably also make the
> macros into proper functions, as was done for dir2.
> 
> For now, this is just the least invasive fixup for the problem at hand.
> 
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> index 8623c815164a..383b08f2ac61 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -1036,8 +1036,10 @@ xfs_attr_shortform_verify(
>  		 * struct xfs_attr_sf_entry has a variable length.
>  		 * Check the fixed-offset parts of the structure are
>  		 * within the data buffer.
> +		 * xfs_attr_sf_entry is defined with a 1-byte variable
> +		 * array at the end, so we must subtract that off.
>  		 */
> -		if (((char *)sfep + sizeof(*sfep)) >= endp)
> +		if (((char *)sfep + sizeof(*sfep) - 1) >= endp)
>  			return __this_address;
>  
>  		/* Don't allow names with known bad length. */
>