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@xxxxxxxxxx>
Looks ok.
>From whom should I be expecting a test case?
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--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. */
>
