xfs: fix boundary test in xfs_attr_shortform_verify

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>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
index 8623c81..383b08f 100644 (file)
--- 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. */