fs/xfs: Fix issues found while fuzzing the XFS filesystem

fs/xfs: Fix issues found while fuzzing the XFS filesystem

While performing fuzz testing with XFS filesystem images with ASAN
enabled, several issues were found where the memory accesses are made
beyond the data that is allocated into the struct grub_xfs_data
structure's data field.

The existing structure didn't store the size of the memory allocated into
the buffer in the data field and had no way to check it. To resolve these
issues, the data size is stored to enable checks into the data buffer.

With these checks in place, the fuzzing corpus no longer cause any crashes.

Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Robbie Harwood <rharwood@redhat.com>
Signed-off-by: Marta Lewandowska <mlewando@redhat.com>
Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>