fbcbbe78dc
FAT specification requires that for valid FAT, FAT cluster 0 has a specific value derived from the BPB media descriptor. The lowest (little-endian) byte must be equal to bpb.bpbMedia, other bits in the cluster number must be all 1's. Implement the check to reduce the chance of the randomly corrupted FAT to pass the mount attempt. Submitted by: Siva Mahadevan <smahadevan@freebsdfoundation.org> MFC after: 2 weeks Differential revision: https://reviews.freebsd.org/D12124