Kernel memory corruption via invalid NTFS index block

Out-of-bounds access in the Linux kernel NTFS driver 7.1 through 7.1.3 allows local users to corrupt kernel memory via a crafted image. The ntfs_icx_ib_sync_write function treats validation failures as write failures and calls post_write_mst_fixup on an invalid index block without boundary checks, allowing malformed usa_ofs or usa_count fields to drive out-of-bounds reads and writes. Exploitation requires local access to a mounted attacker-controlled NTFS image and a writeback or fsync trigger; consequences include kernel data disclosure, modification, and service interruption.