Linux kernel: ATA passthru sense handling reads and writes past buffer

In the Linux kernel, the following vulnerability has been resolved:

ata: libata-scsi: bound the ATA passthru sense descriptor writes

When an ATA PASS-THROUGH command to an ATAPI device fails, the sense buffer holds the device's REQUEST SENSE reply, and ata_scsi_set_passthru_sense_fields() trusts its additional length byte, sb[7], when adding the ATA Status Return descriptor. A faulty or malicious device can use that to make the kernel read and write past the 96-byte buffer in three ways:

• scsi_sense_desc_find() is passed sb[7] + 8 as the buffer length, so its clamp against sb[7] does nothing and the walk runs off the end.
• A type-9 descriptor found near the end is filled in unchecked.
• A new descriptor at sb[8 + len] needs len + 22 bytes, not len + 14, so len 75..82 writes up to 8 bytes past the end.

Reproduced with KASAN under qemu, with the emulated ATAPI REQUEST SENSE reply patched:

BUG: KASAN: slab-out-of-bounds in scsi_sense_desc_find+0x1a5/0x210 BUG: KASAN: slab-out-of-bounds in ata_scsi_qc_complete+0x1a15/0x1a50

Both are gone with this patch, and a valid descriptor is still filled in.