CVE-2022-48853

/// Technical description

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

swiotlb: fix info leak with DMA_FROM_DEVICE

The problem I'm addressing was discovered by the LTP test covering

cve-2018-1000204.

A short description of what happens follows:

1) The test case issues a command code 00 (TEST UNIT READY) via the SG_IO

interface with: dxfer_len == 524288, dxdfer_dir == SG_DXFER_FROM_DEV

and a corresponding dxferp. The peculiar thing about this is that TUR

is not reading from the device.

2) In sg_start_req() the invocation of blk_rq_map_user() effectively

bounces the user-space buffer. As if the device was to transfer into

it. Since commit a45b599ad808 ("scsi: sg: allocate with __GFP_ZERO in

sg_build_indirect()") we make sure this first bounce buffer is

allocated with GFP_ZERO.

3) For the rest of the story we keep ignoring that we have a TUR, so the

device won't touch the buffer we prepare as if the we had a

DMA_FROM_DEVICE type of situation. My setup uses a vir

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References