Attacker Value
Unknown
(0 users assessed)
Exploitability
Unknown
(0 users assessed)
User Interaction
None
Privileges Required
Low
Attack Vector
Local
0

CVE-2022-48853

Disclosure Date: July 16, 2024
Add MITRE ATT&CK tactics and techniques that apply to this CVE.

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 virtio-scsi device
    and the buffer allocated by SG is mapped by the function
    virtqueue_add_split() which uses DMA_FROM_DEVICE for the “in” sgs (here
    scatter-gather and not scsi generics). This mapping involves bouncing
    via the swiotlb (we need swiotlb to do virtio in protected guest like
    s390 Secure Execution, or AMD SEV).
  4. When the SCSI TUR is done, we first copy back the content of the second
    (that is swiotlb) bounce buffer (which most likely contains some
    previous IO data), to the first bounce buffer, which contains all
    zeros. Then we copy back the content of the first bounce buffer to
    the user-space buffer.
  5. The test case detects that the buffer, which it zero-initialized,
    ain’t all zeros and fails.

One can argue that this is an swiotlb problem, because without swiotlb
we leak all zeros, and the swiotlb should be transparent in a sense that
it does not affect the outcome (if all other participants are well
behaved).

Copying the content of the original buffer into the swiotlb buffer is
the only way I can think of to make swiotlb transparent in such
scenarios. So let’s do just that if in doubt, but allow the driver
to tell us that the whole mapped buffer is going to be overwritten,
in which case we can preserve the old behavior and avoid the performance
impact of the extra bounce.

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CVSS V3 Severity and Metrics
Base Score:
5.5 Medium
Impact Score:
3.6
Exploitability Score:
1.8
Vector:
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Attack Vector (AV):
Local
Attack Complexity (AC):
Low
Privileges Required (PR):
Low
User Interaction (UI):
None
Scope (S):
Unchanged
Confidentiality (C):
High
Integrity (I):
None
Availability (A):
None

General Information

Vendors

  • linux

Products

  • linux kernel
Technical Analysis