# CVE-2022-48853: linux: In the Linux kernel, the following vulnerability has been resolved:  swiotlb: fix info leak with DMA_FROM_DEVICE  The...

CVE-2022-48853 is fixed in linux on 1 platform, first by DEBIAN-CVE-2022-48853, released July 16, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2022-48853
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0027
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 16, 2024

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.16.18-1 | [DEBIAN-CVE-2022-48853](https://patchblox.com/security/data/fix/linux/debian-cve-2022-48853.md) | Jul 16, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.16.18-1 | [DEBIAN-CVE-2022-48853](https://patchblox.com/security/data/fix/linux/debian-cve-2022-48853.md) | Jul 16, 2024 |
| Linux | linux Debian 14 | 5.16.18-1 | [DEBIAN-CVE-2022-48853](https://patchblox.com/security/data/fix/linux/debian-cve-2022-48853.md) | Jul 16, 2024 |

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