CVE-2024-35981 virtio_net: Do not send RSS key if it is not supported

2024-05-2009:42:05

Linux

github.com

linux kernel

vulnerability

cve

virtio_net

eth0

qemu

ethtool

bug

rss options

infinite loop

virtionet

command

scatter-gather

buffer

virtqueue

device

feature

7 High

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

15.6%

JSON

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

virtio_net: Do not send RSS key if it is not supported

There is a bug when setting the RSS options in virtio_net that can break
the whole machine, getting the kernel into an infinite loop.

Running the following command in any QEMU virtual machine with virtionet
will reproduce this problem:

# ethtool -X eth0  hfunc toeplitz

This is how the problem happens:

ethtool_set_rxfh() calls virtnet_set_rxfh()
virtnet_set_rxfh() calls virtnet_commit_rss_command()
virtnet_commit_rss_command() populates 4 entries for the rss
scatter-gather
Since the command above does not have a key, then the last
scatter-gatter entry will be zeroed, since rss_key_size == 0.
sg_buf_size = vi->rss_key_size;
This buffer is passed to qemu, but qemu is not happy with a buffer
with zero length, and do the following in virtqueue_map_desc() (QEMU
function):

if (!sz) {
virtio_error(vdev, “virtio: zero sized buffers are not allowed”);

virtio_error() (also QEMU function) set the device as broken

vdev->broken = true;
Qemu bails out, and do not repond this crazy kernel.
The kernel is waiting for the response to come back (function
virtnet_send_command())
The kernel is waiting doing the following :

while (!virtqueue_get_buf(vi->cvq, &tmp) &&
!virtqueue_is_broken(vi->cvq))
cpu_relax();
None of the following functions above is true, thus, the kernel
loops here forever. Keeping in mind that virtqueue_is_broken() does
not look at the qemu vdev->broken, so, it never realizes that the
vitio is broken at QEMU side.

Fix it by not sending RSS commands if the feature is not available in
the device.

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "drivers/net/virtio_net.c"
    ],
    "versions": [
      {
        "version": "c7114b1249fa",
        "lessThan": "539a2b995a4e",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "c7114b1249fa",
        "lessThan": "43a71c1b4b3a",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "c7114b1249fa",
        "lessThan": "28e9a64638cd",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "c7114b1249fa",
        "lessThan": "059a49aa2e25",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "drivers/net/virtio_net.c"
    ],
    "versions": [
      {
        "version": "5.18",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "5.18",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.1.90",
        "lessThanOrEqual": "6.1.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.6.29",
        "lessThanOrEqual": "6.6.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.8.7",
        "lessThanOrEqual": "6.8.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.9",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]