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CVE-2024-35981 Affecting kernel-rt-trace-kvm package, versions *

Severity

 Recommended
low

Based on CentOS security rating.

Threat Intelligence

EPSS
0.05% (18th percentile)

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  • Snyk IDSNYK-CENTOS7-KERNELRTTRACEKVM-6962990
  • published21 May 2024
  • disclosed20 May 2024
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Introduced: 20 May 2024

CVE-2024-35981  (opens in a new tab)

How to fix?

There is no fixed version for Centos:7 kernel-rt-trace-kvm.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-rt-trace-kvm package and not the kernel-rt-trace-kvm package as distributed by Centos. See How to fix? for Centos:7 relevant fixed versions and status.

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:

  1. ethtool_set_rxfh() calls virtnet_set_rxfh()

  2. virtnet_set_rxfh() calls virtnet_commit_rss_command()

  3. virtnet_commit_rss_command() populates 4 entries for the rss scatter-gather

  4. 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;

  5. 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");

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

    vdev->broken = true;

  2. Qemu bails out, and do not repond this crazy kernel.

  3. The kernel is waiting for the response to come back (function virtnet_send_command())

  4. The kernel is waiting doing the following :

    while (!virtqueue_get_buf(vi->cvq, &tmp) && !virtqueue_is_broken(vi->cvq)) cpu_relax();

  5. 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.

CVSS Scores

version 3.1