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CVE-2024-35981

Disclosure Date: May 20, 2024 •
CVE-2024-35981
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Description

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.

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CVSS V3 Severity and Metrics
Base Score:
None
Impact Score:
Unknown
Exploitability Score:
Unknown
Vector:
Unknown
Attack Vector (AV):
Unknown
Attack Complexity (AC):
Unknown
Privileges Required (PR):
Unknown
User Interaction (UI):
Unknown
Scope (S):
Unknown
Confidentiality (C):
Unknown
Integrity (I):
Unknown
Availability (A):
Unknown

General Information

Offensive Application
Unknown
Utility Class
Unknown
Ports
Unknown
OS
Unknown
Vulnerable Versions
Linux 539a2b995a4e
Linux not down converted
Prerequisites
Unknown
Discovered By
Unknown
PoC Author
Unknown
Metasploit Module
Unknown
Reporter
Unknown

Vendors

  • Linux

Products

  • Linux
Technical Analysis