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

What is CVE-2024-35981?

CVE-2024-35981 is a medium-severity denial of service vulnerability in Linux kernel, published on 20 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official 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");

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

vdev->broken = true;

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

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

9) The kernel is waiting doing the following :

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

10) 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.

Weakness: CWE-835

Which versions are affected by CVE-2024-35981?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2024-35981?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2024-35981 being exploited?

There is no known exploitation of CVE-2024-35981 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2024-35981, DEBIAN-CVE-2024-35981, GHSA-vvc7-qvmv-vpjw, UBUNTU-CVE-2024-35981.