CVE-2024-35981

Summary

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.

Affected Software

VendorProductVersion RangeStatus
LinuxLinuxc7114b1249fa3b5f3a434606ba4cc89c4a27d618 < 539a2b995a4ed93125cb0efae0f793b00ab2158baffected
LinuxLinuxc7114b1249fa3b5f3a434606ba4cc89c4a27d618 < 43a71c1b4b3a6d4db857b1435d271540279fc7deaffected
LinuxLinuxc7114b1249fa3b5f3a434606ba4cc89c4a27d618 < 28e9a64638cd16bc1ecac9ff74ffeacb9fb652deaffected
LinuxLinuxc7114b1249fa3b5f3a434606ba4cc89c4a27d618 < 059a49aa2e25c58f90b50151f109dd3c4cdb3a47affected
LinuxLinux5.18affected
LinuxLinux0 < 5.18unaffected
LinuxLinux6.1.90 <= 6.1.*unaffected
LinuxLinux6.6.29 <= 6.6.*unaffected
LinuxLinux6.8.7 <= 6.8.*unaffected
LinuxLinux6.9 <= *unaffected

Weaknesses

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

CVE Program Container

Additional References

References