CVE-2024-35981

Published: 20 May 2024

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.

Status

References

• https://www.cve.org/CVERecord?id=CVE-2024-35981
• https://git.kernel.org/linus/059a49aa2e25c58f90b50151f109dd3c4cdb3a47 (6.9-rc4)
• https://git.kernel.org/stable/c/539a2b995a4ed93125cb0efae0f793b00ab2158b
• https://git.kernel.org/stable/c/43a71c1b4b3a6d4db857b1435d271540279fc7de
• https://git.kernel.org/stable/c/28e9a64638cd16bc1ecac9ff74ffeacb9fb652de
• https://git.kernel.org/stable/c/059a49aa2e25c58f90b50151f109dd3c4cdb3a47
• https://ubuntu.com/security/notices/USN-6893-1
• https://ubuntu.com/security/notices/USN-6893-2
• https://ubuntu.com/security/notices/USN-6893-3
• https://ubuntu.com/security/notices/USN-6918-1
• NVD
• Launchpad
• Debian