CVE-2024-35981: virtio_net: Do not send RSS key if it is not supported
First published: Mon May 20 2024(Updated: )
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.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| debian/linux | 5.10.223-1 5.10.226-1 6.1.106-3 6.1.112-1 6.10.11-1 6.11.2-1 |
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Reference Links
- https://git.kernel.org/stable/c/059a49aa2e25c58f90b50151f109dd3c4cdb3a47
- https://git.kernel.org/stable/c/28e9a64638cd16bc1ecac9ff74ffeacb9fb652de
- https://git.kernel.org/stable/c/43a71c1b4b3a6d4db857b1435d271540279fc7de
- https://git.kernel.org/stable/c/539a2b995a4ed93125cb0efae0f793b00ab2158b
- https://launchpad.net/bugs/cve/CVE-2024-35981
- https://git.kernel.org/linus/059a49aa2e25c58f90b50151f109dd3c4cdb3a47
- https://security-tracker.debian.org/tracker/CVE-2024-35981
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-35981
- https://nvd.nist.gov/vuln/detail/CVE-2024-35981
- https://ubuntu.com/security/CVE-2024-35981
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