In the Linux kernel, the following vulnerability has been resolved:

xen/netback: don't queue unlimited number of packages

In case a guest isn't consuming incoming network traffic as fast as it
is coming in, xen-netback is buffering network packages in unlimited
numbers today. This can result in host OOM situations.

Commit f48da8b14d04ca8 ("xen-netback: fix unlimited guest Rx internal
queue and carrier flapping") meant to introduce a mechanism to limit
the amount of buffered data by stopping the Tx queue when reaching the
data limit, but this doesn't work for cases like UDP.

When hitting the limit don't queue further SKBs, but drop them instead.
In order to be able to tell Rx packages have been dropped increment the
rx_dropped statistics counter in this case.

It should be noted that the old solution to continue queueing SKBs had
the additional problem of an overflow of the 32-bit rx_queue_len value
would result in intermittent Tx queue enabling.

This is part of XSA-392

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-47581
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2021/CVE-2021-47581.mbox
https://git.kernel.org/stable/c/0928efb09178e01d3dc8e8849aa1c807436c3c37
https://git.kernel.org/stable/c/b4226b387436315e7f57465c15335f4f4b5b075d
https://git.kernel.org/stable/c/9bebb2eedf679b3be4acaa20efda97f32c999d74
https://git.kernel.org/stable/c/c9f17e92917fd5786be872626a3928979ecc4c39
https://git.kernel.org/stable/c/0d99b3c6bd39a0a023e972d8f912fd47698bbbb8
https://git.kernel.org/stable/c/88f20cccbeec9a5e83621df5cc2453b5081454dc
https://git.kernel.org/stable/c/bd926d189210cd1d5b4e618e45898053be6b4b3b
https://git.kernel.org/stable/c/be81992f9086b230623ae3ebbc85ecee4d00a3d3
https://www.cve.org/CVERecord?id=CVE-2021-47581