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Ubuntu Security Notice USN-5091-3
October 15, 2021

linux-azure, linux-azure-5.4 regression
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS

Summary:

USN-5091-1 introduced a regression in the Linux kernel for Microsoft
Azure cloud systems.

Software Description:
- linux-azure: Linux kernel for Microsoft Azure Cloud systems
- linux-azure-5.4: Linux kernel for Microsoft Azure cloud systems

Details:

USN-5091-1 fixed vulnerabilities in Linux 5.4-based kernels.
Unfortunately, for Linux kernels intended for use within Microsoft
Azure environments, that update introduced a regression that could
cause the kernel to fail to boot in large Azure instance types.
This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

 Ofek Kirzner, Adam Morrison, Benedict Schlueter, and Piotr Krysiuk
 discovered that the BPF verifier in the Linux kernel missed possible
 mispredicted branches due to type confusion, allowing a side-channel
 attack. An attacker could use this to expose sensitive information.
 (CVE-2021-33624)

 It was discovered that the tracing subsystem in the Linux kernel did not
 properly keep track of per-cpu ring buffer state. A privileged attacker
 could use this to cause a denial of service. (CVE-2021-3679)

 Alexey Kardashevskiy discovered that the KVM implementation for PowerPC
 systems in the Linux kernel did not properly validate RTAS arguments in
 some situations. An attacker in a guest vm could use this to cause a denial
 of service (host OS crash) or possibly execute arbitrary code.
 (CVE-2021-37576)

 It was discovered that the Virtio console implementation in the Linux
 kernel did not properly validate input lengths in some situations. A local
 attacker could possibly use this to cause a denial of service (system
 crash). (CVE-2021-38160)

 Michael Wakabayashi discovered that the NFSv4 client implementation in the
 Linux kernel did not properly order connection setup operations. An
 attacker controlling a remote NFS server could use this to cause a denial
 of service on the client. (CVE-2021-38199)

 It was discovered that the MAX-3421 host USB device driver in the Linux
 kernel did not properly handle device removal events. A physically
 proximate attacker could use this to cause a denial of service (system
 crash). (CVE-2021-38204)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.04 LTS:
  linux-image-5.4.0-1061-azure    5.4.0-1061.64
  linux-image-azure-lts-20.04     5.4.0.1061.59

Ubuntu 18.04 LTS:
  linux-image-5.4.0-1061-azure    5.4.0-1061.64~18.04.1
  linux-image-azure               5.4.0.1061.41

After a standard system update you need to reboot your computer to make
all the necessary changes.

ATTENTION: Due to an unavoidable ABI change the kernel updates have
been given a new version number, which requires you to recompile and
reinstall all third party kernel modules you might have installed.
Unless you manually uninstalled the standard kernel metapackages
(e.g. linux-generic, linux-generic-lts-RELEASE, linux-virtual,
linux-powerpc), a standard system upgrade will automatically perform
this as well.

References:
  https://ubuntu.com/security/notices/USN-5091-3
  https://ubuntu.com/security/notices/USN-5091-1
  https://launchpad.net/bugs/1940564

Package Information:
  https://launchpad.net/ubuntu/+source/linux-azure/5.4.0-1061.64
  https://launchpad.net/ubuntu/+source/linux-azure-5.4/5.4.0-1061.64~18.04.1