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             AUSCERT External Security Bulletin Redistribution

                    USN-4916-2: Linux kernel regression
                               22 April 2021


        AusCERT Security Bulletin Summary

Product:           linux kernel
Publisher:         Ubuntu
Operating System:  Ubuntu
Impact/Access:     Execute Arbitrary Code/Commands -- Existing Account
                   Increased Privileges            -- Existing Account
                   Denial of Service               -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2021-29154 CVE-2021-3493 

Reference:         ESB-2021.1300

Original Bulletin: 

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USN-4916-2: Linux kernel regression
21 April 2021

USN-4916-1 introduced a regression in the Linux kernel.

  o Ubuntu 20.04 LTS
  o Ubuntu 18.04 LTS
  o Ubuntu 16.04 LTS
  o Ubuntu 14.04 ESM


  o linux - Linux kernel
  o linux-aws - Linux kernel for Amazon Web Services (AWS) systems
  o linux-gke-5.3 - Linux kernel for Google Container Engine (GKE) systems
  o linux-hwe - Linux hardware enablement (HWE) kernel
  o linux-kvm - Linux kernel for cloud environments
  o linux-lts-xenial - Linux hardware enablement kernel from Xenial for Trusty
  o linux-oem-5.6 - Linux kernel for OEM systems
  o linux-raspi2-5.3 - Linux kernel for Raspberry Pi (V8) systems
  o linux-snapdragon - Linux kernel for Qualcomm Snapdragon processors


USN-4916-1 fixed vulnerabilities in the Linux kernel. Unfortunately,
the fix for CVE-2021-3493 introduced a memory leak in some situations.
This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

It was discovered that the overlayfs implementation in the Linux kernel did
not properly validate the application of file system capabilities with
respect to user namespaces. A local attacker could use this to gain
elevated privileges. ( CVE-2021-3493 )

Piotr Krysiuk discovered that the BPF JIT compiler for x86 in the Linux
kernel did not properly validate computation of branch displacements in
some situations. A local attacker could use this to cause a denial of
service (system crash) or possibly execute arbitrary code. ( CVE-2021-29154 )

Update instructions

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

Ubuntu 20.04

  o linux-image-5.6.0-1055-oem - 5.6.0-1055.59
  o linux-image-oem-20.04 -

Ubuntu 18.04

  o linux-image-gkeop-5.3 -
  o linux-image-gke-5.3 -
  o linux-image-5.3.0-74-lowlatency - 5.3.0-74.70
  o linux-image-5.3.0-1040-raspi2 - 5.3.0-1040.42
  o linux-image-5.3.0-74-generic - 5.3.0-74.70
  o linux-image-5.3.0-1043-gke - 5.3.0-1043.46
  o linux-image-raspi2-hwe-18.04 -

Ubuntu 16.04

  o linux-image-powerpc-smp -
  o linux-image-4.4.0-1156-snapdragon - 4.4.0-1156.166
  o linux-image-4.4.0-210-generic-lpae - 4.4.0-210.242
  o linux-image-4.4.0-210-powerpc-e500mc - 4.4.0-210.242
  o linux-image-4.4.0-1128-aws - 4.4.0-1128.142
  o linux-image-generic -
  o linux-image-4.4.0-210-powerpc64-emb - 4.4.0-210.242
  o linux-image-powerpc-e500mc -
  o linux-image-4.4.0-210-generic - 4.4.0-210.242
  o linux-image-lowlatency -
  o linux-image-powerpc64-emb -
  o linux-image-generic-lpae -
  o linux-image-powerpc64-smp -
  o linux-image-4.4.0-210-powerpc-smp - 4.4.0-210.242
  o linux-image-aws -
  o linux-image-snapdragon -
  o linux-image-4.4.0-210-lowlatency - 4.4.0-210.242
  o linux-image-kvm -
  o linux-image-4.4.0-1093-kvm - 4.4.0-1093.102
  o linux-image-4.4.0-210-powerpc64-smp - 4.4.0-210.242
  o linux-image-virtual -

Ubuntu 14.04

  o linux-image-powerpc-smp-lts-xenial -
  o linux-image-lowlatency-lts-xenial -
  o linux-image-4.4.0-210-lowlatency - 4.4.0-210.242~14.04.1
  o linux-image-4.4.0-210-powerpc-e500mc - 4.4.0-210.242~14.04.1
  o linux-image-4.4.0-210-powerpc64-emb - 4.4.0-210.242~14.04.1
  o linux-image-4.4.0-210-generic - 4.4.0-210.242~14.04.1
  o linux-image-powerpc-e500mc-lts-xenial -
  o linux-image-generic-lpae-lts-xenial -
  o linux-image-powerpc64-smp-lts-xenial -
  o linux-image-4.4.0-1092-aws - 4.4.0-1092.96
  o linux-image-powerpc64-emb-lts-xenial -
  o linux-image-4.4.0-210-powerpc-smp - 4.4.0-210.242~14.04.1
  o linux-image-aws -
  o linux-image-generic-lts-xenial -
  o linux-image-4.4.0-210-generic-lpae - 4.4.0-210.242~14.04.1
  o linux-image-4.4.0-210-powerpc64-smp - 4.4.0-210.242~14.04.1
  o linux-image-virtual-lts-xenial -

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.


  o https://launchpad.net/bugs/1924611

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