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[Launchpad Bug Tracker <1800849@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package linux - 4.15.0-42.45

---------------
linux (4.15.0-42.45) bionic; urgency=medium

  * linux: 4.15.0-42.45 -proposed tracker (LP: #1803592)

  * [FEAT] Guest-dedicated Crypto Adapters (LP: #1787405)
    - KVM: s390: reset crypto attributes for all vcpus
    - KVM: s390: vsie: simulate VCPU SIE entry/exit
    - KVM: s390: introduce and use KVM_REQ_VSIE_RESTART
    - KVM: s390: refactor crypto initialization
    - s390: vfio-ap: base implementation of VFIO AP device driver
    - s390: vfio-ap: register matrix device with VFIO mdev framework
    - s390: vfio-ap: sysfs interfaces to configure adapters
    - s390: vfio-ap: sysfs interfaces to configure domains
    - s390: vfio-ap: sysfs interfaces to configure control domains
    - s390: vfio-ap: sysfs interface to view matrix mdev matrix
    - KVM: s390: interface to clear CRYCB masks
    - s390: vfio-ap: implement mediated device open callback
    - s390: vfio-ap: implement VFIO_DEVICE_GET_INFO ioctl
    - s390: vfio-ap: zeroize the AP queues
    - s390: vfio-ap: implement VFIO_DEVICE_RESET ioctl
    - KVM: s390: Clear Crypto Control Block when using vSIE
    - KVM: s390: vsie: Do the CRYCB validation first
    - KVM: s390: vsie: Make use of CRYCB FORMAT2 clear
    - KVM: s390: vsie: Allow CRYCB FORMAT-2
    - KVM: s390: vsie: allow CRYCB FORMAT-1
    - KVM: s390: vsie: allow CRYCB FORMAT-0
    - KVM: s390: vsie: allow guest FORMAT-0 CRYCB on host FORMAT-1
    - KVM: s390: vsie: allow guest FORMAT-1 CRYCB on host FORMAT-2
    - KVM: s390: vsie: allow guest FORMAT-0 CRYCB on host FORMAT-2
    - KVM: s390: device attrs to enable/disable AP interpretation
    - KVM: s390: CPU model support for AP virtualization
    - s390: doc: detailed specifications for AP virtualization
    - KVM: s390: fix locking for crypto setting error path
    - KVM: s390: Tracing APCB changes
    - s390: vfio-ap: setup APCB mask using KVM dedicated function
    - s390/zcrypt: Add ZAPQ inline function.
    - s390/zcrypt: Review inline assembler constraints.
    - s390/zcrypt: Integrate ap_asm.h into include/asm/ap.h.
    - s390/zcrypt: fix ap_instructions_available() returncodes
    - s390/zcrypt: remove VLA usage from the AP bus
    - s390/zcrypt: Remove deprecated ioctls.
    - s390/zcrypt: Remove deprecated zcrypt proc interface.
    - s390/zcrypt: Support up to 256 crypto adapters.
    - [Config:] Enable CONFIG_S390_AP_IOMMU and set CONFIG_VFIO_AP to module.

  * Bypass of mount visibility through userns + mount propagation (LP: #1789161)
    - mount: Retest MNT_LOCKED in do_umount
    - mount: Don't allow copying MNT_UNBINDABLE|MNT_LOCKED mounts

  *  CVE-2018-18955: nested user namespaces with more than five extents
    incorrectly grant privileges over inode (LP: #1801924) // CVE-2018-18955
    - userns: also map extents in the reverse map to kernel IDs

  * kdump fail due to an IRQ storm (LP: #1797990)
    - SAUCE: x86/PCI: Export find_cap() to be used in early PCI code
    - SAUCE: x86/quirks: Add parameter to clear MSIs early on boot
    - SAUCE: x86/quirks: Scan all busses for early PCI quirks

 -- Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>  Thu, 15 Nov
2018 17:01:46 -0200

** Changed in: linux (Ubuntu Bionic)
       Status: Fix Committed => Fix Released

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-18955

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https://bugs.launchpad.net/bugs/1800849

Title:
  [Ubuntu] kvm: fix deadlock when killed by oom

Status in Ubuntu on IBM z Systems:
  Fix Committed
Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Xenial:
  Fix Released
Status in linux source package in Bionic:
  Fix Released
Status in linux source package in Cosmic:
  Fix Released

Bug description:
  == SRU Justification ==

  Description: kvm: fix deadlock when killed by oom
  Symptom: oom killer leaves processes in a deadlock state.
  Problem: The problem arises in the rare cases in which
           handle_mm_fault does not release the mm_sem.
  Solution: Correct the issue by manually release the mm_sem when needed.

  == Fix ==

  306d6c49ac9ded11114cb53b0925da52f2c2ada1 ("s390/kvm: fix deadlock when
  killed by oom")

  == Patch ==

  commit 306d6c49ac9ded11114cb53b0925da52f2c2ada1
  Author: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxxxxxxx>
  Date:   Mon Jul 16 10:38:57 2018 +0200

      s390/kvm: fix deadlock when killed by oom
      
      When the oom killer kills a userspace process in the page fault handler
      while in guest context, the fault handler fails to release the mm_sem
      if the FAULT_FLAG_RETRY_NOWAIT option is set. This leads to a deadlock
      when tearing down the mm when the process terminates. This bug can only
      happen when pfault is enabled, so only KVM clients are affected.
      
      The problem arises in the rare cases in which handle_mm_fault does not
      release the mm_sem. This patch fixes the issue by manually releasing
      the mm_sem when needed.
      
      Fixes: 24eb3a824c4f3 ("KVM: s390: Add FAULT_FLAG_RETRY_NOWAIT for guest fault")
      Cc: <stable@xxxxxxxxxxxxxxx> # 3.15+
      Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxxxxxxx>
      Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

  == Regression Potential ==

  Low and minimal, because:

  - code change is s390x only
  - limited to one single file: /arch/s390/mm/fault.c
  - just two additional lines added (if stmt)
  - Xenial and Cosmic already have this commit via upstream stable updates.
  - Hence patch is just missing in Bionic.
  - Test kernel was build for testting.

  == Test Case ==

  Create numerous KVM guests so that the host starts swapping
  and memory becomes overcomitted and the oom killer is triggered.
  __________

  Description:  kvm: fix deadlock when killed by oom

  Symptom:      oom killer leaves processes in a deadlock state.

  Problem:      The problem arises in the rare cases in which
                    handle_mm_fault does not release the mm_sem.

  Solution:     Correct the issue by manually relaese the mm_sem
                    when needed.

  Reproduction: Create numerous KVM guests so that the host starts
                    swapping and memory becomes overcomitted and the oom
                    killer is triggered.

  kernel 4.19
  Upstream-ID:  306d6c49ac9ded11114cb53b0925da52f2c2ada1

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