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 <casca...@canonical.com> Thu, 15 Nov
2018 17:01:46 -0200
** Changed in: linux (Ubuntu Bionic)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1801924
Title:
CVE-2018-18955: nested user namespaces with more than five extents
incorrectly grant privileges over inode
Status in linux package in Ubuntu:
Fix Committed
Status in linux source package in Bionic:
Fix Released
Status in linux source package in Cosmic:
Fix Released
Status in linux source package in Disco:
Fix Committed
Bug description:
Jann Horn reported that nested user namespaces with more than five
mappings allow gaining privilege over an inode.
Here is my write up of how this happens:
Currently, the forward map and reverse map are copied and sorted at the same
time before necessary updates to the forward map have been performed. This has
the consequence that the forward map receives the necessary updates while the
reverse map does not leaving it with invalid data. Specifically, this means
that the lower ids of the forward mapping will be correctly mapped to
appropriate kernel ids, while the lower ids of the reverse mapping will not.
This breaks inode_owner_or_capable() and privileged_wrt_inode_uidgid()
which call helpers that need to access the reverse mapping. Thus, a
process can incorrectly appear to be capable relative to an inode.
Note that the sorting logic is only triggered when more than five
extents are specified and when user namespaces are nested. Hence, only
containers with complex mappings in nested user namespaces are
affected.
To fix this issue we need to ensures that the translation happens for
both the forward and reverse mappings. First, the forward mappings are
sorted and its lower ids translated into kernel ids. After this the
forward mapping is copied and into the reverse mapping and the reverse
mappings sorted.
A proposed patch is appended here.
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