Bug 1671904 (CVE-2019-7221) - CVE-2019-7221 Kernel: KVM: nVMX: use-after-free of the hrtimer for emulation of the preemption timer
Summary: CVE-2019-7221 Kernel: KVM: nVMX: use-after-free of the hrtimer for emulation ...
Status: NEW
Alias: CVE-2019-7221
Product: Security Response
Classification: Other
Component: vulnerability   
(Show other bugs)
Version: unspecified
Hardware: All
OS: Linux
high
high
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard: impact=important,public=20190207,repo...
Keywords: Security
Depends On: 1671905 1671906 1671907 1671908 1673841 1673842 1673676
Blocks: 1671898
TreeView+ depends on / blocked
 
Reported: 2019-02-02 05:20 UTC by Prasad J Pandit
Modified: 2019-02-25 17:20 UTC (History)
44 users (show)

Fixed In Version:
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A use-after-free vulnerability was found in the way the Linux kernel's KVM hypervisor emulates a preemption timer for L2 guests when nested (=1) virtualization is enabled. This high resolution timer(hrtimer) runs when a L2 guest is active. After VM exit, the sync_vmcs12() timer object is stopped. The use-after-free occurs if the timer object is freed before calling sync_vmcs12() routine. A guest user/process could use this flaw to crash the host kernel resulting in a denial of service or, potentially, gain privileged access to a system.
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Description Prasad J Pandit 2019-02-02 05:20:00 UTC
A use after free issue was found in the way Linux kernel's KVM hypervisor
emulates a preemption timer for L2 guest when nested(=1) virtualization
is enabled. This high resolution timer(hrtimer) runs when L2 guest is active.
After VM exit, in sync_vmcs12() timer object is stopped. The use-after-free
occurs if the timer object is free'd before calling sync_vmcs12() routine.

A guest user/process could use this flaw to crash the host kernel resulting
in DoS OR potentially gain privileged access to a system.

It affects only Intel processors and only when nested virtualization is
enabled.

Upstream patch:
---------------
  -> https://git.kernel.org/linus/ecec76885bcfe3294685dc363fd1273df0d5d65f

Reference:
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  -> https://www.openwall.com/lists/oss-security/2019/02/18/2

Comment 2 Prasad J Pandit 2019-02-06 07:10:33 UTC
Acknowledgments:

Name: Felix Wilhelm (Google)

Comment 3 Prasad J Pandit 2019-02-07 11:24:21 UTC
Statement:

This issue does not affect the version of the kernel package as shipped with Red Hat Enterprise Linux 5, 6 and Red Hat Enterprise MRG 2.

This issue affects the versions of Linux kernel as shipped with Red Hat Enterprise Linux 7. Future kernel updates for Red Hat Enterprise Linux 7 may address this issue.

Note: Impact on Red Hat Enterprise Linux 7 kernel is limited, as it requires that nested virtualization feature is enabled on a system. Nested Virtualization feature is available only as - Technology Preview.

Comment 4 Prasad J Pandit 2019-02-07 18:37:12 UTC
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1673676]


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