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Bug 1378290 - Libvirt didn't check Multiplication overflow when check if socket*core*thread equal maxvcpu number
Summary: Libvirt didn't check Multiplication overflow when check if socket*core*thread...
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: libvirt
Version: 7.3
Hardware: x86_64
OS: Linux
low
low
Target Milestone: rc
: ---
Assignee: Peter Krempa
QA Contact: Jingjing Shao
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2016-09-22 03:43 UTC by Luyao Huang
Modified: 2017-08-01 23:57 UTC (History)
5 users (show)

Fixed In Version: libvirt-2.5.0-1.el7
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2017-08-01 17:16:43 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHEA-2017:1846 0 normal SHIPPED_LIVE libvirt bug fix and enhancement update 2017-08-01 18:02:50 UTC

Description Luyao Huang 2016-09-22 03:43:16 UTC 
Description of problem:
Libvirt didn't check Multiplication overflow when check if socket*core*thread equal maxvcpu number and this cause a strange problem

Version-Release number of selected component (if applicable):

libvirt-2.0.0-10.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. edit guest xml and make cpu topology like this:

# virsh  dumpxml r7
...
 <vcpu placement='static' current='4'>12</vcpu>
...
 <topology sockets='2' cores='4294967293' threads='4294967294'/>
...


2. start guest:

# virsh start r7
error: Failed to start domain r7
error: internal error: unable to execute QEMU command 'device_add': Invalid CPU core-id: 1 must be in range 0:4294967292

Actual results:

Libvirt have a check for vcpu topology during parse xml (validate):

...
    if (def->cpu && def->cpu->sockets) {
        topologycpus = def->cpu->sockets * def->cpu->cores * def->cpu->threads;
        if (topologycpus != virDomainDefGetVcpusMax(def)) {
            /* presence of query-hotpluggable-cpus should be a good enough witness */
...

But didn't check if there is a Multiplication overflow problem

Expected results:

Don't allow define a guest like this, since 4294967293 * 4294967294 * 2 != 12

Additional info:
Comment 1 Peter Krempa 2016-10-11 12:22:47 UTC 
Fixed upstream:

commit da0d82d15fd86ca3ed28ec2820fdb824cf92ae91
Author: Peter Krempa <pkrempa>
Date:   Mon Oct 10 15:46:25 2016 +0200

    conf: Sanitize cpu topology numbers
    
    Make sure that the topology results into a sane number of cpus (up to
    UINT_MAX) so that it can be sanely compared to the vcpu count of the VM.
    
    Additionally the helper added in this patch allows to fetch the total
    number the topology results to so that it does not have to be
    reimplemented later.
Comment 3 Jingjing Shao 2016-12-23 07:56:37 UTC 
Verify this bug as below: 

# rpm -q libvirt
libvirt-2.5.0-1.el7.x86_64



(1) define the domain

# cat rhel7.3-cpu.xml   | grep cpu -A8
...
 <vcpu placement='static' current='4'>12</vcpu>
...
 <cpu>
   <topology sockets='2' cores='4294967293' threads='4294967294'/>
 </cpu>
....


# virsh define rhel7.3-cpu.xml
error: Failed to define domain from rhel7.3-cpu.xml
error: unsupported configuration: cpu topology results in more than 4294967295 cpus


(2) edit the domain
# virsh list --all
 Id    Name                           State
----------------------------------------------------
 -     rhel7.3                        shut off


edit the xml of domain
...
 <vcpu placement='static' current='4'>12</vcpu>
...
 <cpu>
   <topology sockets='2' cores='4294967293' threads='4294967294'/>
 </cpu>
....



# virsh edit rhel7.3
error: unsupported configuration: cpu topology results in more than 4294967295 cpus
Failed. Try again? [y,n,i,f,?]: 


The result is as expected. so change the status to verified
Comment 4 errata-xmlrpc 2017-08-01 17:16:43 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2017:1846
Comment 5 errata-xmlrpc 2017-08-01 23:57:38 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2017:1846
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