Re: [Qemu-devel] 'sys_rawio' selinux alarm triggered while doing SCSI reservation inside the guest

[Paolo Bonzini]

On 24/01/19 11:26, Stefan Hajnoczi wrote:
> On Thu, Jan 24, 2019 at 01:32:49AM +0000, Zhangbo (Oscar) wrote:
>> When performing SCSI reservation inside the guest, 'sys_rawio' selinux alarm 
>> is triggered, shown as below:
>> "type=AVC msg=audit(1548231520.416:8086): avc: denied { sys_rawio } for 
>> pid=30357 comm="worker" capability=17 
>> scontext=system_u:system_r:svirt_t:s0:c72,c348 
>> tcontext=system_u:system_r:svirt_t:s0:c72,c348 tclass=capability"
>>
>> It's quite possible that the *ioctl SG_IO * caused this problem.
>> Is it a design flaw in qemu? Ioctl SG_IO seems too privileged for qemu?
> 
> CCing Paolo and John for SCSI.
> 
>>
>> Here comes the possible solutions:
>>   possible solution 1: Add an selinux policy boolean to allow the 
>> 'sys_rawio' action, which suggests that this scenario is not a 
>> problem/design flaw indeed.
>>   possible solution 2: reconstruct the SCSI-related action scheme inside 
>> qemu? such as letting libvirtd to accomplish such SG_IO job.
>> Or, otherwise, any other solutions can you suggest? Thanks!

The latest QEMU already has qemu-pr-helper in order to support this.
libvirt will start the helper and tell QEMU to redirect reservations there.

You need to add "<reservations managed='yes'/>" inside the <source>
element of the disk.

Thanks,

Paolo

>>
>>
>> reproduction:
>> libvirt version: lastest
>> qemu version: lastest
>> selinux mode: Permissive
>> service auditd status: active(running)
>>
>> step 1. Configure scsi disk for vm in xml.
>> <controller type='scsi' index='0' model='virtio-scsi'>
>> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
>> </controller>
>> <disk type='block' device='lun' rawio='yes'>
>> <driver name='qemu' type='raw' cache='none' io='native'/>
>> <source dev='/dev/sdo'/>
>> <target dev='sda' bus='scsi'/>
>> <address type='drive' controller='0' bus='0' target='0' unit='0'/>
>> </disk>
>>
>> step 2. Define and start vm.
>> The type of guest OS is not the key. here is centos-7.4
>>
>> step 3. Perform SCSI reservation command inside the guest.
>> # sg_persist -o -n -I -K 123abc -S 0 -d /dev/sda
>> # sg_persist -n -o -L -K 123abc -T 5 -d /dev/sda
>> # sg_persist -o -n -I -K 123abc -S 0 -d /dev/sda
>> # sg_persist -o -n -I -S 123abc -d /dev/sda
>> # sg_persist -i -n -k -d /dev/sda
>> # sg_persist -n -o -R -T 5 -K 123abc -d /dev/sda
>> # sg_persist -n -i -r -d /dev/sda
>> # sg_persist -n -o -L -K 123abc -T 5 -d /dev/sda
>>
>> Then we can read 'sys_rawio' SElinux Denied in /var/log/audit/audit.log
>> type=AVC msg=audit(1548231520.416:8086): avc: denied { sys_rawio } for 
>> pid=30357 comm="worker" capability=17 
>> scontext=system_u:system_r:svirt_t:s0:c72,c348 
>> tcontext=system_u:system_r:svirt_t:s0:c72,c348 tclass=capability
>>

signature.asc
Description: OpenPGP digital signature