On 11/19/20 3:54 PM, Jin Yan wrote:

On 2020/11/13 22:33, Michal Privoznik wrote:

On 11/13/20 10:47 AM, Jin Yan wrote:

Hi Michal,
I found this problem while performing migration, based on
      libvirt version: 6.2.0
      SELinux mode: permissive

Steps:
1. start a vm configured with pipe-type serial port.
      <serial type='pipe'>
        <source path='/tmp/test_pipe'/>
        <target type='system-serial' port='1'>
          <model name='pl011'/>
        </target>
      </serial>
2. migrate vm to Dst-side where no '/tmp/test_pipe' exits.
3. migration failed in Dst-side qemuProcessLaunch, and the path's label
that
has been set is not restored ('/var/lib/libvirt/qemu/nvram/XXX.fd').

I have no idea why 2)rollback you mentioned didn't work.

I'm not sure. I could not reproduce with the current master. Is it
possible for you to try the master?

Michal

I think we can reproduce it in a more easier way, that is, starting a VM 
whose XML is configured with a pipe file that does not exist on local host:
     <serial type='pipe'>
        <source path='/tmp/serial.pipe'/>
        <target port='0'/>
      </serial>

This is what I have in XML:

     <serial type='pipe'>
       <source path='/tmp/test_pipe'/>
       <target type='isa-serial' port='0'>
         <model name='isa-serial'/>
       </target>
     </serial>

and the file doesn't exist.

1. Though '/tmp/serial.pipe' does not exist, this secdriver (if I'm not 
mistaken about this concept) set SELinux-label return success, and the 
marked items (eg. XXX.fd, XXX.iso) will not be rollback.

[call trace]:
virSecuritySELinuxTransactionRun       -- return 0
     virSecuritySELinuxSetFilecon           -- return 0
         virSecuritySELinuxSetFileconImpl   -- return 1, warned unable 
to ...

I don't get a warning. I get a regular error:

error: unable to set security context 
'unconfined_u:object_r:svirt_image_t:s0:c339,c673' on '/tmp/test_pipe': 
No such file or directory

I guess the reason you got the error is that your SELinux mode is enforcing
but mine is permissive. The two modes are processed differently in 
virSecuritySELinuxSetFileconImpl().

2. The next secdriver about setting DAC-label run in 
virSecurityDACTransactionRun() return false because above file does not 
exist.

Oh I think get it now. So if one secdriver would fail but not the other 
then because of transactions the rollback would be ineffective?

If one secdriver success (maybe should fail?) and the next fail, which 
function cotrols rollback? virSecurityManagerTransactionCommit() is 
executed after virSecurityStackSetAllLabel(), but the rollback
（virSecurityManagerTransactionAbort) can't restore label.

virSecurityManagerTransactionCommit() return false, but where is the 
rollback performed for other secdrivers (here means setting 
SELinux-label in 1) ? I don't quite understand the second point you 
mentioned in your last reply:
     ---
     2) rollback for other secdrivers after one failed is handled in 
virSecurityStackSetAllLabel().
     ---

In addition, is there any wrong in virSecuritySELinuxTransactionRun 
return success while '/tmp/serial.pipe' does not exist?

I guess that is the source of problem. Have you tried the latest release 
(or master)?

I can't use the latest release for the time being, but I compared the code
and think the problem may still exist. 

Yan