[libvirt] [PATCH 3/4] security: Introduce method for labeling file descriptors of created files

[Peter Krempa]

On 06/27/13 20:51, Daniel P. Berrange wrote:
> On Wed, Jun 26, 2013 at 03:01:49PM +0200, Peter Krempa wrote:
>> The method labels the file descriptor even if dynamic labeling/relabeling
>> is turned off. This is needed for files created by libvirt and then
>> passed along to qemu as a FD.
>> ---
>>   src/libvirt_private.syms        |  1 +
>>   src/security/security_dac.c     |  9 +++++++++
>>   src/security/security_driver.h  |  4 ++++
>>   src/security/security_manager.c | 16 ++++++++++++++++
>>   src/security/security_manager.h |  3 +++
>>   src/security/security_nop.c     |  1 +
>>   src/security/security_selinux.c | 21 +++++++++++++++++++++
>>   src/security/security_stack.c   | 19 +++++++++++++++++++
>>   8 files changed, 74 insertions(+)
>>
>
>> diff --git a/src/security/security_selinux.c b/src/security/security_selinux.c
>> index 7802dda..5894259 100644
>> --- a/src/security/security_selinux.c
>> +++ b/src/security/security_selinux.c
>> @@ -2446,6 +2446,26 @@ virSecuritySELinuxGetSecurityMountOptions(virSecurityManagerPtr mgr,
>>       return opts;
>>   }
>>
>> +static int
>> +virSecuritySELinuxSetCreatedFDLabel(virSecurityManagerPtr mgr ATTRIBUTE_UNUSED,
>> +                                    virDomainDefPtr def,
>> +                                    int fd)
>> +{
>> +    virSecurityLabelDefPtr secdef;
>> +
>> +    if ((secdef = virDomainDefGetSecurityLabelDef(def, SECURITY_SELINUX_NAME))) {
>> +        if (!secdef->imagelabel)
>> +            secdef->imagelabel = virSecuritySELinuxGenImageLabel(mgr, def);
>
> This is really dubious. None of the methods except for GenSecurityLabel
> should be making changes to the secdef state.

There is already an exception: virSecuritySELinuxGetSecurityMountOptions().

>
>> +    } else {
>> +        return -1;
>> +    }
>
> The style with nested if()s here is not following the pattern used in other
> methods here either.

hmmmm ... ok

>
>> +
>> +    if (secdef->imagelabel == NULL)
>> +        return 0;
>> +
>> +    return virSecuritySELinuxFSetFilecon(fd, secdef->imagelabel);
>> +}
>
>
> In general I'm not really convinced we should be adding a new method
> here, as opposed to making the existing SetImageFDLabel do the right
> thing.

I was going to suggest expanding the function prototype with a bool that 
would allow to choose whether to label the image always or only if 
relabeling is enabled but looking through the code I noticed that 
actually every caller would need to have this flag enabled.

There are currently 4 places this method is called:

qemuDumpToFd() - labels a FD of a freshly created file for the memory dump

qemuMigrationToFile() - again a new file FD is labeled, used for 
(managed) save and dumping of memory

doTunnelMigrate() - the FD's of a pipe used for extracting data into the 
stream are labeled, again this would probably fail with static labeling.

qemuProcessStart() - the migration FD is labelled on process start.

I think it's safe (and necessary) to relabel these even if relabeling is 
disabled and thus we can change the function to always label FD's.
Do you agree?

>
> Daniel
>

Peter