[refpolicy] Which labelling for namespace filesystem?

[nicolas.iooss@m4x.org (Nicolas Iooss)]

On 01/06/2016 07:44 PM, Dominick Grift wrote:
> On Wed, Jan 06, 2016 at 07:37:10PM +0100, Nicolas Iooss wrote:
>> Hello,
> 
>> On the system I'm using to get refpolicy working with Arch Linux, I have
>> these lines in audit.log:
> 
>>   type=AVC msg=audit(1451041210.334:794): avc:  denied  { read } for
>>   pid=28829 comm="(ostnamed)" dev="nsfs" ino=4026532544
>>   scontext=system_u:system_r:init_t
>>   tcontext=system_u:object_r:unlabeled_t tclass=file permissive=1
> 
>>   type=AVC msg=audit(1451041210.334:794): avc:  denied  { open } for
>>   pid=28829 comm="(ostnamed)" path="net:[4026532544]" dev="nsfs"
>>   ino=4026532544 scontext=system_u:system_r:init_t
>>   tcontext=system_u:object_r:unlabeled_t tclass=file permissive=1
> 
>> These accesses are caused by open("/proc/self/ns/net"...) in systemd
>> setup_netns() function [1].  Indeed /proc/PID/ns/* symlinks target a
>> special filesystem named nsfs which is used for setns() syscall [2].  As
>> this filesystem is not defined in refpolicy, its files are currently
>> unlabeled, which explains the audit records.
> 
>> To fix this, I see two options:
> 
>> * "fs_use_task nsfs gen_context(system_u:object_r:fs_t,s0);", so that
>> programs already allowed to access the /proc/PID tree of a process can
>> also open /proc/PID/ns/* files.
> 
>> * "genfscon nsfs / gen_context(system_u:object_r:nsfs_t,s0))", with a
>> new fs type.  Programs using setns() will then need to be granted
>> opening and reading nsfs_t files, in addition to be allowed using
>> /proc/PID/ files of the target process.
> 
> Have you tried this option? I recall having tried it, and not getting
> this to work.

Yes, in permissive mode only though.  I first added this to
kernel/filesystem.te:

  type nsfs_t;
  fs_type(nsfs_t)
  genfscon nsfs / gen_context(system_u:object_r:nsfs_t,s0)

Then (after rebooting) audit.log showed:

  type=AVC msg=audit(1452106332.300:1811): avc:  denied  { read } for
  pid=11125 comm="(ostnamed)" dev="nsfs" ino=4026532618
  scontext=system_u:system_r:init_t tcontext=system_u:object_r:nsfs_t
  tclass=file permissive=1
  type=AVC msg=audit(1452106332.300:1811): avc:  denied  { open } for
  pid=11125 comm="(ostnamed)" path="net:[4026532618]" dev="nsfs"
  ino=4026532618 scontext=system_u:system_r:init_t
  tcontext=system_u:object_r:nsfs_t tclass=file permissive=1

Adding the following lines to system/init.te in the
ifdef(`init_systemd') block made these messages disappear when running
"systemctl restart systemd-hostnamed.service":

	optional_policy(`
		gen_require(`
			type nsfs_t;
		')
		allow init_t nsfs_t:file read_file_perms;
	')

Could you please describe the problem you had, so that I can see if I
also have it?

Nicolas