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Bug 1939600

Summary: AVCs "denied { read } dev="nsfs" ino=4026531992 scontext=system_u:system_r:container_t:s0:c479,c590 tcontext=system_u:system_r:NetworkManager_t:s0"
Product: Red Hat Enterprise Linux 8 Reporter: Michele Baldessari <michele>
Component: container-selinuxAssignee: Daniel Walsh <dwalsh>
Status: CLOSED NOTABUG QA Contact: atomic-bugs <atomic-bugs>
Severity: medium Docs Contact:
Priority: unspecified    
Version: 8.4CC: dwalsh, jeckersb, jnovy, tsweeney
Target Milestone: rcFlags: pm-rhel: mirror+
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Hardware: Unspecified   
OS: Unspecified   
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Clone Of: Environment:
Last Closed: 2021-03-23 10:44:10 UTC Type: Bug
Regression: --- Mount Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Embargoed:

Description Michele Baldessari 2021-03-16 17:00:27 UTC
Description of problem:
The context here is that we're adding BGP support to OSP via a container that runs the network daemons (FRR). We've noticed the following denials when we start (and only at start time) of the container:

type=AVC msg=audit(1615820022.436:5242): avc: denied { read } for pid=17999 comm="zebra" dev="nsfs" ino=4026531992 scontext=system_u:system_r:container_t:s0:c479,c590
tcontext=system_u:system_r:NetworkManager_t:s0 tclass=file permissive=0

type=AVC msg=audit(1615820022.436:5243): avc: denied { read } for pid=17999 comm="zebra" dev="nsfs" ino=4026531992 scontext=system_u:system_r:container_t:s0:c479,c590 tcontext=system_u:system_r:NetworkManager_t:s0 tclass=file permissive=0

type=AVC msg=audit(1615820022.598:5245): avc: denied { read } for pid=18015 comm="bgpd" dev="nsfs" ino=4026531992 scontext=system_u:system_r:container_t:s0:c479,c590 tcontext=system_u:system_r:NetworkManager_t:s0 tclass=file permissive=0

type=AVC msg=audit(1615820022.783:5246): avc: denied { read } for pid=18024 comm="staticd" dev="nsfs" ino=4026531992 scontext=system_u:system_r:container_t:s0:c479,c590 tcontext=system_u:system_r:NetworkManager_t:s0 tclass=file permissive=0

type=AVC msg=audit(1615820022.922:5247): avc: denied { read } for pid=18029 comm="bfdd" dev="nsfs" ino=4026531992 scontext=system_u:system_r:container_t:s0:c479,c590 tcontext=system_u:system_r:NetworkManager_t:s0 tclass=file permissive=0


I dug a bit more and the inode 4026531992 is the inode backing the fd of the default network namespace:
[root@localhost ~]# ls -l /proc/1/ns/net
lrwxrwxrwx. 1 root root 0 Mar 16 12:51 /proc/1/ns/net -> 'net:[4026531992]'

I can replicate the issue with a small program that only calls open("/proc/self/ns/net") or more simply with 'cat /proc/self/ns/net' (cat makes no sense on a socket and will return 'Invalid argument' when not denied, but it makes thing simpler to reproduce):
podman  run -it --net=host --cap-add NET_BIND_SERVICE --cap-add NET_RAW --cap-add NET_ADMIN --cap-add SYS_ADMIN -u root quay.io/cloudbgp/openstack-frr:7.5 sh -c 'cat /proc/self/ns/net'

This triggers:
type=AVC msg=audit(1615913490.269:274): avc:  denied  { read } for  pid=17361 comm="cat" dev="nsfs" ino=4026531992 scontext=system_u:system_r:container_t:s0:c255,c654 tcontext=system_u:system_r:NetworkManager_t:s0 tclass=file permissive=0

Version-Release number of selected component (if applicable):
[root@localhost ~]# rpm -q podman container-selinux runc selinux-policy
podman-3.0.1-3.module+el8.4.0+10197+7c295612.x86_64
container-selinux-2.158.0-1.module+el8.4.0+10197+7c295612.noarch
runc-1.0.0-70.rc92.module+el8.4.0+10197+7c295612.x86_64
selinux-policy-3.14.3-65.el8.noarch

This is RHEL-8.4-beta1 with container-tools:3.0

How reproducible:
100%

Additional Info:
1) As soon as I do a "systemctl disable --now NetworkManager" there are no denials at all
2) This works when using --privileged but we'd like to avoid that for obvious reasons. Also CAP_SYS_ADMIN should be enough in this case? (Since it allows setns() calls)
3) This reproducer, for a reason yet not clear to me, shows no denied AVCs on Fedora 33
4) The code in FRR that is likely triggering this denial is here:
https://github.com/FRRouting/frr/blob/master/lib/netns_linux.c#L105

Comment 3 Daniel Walsh 2021-03-23 10:44:10 UTC
You should just disable SELinux for this container if you need to interact with the networkmanager on the host.  We are not going to allow this in default selinux-policy

--security-opt label=disable

Comment 4 Michele Baldessari 2021-03-27 10:45:25 UTC
(In reply to Daniel Walsh from comment #3)
> You should just disable SELinux for this container if you need to interact
> with the networkmanager on the host. 

I do not need to interact with NM on the host. But NM on the host took over /proc/self/ns/net

> We are not going to allow this in
> default selinux-policy
> 
> --security-opt label=disable

Then I guess RHEL9/Fedora are allowing more than they should, since it works just fine there.

Comment 5 Daniel Walsh 2021-03-28 11:08:59 UTC
No in those cases /proc/self/ns/net is not controlled by networkmanager_t.

 podman run -ti --rm fedora ls -lZ /proc/self/ns/net
lrwxrwxrwx. 1 root root system_u:system_r:container_t:s0:c759,c952 0 Mar 28 11:07 /proc/self/ns/net -> 'net:[4026534657]'