[PATCH net 0/1 v3] rtnetlink: require unique netns identifier

[Christian Brauner]

Hey,

Since we've added support for IFLA_IF_NETNSID for RTM_{DEL,GET,SET,NEW}LINK
it is possible for userspace to send us requests with three different
properties to identify a target network namespace. This affects at least
RTM_{NEW,SET}LINK. Each of them could potentially refer to a different
network namespace which is confusing and a potential security liability
given that pids might be recycled while the netlink request is served or
the process might do a setns() It also lets us indicate that network namespace
ids are the preferred way of interacting with network namespaces in rtnetlink
requests. The regression potential is quite minimal since the rtnetlink
requests in question either won't allow IFLA_IF_NETNSID requests before 4.16 is
out (RTM_{NEW,SET}LINK) or don't support IFLA_NET_NS_{PID,FD}
(RTM_{DEL,GET}LINK) in the first place.

We obviously cannot prevent users from passing both IFLA_NET_NS_PID and
IFLA_NET_NS_FD since we have supported this somehow for a long time for
a subset of rtnetlink requests. So the check I'm proposing is to only
fail when both IFLA_IF_NETNSID, and IFLA_NET_NS_PID or IFLA_NET_NS_FD are
passed.

Thanks!
Christian

---
ChangeLog v2->v3:
* Specifying target network namespaces with pids or fds seems racy since the
  process might die and the pid get recycled or the process does a setns() in
  which case the tests would be invalid. So only check whether multiple
  properties are specified and report a helpful error in this case.
ChangeLog v1->v2:
* return errno when the specified network namespace id is invalid
* fill in struct netlink_ext_ack if the network namespace id is invalid
* rename rtnl_ensure_unique_netns_attr() to rtnl_ensure_unique_netns() to
  indicate that a request without any network namespace identifying attributes
  is also considered valid.
ChangeLog v0->v1:
* report a descriptive error to userspace via struct netlink_ext_ack
* do not fail when multiple properties specifiy the same network namespace
---

Christian Brauner (1):
  rtnetlink: require unique netns identifier

 net/core/rtnetlink.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

-- 
2.14.1