Re: Leaking path or inconsistency LSM checking observed in fs/net

[Stephen Smalley]

On 09/25/2018 07:36 PM, TongZhang wrote:
> ocfs2 is using sock_create instead of sock_create_kern in kernel v4.18.5.
>
> fs/ocfs2/cluster/tcp.c: 1636
> https://elixir.bootlin.com/linux/v4.18.5/source/fs/ocfs2/cluster/tcp.c#L1636
> > ret = sock_create(PF_INET, SOCK_STREAM, IPPROTO_TCP, &sock);
>
> fs/ocfs2/cluster/tcp.c: 2035
> https://elixir.bootlin.com/linux/v4.18.5/source/fs/ocfs2/cluster/tcp.c#L2035
> > ret = sock_create(PF_INET, SOCK_STREAM, IPPROTO_TCP, &sock);

Yes, I think that's the real bug here.  Unless the socket is in fact 
exposed for direct use by userspace, it ought to be using 
sock_create_kern() or similar.  I would suggest that you verify that the 
socket is never returned to userspace, and then submit a patch switching 
the code to using sock_create_kern().

> > On Sep 25, 2018, at 2:44 PM, Stephen Smalley <sds@xxxxxxxxxxxxx> wrote:
> >
> > On 09/25/2018 01:27 PM, Tong Zhang wrote:
> > > Kernel Version: 4.18.5
> > > Problem Description:
> > > We found several leaking path or inconsistency LSM design issue in fs/net.
> > > Currently we can only observe sock creation from kernel and all bind/listen/connect are not sent to LSM.
> > > So, we think that those net/socket related stuff should all go through LSM check and being audited
> > > even it is not a user thread or process.
> > > Hereâs an example where we have a check:
> > > in fs/ocfs2/cluster/tcp.c:2035 o2net_open_listening_sock() a sock is created using sock_create(),
> > > where a LSM check security_socket_create is called(net/socket.c:1242)
> > > And where we donât have a check
> > > fs/ocfs2/cluster/tcp.c:2052 bind
> > > fs/ocfs2/cluster/tcp.c:2059 listen
> > > fs/dlm/lowcomms.c:1264 bind
> > > fs/dlm/lowcomms.c:1278 listen
> > > fs/dlm/lowcomms.c:1354 listen
> > > several places that use kernel_bind/kernel_listen/kernel_connect
> > > net/socket.c:3231 kernel_bind
> > > net/socket.c:3237 kernel_listen
> > > net/socket.c:3286 kernel_connect
> >
> > That's intentional.  LSM isn't trying to mediate kernel-internal operations, and we do not want to apply permission checks against the credentials of the current userspace process for such operations.  ocfs2 should likely be using sock_create_kern.