Re: [PATCH net] sunrpc: fix one UAF issue caused by sunrpc kernel tcp socket

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Trond Myklebust <trondmy@hammerspace.com>
Date: Sat, 26 Oct 2024 00:35:30 +0000
> On Fri, 2024-10-25 at 14:20 -0700, Kuniyuki Iwashima wrote:
> > From: "liujian (CE)" <liujian56@huawei.com>
> > Date: Fri, 25 Oct 2024 11:32:52 +0800
> > > > > > If not, then what prevents it from happening?
> > > > > The socket created by the userspace program obtains the
> > > > > reference
> > > > > counting of the namespace, but the kernel socket does not.
> > > > > 
> > > > > There's some discussion here:
> > > > > https://lore.kernel.org/all/CANn89iJE5anTbyLJ0TdGAqGsE+GichY3YzQECjNUVMz=G3bcQg@mail.gmail.com/
> > > > OK... So then it looks to me as if NFS, SMB, AFS, and any other
> > > > networked filesystem that can be started from inside a container
> > > > is
> > > > going to need to do the same thing that rds appears to be doing.
> > 
> > FWIW, recently we saw a similar UAF on CIFS.
> > 
> > 
> > > > 
> > > > Should there perhaps be a helper function in the networking layer
> > > > for
> > > > this?
> > > 
> > > There should be no such helper function at present, right?.
> > > 
> > > If get net's reference to fix this problem, the following test is 
> > > performed. There's nothing wrong with this case. I don't know if
> > > there's 
> > > anything else to consider.
> > > 
> > > I don't have any other ideas other than these two methods. Do you
> > > have 
> > > any suggestions on this problem? @Eric @Jakub ... @All
> > 
> > The netns lifetime should be managed by the upper layer rather than
> > the networking layer.  If the netns is already dead, the upper layer
> > must discard the net pointer anyway.
> > 
> > I suggest checking maybe_get_net() in NFS, CIFS, etc and then calling
> > __sock_create() with kern 0.
> > 
> 
> Thanks for the suggestion, but we already manage the netns lifetime in
> the RPC layer. A reference is taken when the filesystem is being
> mounted. It is dropped when the filesystem is being unmounted.
> 
> The problem is the TCP timer races on shutdown. There is no interest in
> having to manage that in the RPC layer.

Does that mean netns is always alive when the socket is created
in svc_create_socket() or xs_create_sock() ?  If so, you can just
use __sock_create(kern=0) there to prevent net from being freed
before the socket.

sock_create_kern() and kern@ are confusing, and we had similar issues
in other kernel TCP socket users SMC/RDS, so I'll rename them to
sock_create_noref() and no_net_ref@ or something.