netdev - Re: [PATCH net] net: prevent address overwrite in connect() and sendmsg()

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Date: Thu, 14 Sep 2023 11:41:19 -0700
From: Jordan Rife <jrife@...gle.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>, Daniel Borkmann <daniel@...earbox.net>, 
	davem@...emloft.net, Eric Dumazet <edumazet@...gle.com>, kuba@...nel.org, 
	netdev@...r.kernel.org, dborkman@...nel.org
Subject: Re: [PATCH net] net: prevent address overwrite in connect() and sendmsg()

> 1) Swap out calls to sock->ops->connect() with kernel_connect()

This is trivial, as expected. I have a patch ready that swaps out all
occurrences of sock->ops->connect().

> 2) Move the address copy to kernel_sendmsg()
> 3) Swap out calls to sock_sendmsg()/sock->ops->sendmsg() with kernel_sendmsg()

This turns out to be less trivial. kernel_sensmsg() looks to be a
special case of sock_sendmsg() with sock_sendmsg() being the more
generic of the two:

int kernel_sendmsg(struct socket *sock, struct msghdr *msg,
  struct kvec *vec, size_t num, size_t size)
{
  iov_iter_kvec(&msg->msg_iter, ITER_SOURCE, vec, num, size);
  return sock_sendmsg(sock, msg);
}

It populates msg->msg_iter with a kvec whereas most cases I could find
where sock_sendmsg() is used are using a bio_vec. Some examples:

==drivers/iscsi/iscsi_tcp.c: iscsi_sw_tcp_xmit_segment()==
iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bv, 1, copy);

r = sock_sendmsg(sk, &msg);

==fs/ocfs2/cluster: o2net_sendpage()==
bvec_set_virt(&bv, virt, size);
iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bv, 1, size);

while (1) {
msg.msg_flags = MSG_DONTWAIT | MSG_SPLICE_PAGES;
mutex_lock(&sc->sc_send_lock);
ret = sock_sendmsg(sc->sc_sock, &msg);

==net/sunrpc/svcsock.c: svc_udp_sendto()==
iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec,
count, 0);
err = sock_sendmsg(svsk->sk_sock, &msg);
if (err == -ECONNREFUSED) {
/* ICMP error on earlier request. */
iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec,
count, 0);
err = sock_sendmsg(svsk->sk_sock, &msg);
}

Maybe these two types are more interchangeable than I'm thinking, but
it seems like it might be simpler to just do the address copy inside
sock_sendmsg(). Does this revised plan sound reasonable:

1) Swap out calls to sock->ops->connect() with kernel_connect()
2) Move the address copy to sock_sendmsg()

I also noticed that BPF hooks inside bind() can rewrite the bind
address. Should we do something similar for kernel_bind:

1) Add an address copy to kernel_bind()
2) Swap out direct calls to ops->bind() with kernel_bind()

-Jordan

On Thu, Sep 14, 2023 at 1:24 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On Wed, 2023-09-13 at 10:02 -0400, Willem de Bruijn wrote:
> > On Tue, Sep 12, 2023 at 5:09 PM Jordan Rife <jrife@...gle.com> wrote:
> > >
> > > > If we take this path, it could be a single patch. The subsystem
> > > > maintainers should be CC:ed so that they can (N)ACK it.
> > > >
> > > > But I do not mean to ask to split it up and test each one separately.
> > > >
> > > > The change from sock->ops->connect to kernel_connect is certainly
> > > > trivial enough that compile testing should suffice.
> > >
> > > Ack. Thanks for clarifying.
> > >
> > > > The only question is whether we should pursue your original patch and
> > > > accept that this will continue, or one that improves the situation,
> > > > but touches more files and thus has a higher risk of merge conflicts.
> > > >
> > > > I'd like to give others some time to chime in. I've given my opinion,
> > > > but it's only one.
> > > >
> > > > I'd like to give others some time to chime in. I've given my opinion,
> > > > but it's only one.
> > >
> > > Sounds good. I'll wait to hear others' opinions on the best path forward.
> >
> > No other comments so far.
> >
> > My hunch is that a short list of these changes
> >
> > ```
> > @@ -1328,7 +1328,7 @@ static int kernel_bindconnect(struct socket *s,
> > struct sockaddr *laddr,
> >         if (rv < 0)
> >                 return rv;
> >
> > -       rv = s->ops->connect(s, raddr, size, flags);
> > +       rv = kernel_connect(s, raddr, size, flags);
> > ```
> >
> > is no more invasive than your proposed patch, and gives a more robust outcome.
> >
> > Please take a stab.
>
> I'm sorry for the late feedback. For the records, I agree the cleanest
> fix described above should be attempted first.
>
> Thanks,
>
> Paolo
>