netdev - Re: [PATCH net] sctp: not allow to set asoc prsctp

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Date:   Thu, 15 Nov 2018 20:25:36 -0200
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Neil Horman <nhorman@...driver.com>
Cc:     Xin Long <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>,
        linux-sctp@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH net] sctp: not allow to set asoc prsctp_enable by sockopt

On Thu, Nov 15, 2018 at 04:43:10PM -0500, Neil Horman wrote:
> On Thu, Nov 15, 2018 at 03:22:21PM -0200, Marcelo Ricardo Leitner wrote:
> > On Thu, Nov 15, 2018 at 07:14:28PM +0800, Xin Long wrote:
> > > As rfc7496#section4.5 says about SCTP_PR_SUPPORTED:
> > > 
> > >    This socket option allows the enabling or disabling of the
> > >    negotiation of PR-SCTP support for future associations.  For existing
> > >    associations, it allows one to query whether or not PR-SCTP support
> > >    was negotiated on a particular association.
> > > 
> > > It means only sctp sock's prsctp_enable can be set.
> > > 
> > > Note that for the limitation of SCTP_{CURRENT|ALL}_ASSOC, we will
> > > add it when introducing SCTP_{FUTURE|CURRENT|ALL}_ASSOC for linux
> > > sctp in another patchset.
> > > 
> > > Fixes: 28aa4c26fce2 ("sctp: add SCTP_PR_SUPPORTED on sctp sockopt")
> > > Reported-by: Ying Xu <yinxu@...hat.com>
> > > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > > ---
> > >  net/sctp/socket.c | 13 +++----------
> > >  1 file changed, 3 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > > index 739f3e5..e9b8232 100644
> > > --- a/net/sctp/socket.c
> > > +++ b/net/sctp/socket.c
> > > @@ -3940,7 +3940,6 @@ static int sctp_setsockopt_pr_supported(struct sock *sk,
> > >  					unsigned int optlen)
> > >  {
> > >  	struct sctp_assoc_value params;
> > > -	struct sctp_association *asoc;
> > >  	int retval = -EINVAL;
> > >  
> > >  	if (optlen != sizeof(params))
> > > @@ -3951,16 +3950,10 @@ static int sctp_setsockopt_pr_supported(struct sock *sk,
> > >  		goto out;
> > >  	}
> > >  
> > > -	asoc = sctp_id2assoc(sk, params.assoc_id);
> > > -	if (asoc) {
> > > -		asoc->prsctp_enable = !!params.assoc_value;
> > > -	} else if (!params.assoc_id) {
> > > -		struct sctp_sock *sp = sctp_sk(sk);
> > > -
> > > -		sp->ep->prsctp_enable = !!params.assoc_value;
> > > -	} else {
> > > +	if (sctp_style(sk, UDP) && sctp_id2assoc(sk, params.assoc_id))
> > 
> > This would allow using a non-existent assoc id on UDP-style sockets to
> > set it at the socket, which is not expected. It should be more like:
> > 
> > +	if (sctp_style(sk, UDP) && params.assoc_id)
> How do you see that to be the case? sctp_id2assoc will return NULL if an
> association isn't found, so the use of sctp_id2assoc should work just fine.

Right, it will return NULL, and because of that it won't bail out as
it should and will adjust the socket config instead.

> Just checking params.assoc_id would instead fail the setting of any association
> id that isn't 0, which I don't think is what we want at all.

I think it is.

For exisitng associations, we can't set this anymore because it was
already negotiated on the handshake
(sctp_process_ext_param()/SCTP_CID_FWD_TSN) and there is no way back
after it. 
For non-existing assocs, they will always inherit it from the socket
value.

Question then is which semantics we want on validating the parameter
here. We have cases such as in sctp_setsockopt_delayed_ack() on which
it will reject using invalid asoc_ids as a way to mean the socket
itself for UDP-style sockets:

        asoc = sctp_id2assoc(sk, params.sack_assoc_id);
        if (!asoc && params.sack_assoc_id && sctp_style(sk, UDP))
                return -EINVAL;

As we are returning the same error for both situations(invalid assoc id
and setting it on existing asoc), we don't need the asoc pointer
itself and can avoid sctp_id2assoc() call, leading to the if() I
suggested.

  Marcelo

> 
> Neil
> 
> > 
> > >  		goto out;
> > > -	}
> > > +
> > > +	sctp_sk(sk)->ep->prsctp_enable = !!params.assoc_value;
> > >  
> > >  	retval = 0;
> > >  
> > > -- 
> > > 2.1.0
> > > 
> >