Date:   Mon, 19 Nov 2018 02:14:50 -0200
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     Neil Horman <nhorman@...driver.com>,
        network dev <netdev@...r.kernel.org>,
        linux-sctp@...r.kernel.org, davem <davem@...emloft.net>
Subject: Re: [PATCH net] sctp: not allow to set asoc prsctp_enable by sockopt

On Sun, Nov 18, 2018 at 04:02:25PM +0900, Xin Long wrote:
> On Sat, Nov 17, 2018 at 12:12 AM Neil Horman <nhorman@...driver.com> wrote:
> >
> > On Thu, Nov 15, 2018 at 09:41:01PM -0200, Marcelo Ricardo Leitner wrote:
> > > [ re-sending, without html this time ]
> > >
> > > On Thu, Nov 15, 2018, 15:26 Neil Horman <nhorman@...driver.com wrote:
> > >
> > > > On Thu, Nov 15, 2018 at 08:25:36PM -0200, Marcelo Ricardo Leitner wrote:
> > > > > 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.
> > > > >
> > > >
> > > > Oh, duh, you're absolutely right, NULL will evalutate to false there, and
> > > > skip
> > > > the conditional goto out;
> > > >
> > > > that said, It would make more sense to me to just change the sense of the
> > > > second
> > > > condition to !sctp_id2assoc(sk, params.assoc_id), so that we goto out if no
> > > > association is found.  it still seems a
> > >
> > >
> > > That would break setting it on the socket without an assoc so far.
> > >
> > ok, yes, I see what xin is getting at now.  The RFC indicates that the
> > setsockopt method for this socket option is meant to set the prsctp enabled
> > value on _future_ associations, implying that we should not operate at all on
> > already existing associations (i.e. we should ignore the assoc_id in the passed
> > in structure and only operate on the socket).  That said, heres the entire text
> > of the RFC section:
> >
> > 4.5.  Socket Option for Getting and Setting the PR-SCTP Support
> >       (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.
> >
> >    Whether or not PR-SCTP is enabled by default is implementation
> >    specific.
> >
> >    This socket option uses IPPROTO_SCTP as its level and
> >    SCTP_PR_SUPPORTED as its name.  It can be used with getsockopt() and
> >    setsockopt().  The socket option value uses the following structure
> >    defined in [RFC6458]:
> >
> >    struct sctp_assoc_value {
> >      sctp_assoc_t assoc_id;
> >      uint32_t assoc_value;
> >    };
> >
> >    assoc_id:  This parameter is ignored for one-to-one style sockets.
> >       For one-to-many style sockets, this parameter indicates upon which
> >       association the user is performing an action.  The special
> >       sctp_assoc_t SCTP_FUTURE_ASSOC can also be used; it is an error to
> >       use SCTP_{CURRENT|ALL}_ASSOC in assoc_id.
> >
> >    assoc_value:  A non-zero value encodes the enabling of PR-SCTP,
> >       whereas a value of 0 encodes the disabling of PR-SCTP.
> >
> >    sctp_opt_info() needs to be extended to support SCTP_PR_SUPPORTED
> >
> > My read of this suggests that for setting the prsctp_enabled flag, we only need
> > a valid socket (the presence or lack of associations is irrelevant), its only
> > for the getsockopt method that we need to specify an assoc_id, as the getsockopt
> > method operates on associations, while the setsockopt method operates at the
> > socket level (to be inherited as association init).
> >
> > Given that, I'd argue that we can skip the check entirely, and just assign
> > sctp_sock(sk)->prsctp_enabled = !!param.assoc_value
> >
> > directly.
> RFC seems to have no clear demands for this, I will just drop the check
> in this patch, thanks.

RFC may not have clear demands, but I still don't see a reason for not
rejecting bogus arguments that can potentially lead to confusion.
We usually do argument parsing in the other way around: restrict as
much as possible, and relax when needed. That avoids applications to
build bad behaviors that we would end up having to cope with it.
Anyhow, I won't oppose to this any further.

@Dave: please give me till Tue to review the other patches. I'm
traveling and will be offline till Mon night. Thanks.

  Marcelo

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