Subject: Re: [PATCH net-next 07/10] sctp: add sockopt to get/set stream scheduler

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Fri, 29 Sep 2017 14:14:15 -0300

On Fri, Sep 29, 2017 at 12:47:32PM -0400, Neil Horman wrote:
> On Thu, Sep 28, 2017 at 05:25:20PM -0300, Marcelo Ricardo Leitner wrote:
> > As defined per RFC Draft ndata Section 4.3.2, named as
> > SCTP_STREAM_SCHEDULER.
> > 
> > See-also: https://tools.ietf.org/html/draft-ietf-tsvwg-sctp-ndata-13
> > Signed-off-by: Marcelo Ricardo Leitner <[email-masked]>
> > ---
> >  include/uapi/linux/sctp.h |  1 +
> >  net/sctp/socket.c         | 75 +++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 76 insertions(+)
> > 
> > diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> > index 4487e7625ddbd48be1868a8292a807ecd0a314bc..0050f10087d224bad87c8c54ad318003381aee12 100644
> > --- a/include/uapi/linux/sctp.h
> > +++ b/include/uapi/linux/sctp.h
> > @@ -122,6 +122,7 @@ typedef __s32 sctp_assoc_t;
> >  #define SCTP_RESET_ASSOC	120
> >  #define SCTP_ADD_STREAMS	121
> >  #define SCTP_SOCKOPT_PEELOFF_FLAGS 122
> > +#define SCTP_STREAM_SCHEDULER	123
> >  
> >  /* PR-SCTP policies */
> >  #define SCTP_PR_SCTP_NONE	0x0000
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index d207734326b085e60625e4333f74221481114892..ae35dbf2810f78c71ce77115ffe4b0e27a672abc 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -79,6 +79,7 @@
> >  #include <net/sock.h>
> >  #include <net/sctp/sctp.h>
> >  #include <net/sctp/sm.h>
> > +#include <net/sctp/stream_sched.h>
> >  
> >  /* Forward declarations for internal helper functions. */
> >  static int sctp_writeable(struct sock *sk);
> > @@ -3914,6 +3915,36 @@ static int sctp_setsockopt_add_streams(struct sock *sk,
> >  	return retval;
> >  }
> >  
> > +static int sctp_setsockopt_scheduler(struct sock *sk,
> > +				     char __user *optval,
> > +				     unsigned int optlen)
> > +{
> > +	struct sctp_association *asoc;
> > +	struct sctp_assoc_value params;
> > +	int retval = -EINVAL;
> > +
> > +	if (optlen < sizeof(params))
> > +		goto out;
> > +
> > +	optlen = sizeof(params);
> > +	if (copy_from_user(&params, optval, optlen)) {
> > +		retval = -EFAULT;
> > +		goto out;
> > +	}
> > +
> > +	if (params.assoc_value > SCTP_SS_MAX)
> > +		goto out;
> > +
> > +	asoc = sctp_id2assoc(sk, params.assoc_id);
> > +	if (!asoc)
> > +		goto out;
> > +
> > +	retval = sctp_sched_set_sched(asoc, params.assoc_value);
> > +
> > +out:
> > +	return retval;
> > +}
> > +
> Don't you want to lock the socket here prior to setting the scheduler, lest you
> race in the set operation after you free the old scheduler and before you init
> the new.  It would seem to me that not doing so can lead to packet loss or
> worse.

Yes. This function is called with the socket already locked:

sctp_setsockopt()
{
...
        lock_sock(sk);

        switch (optname) {
...
        case SCTP_STREAM_SCHEDULER:
                retval = sctp_setsockopt_scheduler(sk, optval, optlen);
                break;
        case SCTP_STREAM_SCHEDULER_VALUE:
                retval = sctp_setsockopt_scheduler_value(sk, optval, optlen);
                break;
...
        release_sock(sk);
...
}

  Marcelo