[PATCHv2 net] sctp: not allow to set asoc prsctp_enable by sockopt

[Xin Long]

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.

v1->v2:
  - drop the params.assoc_id check as Neil suggested.

Fixes: 28aa4c26fce2 ("sctp: add SCTP_PR_SUPPORTED on sctp sockopt")
Reported-by: Ying Xu <yi...@redhat.com>
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/sctp/socket.c | 26 +++++---------------------
 1 file changed, 5 insertions(+), 21 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 739f3e5..bf618d1 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3940,32 +3940,16 @@ 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))
-               goto out;
-
-       if (copy_from_user(&params, optval, optlen)) {
-               retval = -EFAULT;
-               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);
+               return -EINVAL;
 
-               sp->ep->prsctp_enable = !!params.assoc_value;
-       } else {
-               goto out;
-       }
+       if (copy_from_user(&params, optval, optlen))
+               return -EFAULT;
 
-       retval = 0;
+       sctp_sk(sk)->ep->prsctp_enable = !!params.assoc_value;
 
-out:
-       return retval;
+       return 0;
 }
 
 static int sctp_setsockopt_default_prinfo(struct sock *sk,
-- 
2.1.0