nfs/nfsd/sunrpc: enforce transport requirements for NFSv4

NFSv4 requires a transport "that is specified to avoid network
congestion" (RFC 7530, section 3.1, paragraph 2).  In practical terms,
that means that you should not run NFSv4 over UDP. The server has never
enforced that requirement, however.

This patchset fixes this by adding a new flag to the svc_version that
states that it has these transport requirements. With that, we can check
that the transport has XPT_CONG_CTRL set before processing an RPC. If it
doesn't we reject it with RPC_PROG_MISMATCH.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 85bcdea67a3f..1fc3ff822168 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1169,6 +1169,21 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
           !(versp = progp->pg_vers[vers]))
                 goto err_bad_vers;
 
+        /*
+         * Some protocol versions (namely NFSv4) require some form of
+         * congestion control.  (See RFC 7530 section 3.1 paragraph 2)
+         * In other words, UDP is not allowed. We mark those when setting
+         * up the svc_xprt, and verify that here.
+         *
+         * The spec is not very clear about what error should be returned
+         * when someone tries to access a server that is listening on UDP
+         * for lower versions. RPC_PROG_MISMATCH seems to be the closest
+         * fit.
+         */
+        if (versp->vs_need_cong_ctrl &&
+            !test_bit(XPT_CONG_CTRL, &rqstp->rq_xprt->xpt_flags))
+                goto err_bad_vers;
+
         procp = versp->vs_proc + proc;
         if (proc >= versp->vs_nproc || !procp->pc_func)
                 goto err_bad_proc;