RDS: make message size limit compliant with spec

RDS support max message size as 1M but the code doesn't check this
in all cases. Patch fixes it for RDMA & non-RDMA and RDS MR size
and its enforced irrespective of underlying transport.

Signed-off-by: Avinash Repaka <avinash.repaka@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>

net/rds/rdma.c

@@ -40,7 +40,6 @@
 /*
  * XXX
  *  - build with sparse
- *  - should we limit the size of a mr region?  let transport return failure?
  *  - should we detect duplicate keys on a socket?  hmm.
  *  - an rdma is an mlock, apply rlimit?
  */
@@ -200,6 +199,14 @@ static int __rds_rdma_map(struct rds_sock *rs, struct rds_get_mr_args *args,
 		goto out;
 	}
 
+	/* Restrict the size of mr irrespective of underlying transport
+	 * To account for unaligned mr regions, subtract one from nr_pages
+	 */
+	if ((nr_pages - 1) > (RDS_MAX_MSG_SIZE >> PAGE_SHIFT)) {
+		ret = -EMSGSIZE;
+		goto out;
+	}
+
 	rdsdebug("RDS: get_mr addr %llx len %llu nr_pages %u\n",
 		args->vec.addr, args->vec.bytes, nr_pages);