Introduce a facility to generate unpredictable 32 bit numbers with

near maximal (2^32) cycle times. These are useful for network
IDs in cases where there are negative consequences to ID prediction
and/or reuse.

Use the idgen32() functions to generate IPv6 IDs and NFS client/server
XIDs.

Pseudorandom permutation code in crypto/idgen.c based on public
domain skip32.c from Greg Rose.

feedback & ok thib@ deraadt@

1 files changed, 21 insertions, 4 deletions

diff --git a/sys/nfs/krpc_subr.c b/sys/nfs/krpc_subr.c
index 39dfe6ffa59..363a837d985 100644
--- a/sys/nfs/krpc_subr.c
+++ b/sys/nfs/krpc_subr.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: krpc_subr.c,v 1.15 2008/05/23 15:51:12 thib Exp $	*/
+/*	$OpenBSD: krpc_subr.c,v 1.16 2008/06/09 22:47:42 djm Exp $	*/
 /*	$NetBSD: krpc_subr.c,v 1.12.4.1 1996/06/07 00:52:26 cgd Exp $	*/
 
 /*
@@ -61,6 +61,7 @@
 #include <nfs/krpc.h>
 #include <nfs/xdr_subs.h>
 #include <dev/rndvar.h>
+#include <crypto/idgen.h>
 
 /*
  * Kernel support for Sun RPC
@@ -115,6 +116,24 @@ struct rpc_reply {
 
 #define MIN_REPLY_HDR 16	/* xid, dir, astat, errno */
 
+u_int32_t krpc_get_xid(void);
+
+/*
+ * Return an unpredictable XID.
+ */
+u_int32_t
+krpc_get_xid(void)
+{
+	static struct idgen32_ctx krpc_xid_ctx;
+	static int called = 0;
+
+	if (!called) {
+		called = 1;
+		idgen32_init(&krpc_xid_ctx);
+	}
+	return idgen32(&krpc_xid_ctx);
+}
+
 /*
  * What is the longest we will wait before re-sending a request?
  * Note this is also the frequency of "RPC timeout" messages.
@@ -201,7 +220,6 @@ krpc_call(sa, prog, vers, func, data, from_p, retries)
 	struct uio auio;
 	int error, rcvflg, timo, secs, len;
 	static u_int32_t xid = 0;
-	u_int32_t newxid;
 	int *ip;
 	struct timeval *tv;
 
@@ -299,8 +317,7 @@ krpc_call(sa, prog, vers, func, data, from_p, retries)
 	mhead->m_len = sizeof(*call);
 	bzero((caddr_t)call, sizeof(*call));
 	/* rpc_call part */
-	while ((newxid = arc4random()) == xid);
-	xid = newxid;
+	xid = krpc_get_xid();
 	call->rp_xid = txdr_unsigned(xid);
 	/* call->rp_direction = 0; */
 	call->rp_rpcvers = txdr_unsigned(2);