nfs: Permit null requests (aka server pings) from non-reserved ports

Unfortunately, this is recommended by rfc 2623 and used by Linux
nfs-utils to mount NFS exports. So until nfs-utils switches into
using reserved ports, this is needed to mount OpenBSD file-systems
on most (all?) Linux distros.

Bits from claudio, ok millert

sys/nfs/nfs_socket.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: nfs_socket.c,v 1.147 2024/03/31 13:50:00 mvs Exp $	*/
+/*	$OpenBSD: nfs_socket.c,v 1.148 2024/04/19 06:50:37 ratchov Exp $	*/
 /*	$NetBSD: nfs_socket.c,v 1.27 1996/04/15 20:20:00 thorpej Exp $	*/
 
 /*
@@ -1588,7 +1588,7 @@ nfsrv_rcv(struct socket *so, caddr_t arg, int waitflag)
 		 */
 		auio.uio_resid = 1000000000;
 		flags = MSG_DONTWAIT;
-		error = soreceive(so, &nam, &auio, &mp, NULL,
+		error = soreceive(so, NULL, &auio, &mp, NULL,
 		    &flags, 0);
 		if (error || mp == NULL) {
 			if (error == EWOULDBLOCK)
@@ -1626,20 +1626,6 @@ nfsrv_rcv(struct socket *so, caddr_t arg, int waitflag)
 			error = soreceive(so, &nam, &auio, &mp,
 			    NULL, &flags, 0);
 			if (mp) {
-				struct sockaddr_in *sin;
-
-				if (nam == NULL) {
-					nfsstats.srv_errs++;
-					m_freem(mp);
-					continue;
-				}
-				if (in_nam2sin(nam, &sin) != 0 ||
-				    ntohs(sin->sin_port) >= IPPORT_RESERVED) {
-					nfsstats.srv_errs++;
-					m_freem(nam);
-					m_freem(mp);
-					continue;
-				}
 				m = nam;
 				m->m_next = mp;
 				if (slp->ns_recend)

sys/nfs/nfs_syscalls.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: nfs_syscalls.c,v 1.123 2024/03/31 13:50:00 mvs Exp $	*/
+/*	$OpenBSD: nfs_syscalls.c,v 1.124 2024/04/19 06:50:37 ratchov Exp $	*/
 /*	$NetBSD: nfs_syscalls.c,v 1.19 1996/02/18 11:53:52 fvdl Exp $	*/
 
 /*
@@ -251,18 +251,6 @@ nfssvc_addsock(struct file *fp, struct mbuf *mynam)
 		m_freem(mynam);
 		return (EINVAL);
 	}
-	if (mynam != NULL) {
-		struct sockaddr_in *sin;
-		error = in_nam2sin(mynam, &sin);
-		if (error) {
-			m_freem(mynam);
-			return (error);
-		}
-		if (ntohs(sin->sin_port) >= IPPORT_RESERVED) {
-			m_freem(mynam);
-			return (ECONNREFUSED);
-		}
-	}
 
 	if (so->so_type == SOCK_STREAM)
 		siz = NFS_MAXPACKET + sizeof (u_long);
@@ -323,6 +311,18 @@ nfssvc_addsock(struct file *fp, struct mbuf *mynam)
 	return (0);
 }
 
+static inline int nfssvc_checknam(struct mbuf *nam)
+{
+	struct sockaddr_in *sin;
+
+	if (nam == NULL ||
+	    in_nam2sin(nam, &sin) != 0 ||
+	    ntohs(sin->sin_port) >= IPPORT_RESERVED) {
+		return -1;
+	}
+	return 0;
+}
+
 /*
  * Called by nfssvc() for nfsds. Just loops around servicing rpc requests
  * until it is killed by a signal.
@@ -402,6 +402,16 @@ nfssvc_nfsd(struct nfsd *nfsd)
 	cacherep = nfsrv_getcache(nd, slp, &mreq);
 	switch (cacherep) {
 	case RC_DOIT:
+		/*
+		 * Unless this is a null request (server ping), make
+		 * sure that the client is using a reserved source port.
+		 */
+		if (nd->nd_procnum != 0 && nfssvc_checknam(nd->nd_nam) == -1) {
+			/* drop it */
+			m_freem(nd->nd_mrep);
+			m_freem(nd->nd_nam2);
+			break;
+		}
 		error = (*(nfsrv3_procs[nd->nd_procnum]))(nd, slp, nfsd->nfsd_procp, &mreq);
 		if (mreq == NULL) {
 			if (nd != NULL) {