bin/56500: rpc.lockd needs to use reserved ports

[Jonathan Lennox]

After a day or so of untangling how RPC code works, I've worked out a patch.

I'm pretty sure that this patch regains root privileges for the absolute
minimum amount of time necessary to bind to a reserved port.

I've tested this, and it does (along with the patch in kern/56461) allow me
to sucessfully lock files from a Linux server -- and thus to invoke movemail
on my mailspool, and thus to read my mail on my FreeBSD machine, which was
the whole motivation.

--- usr.sbin/rpc.lockd/lock_proc.c.orig	Sat Sep  6 12:48:10 2003
+++ usr.sbin/rpc.lockd/lock_proc.c	Sat Sep  6 13:18:08 2003
@@ -197,6 +197,8 @@
 	const char *netid;
 	struct netconfig *nconf;
 	char host[NI_MAXHOST];
+	uid_t old_euid;
+	int clnt_fd;
 
 	gettimeofday(&time_now, NULL);
 
@@ -270,6 +272,22 @@
 		syslog(LOG_ERR, "Unable to return result to %s", host);
 		return NULL;
 	}
+
+	/* Get the FD of the client, for bindresvport. */ 
+	clnt_control(client, CLGET_FD, &clnt_fd);
+
+	/* Regain root privileges, for bindresvport. */
+	old_euid = geteuid();
+	seteuid(0);
+
+	/*
+	 * Bind the client FD to a reserved port.
+	 * Some NFS servers reject any NLM request from a non-reserved port. 
+	 */ 
+	bindresvport(clnt_fd, NULL);
+
+	/* Drop root privileges again. */
+	seteuid(old_euid);
 
 	/* Success - update the cache entry */
 	clnt_cache_ptr[clnt_cache_next_to_use] = client;