NFSD: If port value written to /proc/fs/nfsd/portlist is invalid, return EINVAL

Make sure port value read from user space by write_ports is valid before
passing it to svc_find_xprt().  If it wasn't, the writer would get ENOENT
instead of EINVAL.
Noticed-by: NJ. Bruce Fields <bfields@fieldses.org>
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfsd/nfsctl.c

@@ -938,6 +938,8 @@ static ssize_t __write_ports(struct file *file, char *buf, size_t size)
 		char transport[16];
 		int port;
 		if (sscanf(buf, "%15s %4d", transport, &port) == 2) {
+			if (port < 1 || port > 65535)
+				return -EINVAL;
 			err = nfsd_create_serv();
 			if (!err) {
 				err = svc_create_xprt(nfsd_serv,
@@ -960,7 +962,7 @@ static ssize_t __write_ports(struct file *file, char *buf, size_t size)
 		char transport[16];
 		int port;
 		if (sscanf(&buf[1], "%15s %4d", transport, &port) == 2) {
-			if (port == 0)
+			if (port < 1 || port > 65535)
 				return -EINVAL;
 			if (nfsd_serv) {
 				xprt = svc_find_xprt(nfsd_serv, transport,