From 46bf067870156abd61fe24d14c2486d15b8b502c Mon Sep 17 00:00:00 2001
From: Dave Taht <dave@taht.net>
Date: Fri, 14 Dec 2018 18:38:40 +0000
Subject: [PATCH 1/1] Allow class-e address assignment in ifconfig and early
 boot

While the linux kernel became mostly "class-e clean" a decade ago,
and most distributions long ago switched to the iproute2 suite
of utilities, which allow class-e (240.0.0.0/4) address assignment,
distributions relying on busybox, toybox and other forms of
ifconfig cannot assign class-e addresses without this kernel patch.

With this patch, also, a boot command line on these addresses is feasible:
(ip=248.0.1.2::248.0.1.1:255.255.255.0).

While CIDR has been obsolete for 2 decades, and a survey of all the
userspace open source code in the world shows most IN_whatever macros
are also obsolete... rather than obsolete CIDR from this ioctl entirely,
this patch merely enables class-e assignment, sanely.

H/T to Vince Fuller and his original patch here:
    https://lkml.org/lkml/2008/1/7/370

Signed-off-by: Dave Taht <dave.taht@gmail.com>
Reviewed-by: John Gilmore <gnu@toad.com>
---
 include/uapi/linux/in.h | 8 ++++++--
 net/ipv4/devinet.c      | 4 +++-
 net/ipv4/ipconfig.c     | 2 ++
 3 files changed, 11 insertions(+), 3 deletions(-)

--- a/include/uapi/linux/in.h
+++ b/include/uapi/linux/in.h
@@ -268,8 +268,12 @@ struct sockaddr_in {
 #define	IN_MULTICAST(a)		IN_CLASSD(a)
 #define IN_MULTICAST_NET	0xF0000000
 
-#define	IN_EXPERIMENTAL(a)	((((long int) (a)) & 0xf0000000) == 0xf0000000)
-#define	IN_BADCLASS(a)		IN_EXPERIMENTAL((a))
+#define	IN_BADCLASS(a)		((((long int) (a) ) == 0xffffffff)
+#define	IN_EXPERIMENTAL(a)	IN_BADCLASS((a))
+
+#define	IN_CLASSE(a)		((((long int) (a)) & 0xf0000000) == 0xf0000000)
+#define	IN_CLASSE_NET		0xffffffff
+#define	IN_CLASSE_NSHIFT	0
 
 /* Address to accept any incoming messages. */
 #define	INADDR_ANY		((unsigned long int) 0x00000000)
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -921,7 +921,7 @@ static int inet_abc_len(__be32 addr)
 {
 	int rc = -1;	/* Something else, probably a multicast. */
 
-	if (ipv4_is_zeronet(addr))
+	if (ipv4_is_zeronet(addr) || ipv4_is_lbcast(addr))
 		rc = 0;
 	else {
 		__u32 haddr = ntohl(addr);
@@ -932,6 +932,8 @@ static int inet_abc_len(__be32 addr)
 			rc = 16;
 		else if (IN_CLASSC(haddr))
 			rc = 24;
+		else if (IN_CLASSE(haddr))
+			rc = 32;
 	}
 
 	return rc;
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -457,6 +457,8 @@ static int __init ic_defaults(void)
 			ic_netmask = htonl(IN_CLASSB_NET);
 		else if (IN_CLASSC(ntohl(ic_myaddr)))
 			ic_netmask = htonl(IN_CLASSC_NET);
+		else if (IN_CLASSE(ntohl(ic_myaddr)))
+			ic_netmask = htonl(IN_CLASSE_NET);
 		else {
 			pr_err("IP-Config: Unable to guess netmask for address %pI4\n",
 			       &ic_myaddr);
