net: Allow class-e address assignment via ifconfig ioctl

While 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.

While CIDR has been obsolete for 2 decades, and a survey of all the
open source code in the world shows the IN_whatever macros are also
obsolete... rather than obsolete CIDR from this ioctl entirely, this
patch merely enables class-e assignment, sanely.
Signed-off-by: Dave Taht <dave.taht@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/in.h

@@ -266,10 +266,14 @@ struct sockaddr_in {
 
 #define	IN_CLASSD(a)		((((long int) (a)) & 0xf0000000) == 0xe0000000)
 #define	IN_MULTICAST(a)		IN_CLASSD(a)
-#define IN_MULTICAST_NET	0xF0000000
+#define	IN_MULTICAST_NET	0xe0000000
 
-#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)

net/ipv4/devinet.c

@@ -952,17 +952,18 @@ 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);
-
 		if (IN_CLASSA(haddr))
 			rc = 8;
 		else if (IN_CLASSB(haddr))
 			rc = 16;
 		else if (IN_CLASSC(haddr))
 			rc = 24;
+		else if (IN_CLASSE(haddr))
+			rc = 32;
 	}
 
 	return rc;

net/ipv4/ipconfig.c

@@ -429,6 +429,8 @@ 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);