net: Compute protocol sequence numbers and fragment IDs using MD5.

Computers have become a lot faster since we compromised on the
partial MD4 hash which we use currently for performance reasons.

MD5 is a much safer choice, and is inline with both RFC1948 and
other ISS generators (OpenBSD, Solaris, etc.)

Furthermore, only having 24-bits of the sequence number be truly
unpredictable is a very serious limitation.  So the periodic
regeneration and 8-bit counter have been removed.  We compute and
use a full 32-bit sequence number.

For ipv6, DCCP was found to use a 32-bit truncated initial sequence
number (it needs 43-bits) and that is fixed here as well.

Reported-by: Dan Kaminsky <[email protected]>
Tested-by: Willy Tarreau <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

net/ipv4/inet_hashtables.c

@@ -21,6 +21,7 @@
 
 #include <net/inet_connection_sock.h>
 #include <net/inet_hashtables.h>
+#include <net/secure_seq.h>
 #include <net/ip.h>
 
 /*

net/ipv4/inetpeer.c

@@ -19,6 +19,7 @@
 #include <linux/net.h>
 #include <net/ip.h>
 #include <net/inetpeer.h>
+#include <net/secure_seq.h>
 
 /*
  *  Theory of operations.

net/ipv4/netfilter/nf_nat_proto_common.c

@@ -12,6 +12,7 @@
 #include <linux/ip.h>
 
 #include <linux/netfilter.h>
+#include <net/secure_seq.h>
 #include <net/netfilter/nf_nat.h>
 #include <net/netfilter/nf_nat_core.h>
 #include <net/netfilter/nf_nat_rule.h>

net/ipv4/route.c

@@ -109,6 +109,7 @@
 #include <linux/sysctl.h>
 #endif
 #include <net/atmclip.h>
+#include <net/secure_seq.h>
 
 #define RT_FL_TOS(oldflp4) \
     ((u32)(oldflp4->flowi4_tos & (IPTOS_RT_MASK | RTO_ONLINK)))

net/ipv4/tcp_ipv4.c

@@ -72,6 +72,7 @@
 #include <net/timewait_sock.h>
 #include <net/xfrm.h>
 #include <net/netdma.h>
+#include <net/secure_seq.h>
 
 #include <linux/inet.h>
 #include <linux/ipv6.h>