Code: __u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
				 __be16 sport, __be16 dport)
{
	__u32 seq;
	__u32 hash[4];
	struct keydata *keyptr = get_keyptr();
	/*
	 *  Pick a unique starting offset for each TCP connection endpoints
	 *  (saddr, daddr, sport, dport).
	 *  Note that the words are placed into the starting vector, which is
	 *  then mixed with a partial MD4 over random data.
	 */
	hash[0] = (__force u32)saddr;
	hash[1] = (__force u32)daddr;
	hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
	hash[3] = keyptr->secret[11];
	seq = half_md4_transform(hash, keyptr->secret) & HASH_MASK;
	seq += keyptr->count;
	/*
	 *	As close as possible to RFC 793, which
	 *	suggests using a 250 kHz clock.
	 *	Further reading shows this assumes 2 Mb/s networks.
	 *	For 10 Mb/s Ethernet, a 1 MHz clock is appropriate.
	 *	For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but
	 *	we also need to limit the resolution so that the u32 seq
	 *	overlaps less than one time per MSL (2 minutes).
	 *	Choosing a clock of 64 ns period is OK. (period of 274 s)
	 */
	seq += ktime_to_ns(ktime_get_real()) >> 6;
	return seq;
}

Vulnerability Type: DoS 
CWE ID: 
Summary: The (1) IPv4 and (2) IPv6 implementations in the Linux kernel before 3.1 use a modified MD4 algorithm to generate sequence numbers and Fragment Identification values, which makes it easier for remote attackers to cause a denial of service (disrupted networking) or hijack network sessions by predicting these values and sending crafted packets.
Commit Message: 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 <dan@doxpara.com>
Tested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>