Commit 6e5714ea authored by David S. Miller's avatar David S. Miller
Browse files

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: default avatarDan Kaminsky <dan@doxpara.com>
Tested-by: default avatarWilly Tarreau <w@1wt.eu>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent bc0b96b5

drivers/char/random.c

+8 −341
Original line number Diff line number Diff line
@@ -1300,345 +1300,14 @@ ctl_table random_table[] = { 
};

#endif 	/* CONFIG_SYSCTL */



/********************************************************************

 *

 * Random functions for networking

 *

 ********************************************************************/



/*

 * TCP initial sequence number picking.  This uses the random number

 * generator to pick an initial secret value.  This value is hashed

 * along with the TCP endpoint information to provide a unique

 * starting point for each pair of TCP endpoints.  This defeats

 * attacks which rely on guessing the initial TCP sequence number.

 * This algorithm was suggested by Steve Bellovin.

 *

 * Using a very strong hash was taking an appreciable amount of the total

 * TCP connection establishment time, so this is a weaker hash,

 * compensated for by changing the secret periodically.

 */



/* F, G and H are basic MD4 functions: selection, majority, parity */

#define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))

#define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))

#define H(x, y, z) ((x) ^ (y) ^ (z))



/*

 * The generic round function.  The application is so specific that

 * we don't bother protecting all the arguments with parens, as is generally

 * good macro practice, in favor of extra legibility.

 * Rotation is separate from addition to prevent recomputation

 */

#define ROUND(f, a, b, c, d, x, s)	\

	(a += f(b, c, d) + x, a = (a << s) | (a >> (32 - s)))

#define K1 0

#define K2 013240474631UL

#define K3 015666365641UL



#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)



static __u32 twothirdsMD4Transform(__u32 const buf[4], __u32 const in[12])

{

	__u32 a = buf[0], b = buf[1], c = buf[2], d = buf[3];



	/* Round 1 */

	ROUND(F, a, b, c, d, in[ 0] + K1,  3);

	ROUND(F, d, a, b, c, in[ 1] + K1,  7);

	ROUND(F, c, d, a, b, in[ 2] + K1, 11);

	ROUND(F, b, c, d, a, in[ 3] + K1, 19);

	ROUND(F, a, b, c, d, in[ 4] + K1,  3);

	ROUND(F, d, a, b, c, in[ 5] + K1,  7);

	ROUND(F, c, d, a, b, in[ 6] + K1, 11);

	ROUND(F, b, c, d, a, in[ 7] + K1, 19);

	ROUND(F, a, b, c, d, in[ 8] + K1,  3);

	ROUND(F, d, a, b, c, in[ 9] + K1,  7);

	ROUND(F, c, d, a, b, in[10] + K1, 11);

	ROUND(F, b, c, d, a, in[11] + K1, 19);



	/* Round 2 */

	ROUND(G, a, b, c, d, in[ 1] + K2,  3);

	ROUND(G, d, a, b, c, in[ 3] + K2,  5);

	ROUND(G, c, d, a, b, in[ 5] + K2,  9);

	ROUND(G, b, c, d, a, in[ 7] + K2, 13);

	ROUND(G, a, b, c, d, in[ 9] + K2,  3);

	ROUND(G, d, a, b, c, in[11] + K2,  5);

	ROUND(G, c, d, a, b, in[ 0] + K2,  9);

	ROUND(G, b, c, d, a, in[ 2] + K2, 13);

	ROUND(G, a, b, c, d, in[ 4] + K2,  3);

	ROUND(G, d, a, b, c, in[ 6] + K2,  5);

	ROUND(G, c, d, a, b, in[ 8] + K2,  9);

	ROUND(G, b, c, d, a, in[10] + K2, 13);



	/* Round 3 */

	ROUND(H, a, b, c, d, in[ 3] + K3,  3);

	ROUND(H, d, a, b, c, in[ 7] + K3,  9);

	ROUND(H, c, d, a, b, in[11] + K3, 11);

	ROUND(H, b, c, d, a, in[ 2] + K3, 15);

	ROUND(H, a, b, c, d, in[ 6] + K3,  3);

	ROUND(H, d, a, b, c, in[10] + K3,  9);

	ROUND(H, c, d, a, b, in[ 1] + K3, 11);

	ROUND(H, b, c, d, a, in[ 5] + K3, 15);

	ROUND(H, a, b, c, d, in[ 9] + K3,  3);

	ROUND(H, d, a, b, c, in[ 0] + K3,  9);

	ROUND(H, c, d, a, b, in[ 4] + K3, 11);

	ROUND(H, b, c, d, a, in[ 8] + K3, 15);



	return buf[1] + b; /* "most hashed" word */

	/* Alternative: return sum of all words? */

}

#endif



#undef ROUND

#undef F

#undef G

#undef H

#undef K1

#undef K2

#undef K3



/* This should not be decreased so low that ISNs wrap too fast. */

#define REKEY_INTERVAL (300 * HZ)

/*

 * Bit layout of the tcp sequence numbers (before adding current time):

 * bit 24-31: increased after every key exchange

 * bit 0-23: hash(source,dest)

 *

 * The implementation is similar to the algorithm described

 * in the Appendix of RFC 1185, except that

 * - it uses a 1 MHz clock instead of a 250 kHz clock

 * - it performs a rekey every 5 minutes, which is equivalent

 * 	to a (source,dest) tulple dependent forward jump of the

 * 	clock by 0..2^(HASH_BITS+1)

 *

 * Thus the average ISN wraparound time is 68 minutes instead of

 * 4.55 hours.

 *

 * SMP cleanup and lock avoidance with poor man's RCU.

 * 			Manfred Spraul <manfred@colorfullife.com>

 *

 */

#define COUNT_BITS 8

#define COUNT_MASK ((1 << COUNT_BITS) - 1)

#define HASH_BITS 24

#define HASH_MASK ((1 << HASH_BITS) - 1)

static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;



static struct keydata {

	__u32 count; /* already shifted to the final position */

	__u32 secret[12];

} ____cacheline_aligned ip_keydata[2];



static unsigned int ip_cnt;



static void rekey_seq_generator(struct work_struct *work);



static DECLARE_DELAYED_WORK(rekey_work, rekey_seq_generator);



/*

 * Lock avoidance:

 * The ISN generation runs lockless - it's just a hash over random data.

 * State changes happen every 5 minutes when the random key is replaced.

 * Synchronization is performed by having two copies of the hash function

 * state and rekey_seq_generator always updates the inactive copy.

 * The copy is then activated by updating ip_cnt.

 * The implementation breaks down if someone blocks the thread

 * that processes SYN requests for more than 5 minutes. Should never

 * happen, and even if that happens only a not perfectly compliant

 * ISN is generated, nothing fatal.

 */

static void rekey_seq_generator(struct work_struct *work)

static int __init random_int_secret_init(void)

{

	struct keydata *keyptr = &ip_keydata[1 ^ (ip_cnt & 1)];



	get_random_bytes(keyptr->secret, sizeof(keyptr->secret));

	keyptr->count = (ip_cnt & COUNT_MASK) << HASH_BITS;

	smp_wmb();

	ip_cnt++;

	schedule_delayed_work(&rekey_work,

			      round_jiffies_relative(REKEY_INTERVAL));

}



static inline struct keydata *get_keyptr(void)

{

	struct keydata *keyptr = &ip_keydata[ip_cnt & 1];



	smp_rmb();



	return keyptr;

}



static __init int seqgen_init(void)

{

	rekey_seq_generator(NULL);

	get_random_bytes(random_int_secret, sizeof(random_int_secret));

	return 0;

}

late_initcall(seqgen_init);



#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)

__u32 secure_tcpv6_sequence_number(__be32 *saddr, __be32 *daddr,

				   __be16 sport, __be16 dport)

{

	__u32 seq;

	__u32 hash[12];

	struct keydata *keyptr = get_keyptr();



	/* The procedure is the same as for IPv4, but addresses are longer.

	 * Thus we must use twothirdsMD4Transform.

	 */



	memcpy(hash, saddr, 16);

	hash[4] = ((__force u16)sport << 16) + (__force u16)dport;

	memcpy(&hash[5], keyptr->secret, sizeof(__u32) * 7);



	seq = twothirdsMD4Transform((const __u32 *)daddr, hash) & HASH_MASK;

	seq += keyptr->count;



	seq += ktime_to_ns(ktime_get_real());



	return seq;

}

EXPORT_SYMBOL(secure_tcpv6_sequence_number);

#endif



/*  The code below is shamelessly stolen from secure_tcp_sequence_number().

 *  All blames to Andrey V. Savochkin <saw@msu.ru>.

 */

__u32 secure_ip_id(__be32 daddr)

{

	struct keydata *keyptr;

	__u32 hash[4];



	keyptr = get_keyptr();



	/*

	 *  Pick a unique starting offset for each IP destination.

	 *  The dest ip address is placed in the starting vector,

	 *  which is then hashed with random data.

	 */

	hash[0] = (__force __u32)daddr;

	hash[1] = keyptr->secret[9];

	hash[2] = keyptr->secret[10];

	hash[3] = keyptr->secret[11];



	return half_md4_transform(hash, keyptr->secret);

}



__u32 secure_ipv6_id(const __be32 daddr[4])

{

	const struct keydata *keyptr;

	__u32 hash[4];



	keyptr = get_keyptr();



	hash[0] = (__force __u32)daddr[0];

	hash[1] = (__force __u32)daddr[1];

	hash[2] = (__force __u32)daddr[2];

	hash[3] = (__force __u32)daddr[3];



	return half_md4_transform(hash, keyptr->secret);

}



#ifdef CONFIG_INET



__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;

}



/* Generate secure starting point for ephemeral IPV4 transport port search */

u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)

{

	struct keydata *keyptr = get_keyptr();

	u32 hash[4];



	/*

	 *  Pick a unique starting offset for each ephemeral port search

	 *  (saddr, daddr, dport) and 48bits of random data.

	 */

	hash[0] = (__force u32)saddr;

	hash[1] = (__force u32)daddr;

	hash[2] = (__force u32)dport ^ keyptr->secret[10];

	hash[3] = keyptr->secret[11];



	return half_md4_transform(hash, keyptr->secret);

}

EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);



#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)

u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,

			       __be16 dport)

{

	struct keydata *keyptr = get_keyptr();

	u32 hash[12];



	memcpy(hash, saddr, 16);

	hash[4] = (__force u32)dport;

	memcpy(&hash[5], keyptr->secret, sizeof(__u32) * 7);



	return twothirdsMD4Transform((const __u32 *)daddr, hash);

}

#endif



#if defined(CONFIG_IP_DCCP) || defined(CONFIG_IP_DCCP_MODULE)

/* Similar to secure_tcp_sequence_number but generate a 48 bit value

 * bit's 32-47 increase every key exchange

 *       0-31  hash(source, dest)

 */

u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,

				__be16 sport, __be16 dport)

{

	u64 seq;

	__u32 hash[4];

	struct keydata *keyptr = get_keyptr();



	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);

	seq |= ((u64)keyptr->count) << (32 - HASH_BITS);



	seq += ktime_to_ns(ktime_get_real());

	seq &= (1ull << 48) - 1;



	return seq;

}

EXPORT_SYMBOL(secure_dccp_sequence_number);

#endif



#endif /* CONFIG_INET */



late_initcall(random_int_secret_init);



/*

 * Get a random word for internal kernel use only. Similar to urandom but
@@ -1646,17 +1315,15 @@ EXPORT_SYMBOL(secure_dccp_sequence_number); 
 * value is not cryptographically secure but for several uses the cost of

 * depleting entropy is too high

 */

DEFINE_PER_CPU(__u32 [4], get_random_int_hash);

DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash);

unsigned int get_random_int(void)

{

	struct keydata *keyptr;

	__u32 *hash = get_cpu_var(get_random_int_hash);

	int ret;

	unsigned int ret;



	keyptr = get_keyptr();

	hash[0] += current->pid + jiffies + get_cycles();



	ret = half_md4_transform(hash, keyptr->secret);

	md5_transform(hash, random_int_secret);

	ret = hash[0];

	put_cpu_var(get_random_int_hash);



	return ret;

include/linux/random.h

+0 −12
Original line number Diff line number Diff line
@@ -57,18 +57,6 @@ extern void add_interrupt_randomness(int irq); 
extern void get_random_bytes(void *buf, int nbytes);

void generate_random_uuid(unsigned char uuid_out[16]);



extern __u32 secure_ip_id(__be32 daddr);

extern __u32 secure_ipv6_id(const __be32 daddr[4]);

extern u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport);

extern u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,

				      __be16 dport);

extern __u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,

					__be16 sport, __be16 dport);

extern __u32 secure_tcpv6_sequence_number(__be32 *saddr, __be32 *daddr,

					  __be16 sport, __be16 dport);

extern u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,

				       __be16 sport, __be16 dport);



#ifndef MODULE

extern const struct file_operations random_fops, urandom_fops;

#endif

include/net/secure_seq.h

0 → 100644
+20 −0
Original line number Diff line number Diff line 
#ifndef _NET_SECURE_SEQ

#define _NET_SECURE_SEQ



#include <linux/types.h>



extern __u32 secure_ip_id(__be32 daddr);

extern __u32 secure_ipv6_id(const __be32 daddr[4]);

extern u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport);

extern u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,

				      __be16 dport);

extern __u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,

					__be16 sport, __be16 dport);

extern __u32 secure_tcpv6_sequence_number(__be32 *saddr, __be32 *daddr,

					  __be16 sport, __be16 dport);

extern u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,

				       __be16 sport, __be16 dport);

extern u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,

					 __be16 sport, __be16 dport);



#endif /* _NET_SECURE_SEQ */

net/core/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -3,7 +3,7 @@ 
#



obj-y := sock.o request_sock.o skbuff.o iovec.o datagram.o stream.o scm.o \

	 gen_stats.o gen_estimator.o net_namespace.o

	 gen_stats.o gen_estimator.o net_namespace.o secure_seq.o



obj-$(CONFIG_SYSCTL) += sysctl_net_core.o

net/core/secure_seq.c

0 → 100644
+184 −0
Original line number Diff line number Diff line 
#include <linux/kernel.h>

#include <linux/init.h>

#include <linux/cryptohash.h>

#include <linux/module.h>

#include <linux/cache.h>

#include <linux/random.h>

#include <linux/hrtimer.h>

#include <linux/ktime.h>

#include <linux/string.h>



#include <net/secure_seq.h>



static u32 net_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;



static int __init net_secret_init(void)

{

	get_random_bytes(net_secret, sizeof(net_secret));

	return 0;

}

late_initcall(net_secret_init);



static u32 seq_scale(u32 seq)

{

	/*

	 *	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)

	 */

	return seq + (ktime_to_ns(ktime_get_real()) >> 6);

}



#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)

__u32 secure_tcpv6_sequence_number(__be32 *saddr, __be32 *daddr,

				   __be16 sport, __be16 dport)

{

	u32 secret[MD5_MESSAGE_BYTES / 4];

	u32 hash[MD5_DIGEST_WORDS];

	u32 i;



	memcpy(hash, saddr, 16);

	for (i = 0; i < 4; i++)

		secret[i] = net_secret[i] + daddr[i];

	secret[4] = net_secret[4] +

		(((__force u16)sport << 16) + (__force u16)dport);

	for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)

		secret[i] = net_secret[i];



	md5_transform(hash, secret);



	return seq_scale(hash[0]);

}

EXPORT_SYMBOL(secure_tcpv6_sequence_number);



u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,

			       __be16 dport)

{

	u32 secret[MD5_MESSAGE_BYTES / 4];

	u32 hash[MD5_DIGEST_WORDS];

	u32 i;



	memcpy(hash, saddr, 16);

	for (i = 0; i < 4; i++)

		secret[i] = net_secret[i] + (__force u32) daddr[i];

	secret[4] = net_secret[4] + (__force u32)dport;

	for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)

		secret[i] = net_secret[i];



	md5_transform(hash, secret);



	return hash[0];

}

#endif



#ifdef CONFIG_INET

__u32 secure_ip_id(__be32 daddr)

{

	u32 hash[MD5_DIGEST_WORDS];



	hash[0] = (__force __u32) daddr;

	hash[1] = net_secret[13];

	hash[2] = net_secret[14];

	hash[3] = net_secret[15];



	md5_transform(hash, net_secret);



	return hash[0];

}



__u32 secure_ipv6_id(const __be32 daddr[4])

{

	__u32 hash[4];



	memcpy(hash, daddr, 16);

	md5_transform(hash, net_secret);



	return hash[0];

}



__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,

				 __be16 sport, __be16 dport)

{

	u32 hash[MD5_DIGEST_WORDS];



	hash[0] = (__force u32)saddr;

	hash[1] = (__force u32)daddr;

	hash[2] = ((__force u16)sport << 16) + (__force u16)dport;

	hash[3] = net_secret[15];



	md5_transform(hash, net_secret);



	return seq_scale(hash[0]);

}



u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)

{

	u32 hash[MD5_DIGEST_WORDS];



	hash[0] = (__force u32)saddr;

	hash[1] = (__force u32)daddr;

	hash[2] = (__force u32)dport ^ net_secret[14];

	hash[3] = net_secret[15];



	md5_transform(hash, net_secret);



	return hash[0];

}

EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);

#endif



#if defined(CONFIG_IP_DCCP) || defined(CONFIG_IP_DCCP_MODULE)

u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,

				__be16 sport, __be16 dport)

{

	u32 hash[MD5_DIGEST_WORDS];

	u64 seq;



	hash[0] = (__force u32)saddr;

	hash[1] = (__force u32)daddr;

	hash[2] = ((__force u16)sport << 16) + (__force u16)dport;

	hash[3] = net_secret[15];



	md5_transform(hash, net_secret);



	seq = hash[0] | (((u64)hash[1]) << 32);

	seq += ktime_to_ns(ktime_get_real());

	seq &= (1ull << 48) - 1;



	return seq;

}

EXPORT_SYMBOL(secure_dccp_sequence_number);



#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)

u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,

				  __be16 sport, __be16 dport)

{

	u32 secret[MD5_MESSAGE_BYTES / 4];

	u32 hash[MD5_DIGEST_WORDS];

	u64 seq;

	u32 i;



	memcpy(hash, saddr, 16);

	for (i = 0; i < 4; i++)

		secret[i] = net_secret[i] + daddr[i];

	secret[4] = net_secret[4] +

		(((__force u16)sport << 16) + (__force u16)dport);

	for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)

		secret[i] = net_secret[i];



	md5_transform(hash, secret);



	seq = hash[0] | (((u64)hash[1]) << 32);

	seq += ktime_to_ns(ktime_get_real());

	seq &= (1ull << 48) - 1;



	return seq;

}

EXPORT_SYMBOL(secure_dccpv6_sequence_number);

#endif

#endif

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