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net: Compute protocol sequence numbers and fragment IDs using MD5.
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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]>
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davem330 committed Aug 7, 2011
1 parent bc0b96b commit 6e5714e
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349 changes: 8 additions & 341 deletions drivers/char/random.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1300,363 +1300,30 @@ 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 <[email protected]>
*
*/
#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 <[email protected]>.
*/
__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
* with the goal of minimal entropy pool depletion. As a result, the random
* 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;
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12 changes: 0 additions & 12 deletions include/linux/random.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
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