Commit da5c78c8 authored by William Allen Simpson's avatar William Allen Simpson Committed by David S. Miller
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TCPCT part 1b: generate Responder Cookie secret 



Define (missing) hash message size for SHA1.

Define hashing size constants specific to TCP cookies.

Add new function: tcp_cookie_generator().

Maintain global secret values for tcp_cookie_generator().

This is a significantly revised implementation of earlier (15-year-old)
Photuris [RFC-2522] code for the KA9Q cooperative multitasking platform.

Linux RCU technique appears to be well-suited to this application, though
neither of the circular queue items are freed.

These functions will also be used in subsequent patches that implement
additional features.

Signed-off-by: default avatar <William.Allen.Simpson@gmail.com>
Acked-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e6b4d113

include/linux/cryptohash.h

+1 −0
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
#define __CRYPTOHASH_H



#define SHA_DIGEST_WORDS 5

#define SHA_MESSAGE_BYTES (512 /*bits*/ / 8)

#define SHA_WORKSPACE_WORDS 80



void sha_init(__u32 *buf);

include/net/tcp.h

+8 −0
Original line number Diff line number Diff line
@@ -1478,6 +1478,14 @@ struct tcp_request_sock_ops { 
#endif

};



/* Using SHA1 for now, define some constants.

 */

#define COOKIE_DIGEST_WORDS (SHA_DIGEST_WORDS)

#define COOKIE_MESSAGE_WORDS (SHA_MESSAGE_BYTES / 4)

#define COOKIE_WORKSPACE_WORDS (COOKIE_DIGEST_WORDS + COOKIE_MESSAGE_WORDS)



extern int tcp_cookie_generator(u32 *bakery);



extern void tcp_v4_init(void);

extern void tcp_init(void);

net/ipv4/tcp.c

+140 −0
Original line number Diff line number Diff line
@@ -264,6 +264,7 @@ 
#include <linux/cache.h>

#include <linux/err.h>

#include <linux/crypto.h>

#include <linux/time.h>



#include <net/icmp.h>

#include <net/tcp.h>
@@ -2848,6 +2849,135 @@ EXPORT_SYMBOL(tcp_md5_hash_key); 


#endif



/**

 * Each Responder maintains up to two secret values concurrently for

 * efficient secret rollover.  Each secret value has 4 states:

 *

 * Generating.  (tcp_secret_generating != tcp_secret_primary)

 *    Generates new Responder-Cookies, but not yet used for primary

 *    verification.  This is a short-term state, typically lasting only

 *    one round trip time (RTT).

 *

 * Primary.  (tcp_secret_generating == tcp_secret_primary)

 *    Used both for generation and primary verification.

 *

 * Retiring.  (tcp_secret_retiring != tcp_secret_secondary)

 *    Used for verification, until the first failure that can be

 *    verified by the newer Generating secret.  At that time, this

 *    cookie's state is changed to Secondary, and the Generating

 *    cookie's state is changed to Primary.  This is a short-term state,

 *    typically lasting only one round trip time (RTT).

 *

 * Secondary.  (tcp_secret_retiring == tcp_secret_secondary)

 *    Used for secondary verification, after primary verification

 *    failures.  This state lasts no more than twice the Maximum Segment

 *    Lifetime (2MSL).  Then, the secret is discarded.

 */

struct tcp_cookie_secret {

	/* The secret is divided into two parts.  The digest part is the

	 * equivalent of previously hashing a secret and saving the state,

	 * and serves as an initialization vector (IV).  The message part

	 * serves as the trailing secret.

	 */

	u32				secrets[COOKIE_WORKSPACE_WORDS];

	unsigned long			expires;

};



#define TCP_SECRET_1MSL (HZ * TCP_PAWS_MSL)

#define TCP_SECRET_2MSL (HZ * TCP_PAWS_MSL * 2)

#define TCP_SECRET_LIFE (HZ * 600)



static struct tcp_cookie_secret tcp_secret_one;

static struct tcp_cookie_secret tcp_secret_two;



/* Essentially a circular list, without dynamic allocation. */

static struct tcp_cookie_secret *tcp_secret_generating;

static struct tcp_cookie_secret *tcp_secret_primary;

static struct tcp_cookie_secret *tcp_secret_retiring;

static struct tcp_cookie_secret *tcp_secret_secondary;



static DEFINE_SPINLOCK(tcp_secret_locker);



/* Select a pseudo-random word in the cookie workspace.

 */

static inline u32 tcp_cookie_work(const u32 *ws, const int n)

{

	return ws[COOKIE_DIGEST_WORDS + ((COOKIE_MESSAGE_WORDS-1) & ws[n])];

}



/* Fill bakery[COOKIE_WORKSPACE_WORDS] with generator, updating as needed.

 * Called in softirq context.

 * Returns: 0 for success.

 */

int tcp_cookie_generator(u32 *bakery)

{

	unsigned long jiffy = jiffies;



	if (unlikely(time_after_eq(jiffy, tcp_secret_generating->expires))) {

		spin_lock_bh(&tcp_secret_locker);

		if (!time_after_eq(jiffy, tcp_secret_generating->expires)) {

			/* refreshed by another */

			memcpy(bakery,

			       &tcp_secret_generating->secrets[0],

			       COOKIE_WORKSPACE_WORDS);

		} else {

			/* still needs refreshing */

			get_random_bytes(bakery, COOKIE_WORKSPACE_WORDS);



			/* The first time, paranoia assumes that the

			 * randomization function isn't as strong.  But,

			 * this secret initialization is delayed until

			 * the last possible moment (packet arrival).

			 * Although that time is observable, it is

			 * unpredictably variable.  Mash in the most

			 * volatile clock bits available, and expire the

			 * secret extra quickly.

			 */

			if (unlikely(tcp_secret_primary->expires ==

				     tcp_secret_secondary->expires)) {

				struct timespec tv;



				getnstimeofday(&tv);

				bakery[COOKIE_DIGEST_WORDS+0] ^=

					(u32)tv.tv_nsec;



				tcp_secret_secondary->expires = jiffy

					+ TCP_SECRET_1MSL

					+ (0x0f & tcp_cookie_work(bakery, 0));

			} else {

				tcp_secret_secondary->expires = jiffy

					+ TCP_SECRET_LIFE

					+ (0xff & tcp_cookie_work(bakery, 1));

				tcp_secret_primary->expires = jiffy

					+ TCP_SECRET_2MSL

					+ (0x1f & tcp_cookie_work(bakery, 2));

			}

			memcpy(&tcp_secret_secondary->secrets[0],

			       bakery, COOKIE_WORKSPACE_WORDS);



			rcu_assign_pointer(tcp_secret_generating,

					   tcp_secret_secondary);

			rcu_assign_pointer(tcp_secret_retiring,

					   tcp_secret_primary);

			/*

			 * Neither call_rcu() nor synchronize_rcu() needed.

			 * Retiring data is not freed.  It is replaced after

			 * further (locked) pointer updates, and a quiet time

			 * (minimum 1MSL, maximum LIFE - 2MSL).

			 */

		}

		spin_unlock_bh(&tcp_secret_locker);

	} else {

		rcu_read_lock_bh();

		memcpy(bakery,

		       &rcu_dereference(tcp_secret_generating)->secrets[0],

		       COOKIE_WORKSPACE_WORDS);

		rcu_read_unlock_bh();

	}

	return 0;

}

EXPORT_SYMBOL(tcp_cookie_generator);



void tcp_done(struct sock *sk)

{

	if (sk->sk_state == TCP_SYN_SENT || sk->sk_state == TCP_SYN_RECV)
@@ -2882,6 +3012,7 @@ void __init tcp_init(void) 
	struct sk_buff *skb = NULL;

	unsigned long nr_pages, limit;

	int order, i, max_share;

	unsigned long jiffy = jiffies;



	BUILD_BUG_ON(sizeof(struct tcp_skb_cb) > sizeof(skb->cb));
@@ -2975,6 +3106,15 @@ void __init tcp_init(void) 
	       tcp_hashinfo.ehash_mask + 1, tcp_hashinfo.bhash_size);



	tcp_register_congestion_control(&tcp_reno);



	memset(&tcp_secret_one.secrets[0], 0, sizeof(tcp_secret_one.secrets));

	memset(&tcp_secret_two.secrets[0], 0, sizeof(tcp_secret_two.secrets));

	tcp_secret_one.expires = jiffy; /* past due */

	tcp_secret_two.expires = jiffy; /* past due */

	tcp_secret_generating = &tcp_secret_one;

	tcp_secret_primary = &tcp_secret_one;

	tcp_secret_retiring = &tcp_secret_two;

	tcp_secret_secondary = &tcp_secret_two;

}



EXPORT_SYMBOL(tcp_close);

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