@@ -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);
@@ -1474,6 +1474,14 @@ 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);
@@ -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>
@@ -2842,6 +2843,141 @@ 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 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 */
+ spin_unlock_bh(&tcp_secret_locker);
+ memcpy(bakery,
+ &tcp_secret_generating->secrets[0],
+ sizeof(tcp_secret_generating->secrets));
+ } else {
+ u32 secrets[COOKIE_WORKSPACE_WORDS];
+
+ /* still needs refreshing */
+ get_random_bytes(secrets, sizeof(secrets));
+
+ /* 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);
+ secrets[COOKIE_DIGEST_WORDS+0] ^=
+ (u32)tv.tv_nsec;
+
+ tcp_secret_secondary->expires = jiffy
+ + TCP_SECRET_1MSL
+ + (0x0f & tcp_cookie_work(secrets, 0));
+ } else {
+ tcp_secret_secondary->expires = jiffy
+ + TCP_SECRET_LIFE
+ + (0xff & tcp_cookie_work(secrets, 1));
+ tcp_secret_primary->expires = jiffy
+ + TCP_SECRET_2MSL
+ + (0x1f & tcp_cookie_work(secrets, 2));
+ }
+ memcpy(&tcp_secret_secondary->secrets[0],
+ &secrets[0],
+ sizeof(secrets));
+
+ rcu_assign_pointer(tcp_secret_generating,
+ tcp_secret_secondary);
+ rcu_assign_pointer(tcp_secret_retiring,
+ tcp_secret_primary);
+ spin_unlock_bh(&tcp_secret_locker);
+ /* Neither call_rcu() or synchronize_rcu() are needed.
+ * Retiring data is not freed. It is replaced after
+ * further (locked) pointer updates, and a quiet time
+ * (minimum 1MSL, maximum LIFE - 2MSL).
+ */
+ memcpy(bakery,
+ &secrets[0],
+ sizeof(secrets));
+ }
+ } else {
+ rcu_read_lock_bh();
+ memcpy(bakery,
+ &rcu_dereference(tcp_secret_generating)->secrets[0],
+ sizeof(tcp_secret_generating->secrets));
+ 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)
@@ -2876,6 +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));
@@ -2969,6 +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);
Define (missing) hash message size for SHA1. Define hashing size constants specific to TCP cookies, and add new function. 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: William.Allen.Simpson@gmail.com --- include/linux/cryptohash.h | 1 + include/net/tcp.h | 8 +++ net/ipv4/tcp.c | 146 ++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 155 insertions(+), 0 deletions(-)