[PATCH net-next 1/5] tcp: Create list of TFO-contexts

[Christoph Paasch <cpaasch@apple.com>]

Instead of having a single TFO-context, we now have a list of
tcp_fastopen_context, bounded by TCP_FASTOPEN_CTXT_LEN (set to 2).

This enables us to do a rolling TFO-key update that allows the server to
accept old cookies and at the same time announce new ones to the client
(see follow-up patch).

Signed-off-by: Christoph Paasch <cpaasch@apple.com>
---
 include/net/tcp.h       |  2 ++
 net/ipv4/tcp_fastopen.c | 52 +++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index e0a65c067662..e629ea2e6c9d 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1622,9 +1622,11 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
 			     struct tcp_fastopen_cookie *cookie);
 bool tcp_fastopen_defer_connect(struct sock *sk, int *err);
 #define TCP_FASTOPEN_KEY_LENGTH 16
+#define TCP_FASTOPEN_CTXT_LEN 2
 
 /* Fastopen key context */
 struct tcp_fastopen_context {
+	struct tcp_fastopen_context __rcu *next;
 	struct crypto_cipher	*tfm;
 	__u8			key[TCP_FASTOPEN_KEY_LENGTH];
 	struct rcu_head		rcu;
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 018a48477355..c52d5b8eabf0 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -37,8 +37,14 @@ static void tcp_fastopen_ctx_free(struct rcu_head *head)
 {
 	struct tcp_fastopen_context *ctx =
 	    container_of(head, struct tcp_fastopen_context, rcu);
-	crypto_free_cipher(ctx->tfm);
-	kfree(ctx);
+
+	while (ctx) {
+		struct tcp_fastopen_context *prev = ctx;
+		/* We own ctx, thus no need to hold the Fastopen-lock */
+		ctx = rcu_dereference_protected(ctx->next, 1);
+		crypto_free_cipher(prev->tfm);
+		kfree(prev);
+	}
 }
 
 void tcp_fastopen_destroy_cipher(struct sock *sk)
@@ -66,6 +72,35 @@ void tcp_fastopen_ctx_destroy(struct net *net)
 		call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
 }
 
+static struct tcp_fastopen_context *
+tcp_fastopen_cut_keypool(struct tcp_fastopen_context *ctx,
+			 spinlock_t *lock)
+{
+	int cnt = 0;
+
+	while (ctx) {
+		/* We iterate the list to see if we have more than
+		 * TCP_FASTOPEN_CTXT_LEN contexts. If we do, we remove the rest
+		 * of the list and free it later
+		 */
+
+		cnt++;
+		if (cnt >= TCP_FASTOPEN_CTXT_LEN) {
+			/* It's the last one, return the rest so it gets freed */
+			struct tcp_fastopen_context *prev = ctx;
+
+			ctx = rcu_dereference_protected(ctx->next,
+							lockdep_is_held(lock));
+			rcu_assign_pointer(prev->next, NULL);
+			break;
+		}
+		ctx = rcu_dereference_protected(ctx->next,
+						lockdep_is_held(lock));
+	}
+
+	return ctx;
+}
+
 int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
 			      void *key, unsigned int len)
 {
@@ -96,13 +131,22 @@ error:		kfree(ctx);
 	spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
 	if (sk) {
 		q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
+		rcu_assign_pointer(ctx->next, q->ctx);
+		rcu_assign_pointer(q->ctx, ctx);
+
 		octx = rcu_dereference_protected(q->ctx,
 			lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
-		rcu_assign_pointer(q->ctx, ctx);
+
+		octx = tcp_fastopen_cut_keypool(octx, &net->ipv4.tcp_fastopen_ctx_lock);
 	} else {
+		rcu_assign_pointer(ctx->next, net->ipv4.tcp_fastopen_ctx);
+		rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);
+
 		octx = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
 			lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
-		rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);
+
+		octx = tcp_fastopen_cut_keypool(octx,
+						&net->ipv4.tcp_fastopen_ctx_lock);
 	}
 	spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
 
-- 
2.16.2