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Commit 222e83d2 authored by Hannes Frederic Sowa's avatar Hannes Frederic Sowa Committed by David S. Miller
Browse files

tcp: switch tcp_fastopen key generation to net_get_random_once 



Changed key initialization of tcp_fastopen cookies to net_get_random_once.

If the user sets a custom key net_get_random_once must be called at
least once to ensure we don't overwrite the user provided key when the
first cookie is generated later on.

Cc: Yuchung Cheng <ycheng@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1bbdceef

include/net/tcp.h

+1 −1
Original line number Diff line number Diff line
@@ -1322,7 +1322,7 @@ extern struct tcp_fastopen_context __rcu *tcp_fastopen_ctx; 
int tcp_fastopen_reset_cipher(void *key, unsigned int len);

void tcp_fastopen_cookie_gen(__be32 src, __be32 dst,

			     struct tcp_fastopen_cookie *foc);



void tcp_fastopen_init_key_once(bool publish);

#define TCP_FASTOPEN_KEY_LENGTH 16



/* Fastopen key context */

net/ipv4/sysctl_net_ipv4.c

+5 −0
Original line number Diff line number Diff line
@@ -274,6 +274,11 @@ static int proc_tcp_fastopen_key(struct ctl_table *ctl, int write, 
			ret = -EINVAL;

			goto bad_key;

		}

		/* Generate a dummy secret but don't publish it. This

		 * is needed so we don't regenerate a new key on the

		 * first invocation of tcp_fastopen_cookie_gen

		 */

		tcp_fastopen_init_key_once(false);

		tcp_fastopen_reset_cipher(user_key, TCP_FASTOPEN_KEY_LENGTH);

	}

net/ipv4/tcp_fastopen.c

+16 −11
Original line number Diff line number Diff line
@@ -14,6 +14,20 @@ struct tcp_fastopen_context __rcu *tcp_fastopen_ctx; 


static DEFINE_SPINLOCK(tcp_fastopen_ctx_lock);



void tcp_fastopen_init_key_once(bool publish)

{

	static u8 key[TCP_FASTOPEN_KEY_LENGTH];



	/* tcp_fastopen_reset_cipher publishes the new context

	 * atomically, so we allow this race happening here.

	 *

	 * All call sites of tcp_fastopen_cookie_gen also check

	 * for a valid cookie, so this is an acceptable risk.

	 */

	if (net_get_random_once(key, sizeof(key)) && publish)

		tcp_fastopen_reset_cipher(key, sizeof(key));

}



static void tcp_fastopen_ctx_free(struct rcu_head *head)

{

	struct tcp_fastopen_context *ctx =
@@ -70,6 +84,8 @@ void tcp_fastopen_cookie_gen(__be32 src, __be32 dst, 
	__be32 path[4] = { src, dst, 0, 0 };

	struct tcp_fastopen_context *ctx;



	tcp_fastopen_init_key_once(true);



	rcu_read_lock();

	ctx = rcu_dereference(tcp_fastopen_ctx);

	if (ctx) {
@@ -78,14 +94,3 @@ void tcp_fastopen_cookie_gen(__be32 src, __be32 dst, 
	}

	rcu_read_unlock();

}
 


static int __init tcp_fastopen_init(void)

{

	__u8 key[TCP_FASTOPEN_KEY_LENGTH];



	get_random_bytes(key, sizeof(key));

	tcp_fastopen_reset_cipher(key, sizeof(key));

	return 0;

}



late_initcall(tcp_fastopen_init);