tcp_fastopen.c
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#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/tcp.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <net/inetpeer.h>
#include <net/tcp.h>
int sysctl_tcp_fastopen __read_mostly = TFO_CLIENT_ENABLE;
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 =
container_of(head, struct tcp_fastopen_context, rcu);
crypto_free_cipher(ctx->tfm);
kfree(ctx);
}
int tcp_fastopen_reset_cipher(void *key, unsigned int len)
{
int err;
struct tcp_fastopen_context *ctx, *octx;
ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
return -ENOMEM;
ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
if (IS_ERR(ctx->tfm)) {
err = PTR_ERR(ctx->tfm);
error: kfree(ctx);
pr_err("TCP: TFO aes cipher alloc error: %d\n", err);
return err;
}
err = crypto_cipher_setkey(ctx->tfm, key, len);
if (err) {
pr_err("TCP: TFO cipher key error: %d\n", err);
crypto_free_cipher(ctx->tfm);
goto error;
}
memcpy(ctx->key, key, len);
spin_lock(&tcp_fastopen_ctx_lock);
octx = rcu_dereference_protected(tcp_fastopen_ctx,
lockdep_is_held(&tcp_fastopen_ctx_lock));
rcu_assign_pointer(tcp_fastopen_ctx, ctx);
spin_unlock(&tcp_fastopen_ctx_lock);
if (octx)
call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
return err;
}
/* Computes the fastopen cookie for the IP path.
* The path is a 128 bits long (pad with zeros for IPv4).
*
* The caller must check foc->len to determine if a valid cookie
* has been generated successfully.
*/
void tcp_fastopen_cookie_gen(__be32 src, __be32 dst,
struct tcp_fastopen_cookie *foc)
{
__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) {
crypto_cipher_encrypt_one(ctx->tfm, foc->val, (__u8 *)path);
foc->len = TCP_FASTOPEN_COOKIE_SIZE;
}
rcu_read_unlock();
}