path: root/include/net/tcp.h
diff options
authorArd Biesheuvel <ard.biesheuvel@linaro.org>2019-06-17 10:09:33 +0200
committerDavid S. Miller <davem@davemloft.net>2019-06-17 13:56:26 -0700
commitc681edae33e86ff27be2d6cc717663d91df20b0e (patch)
tree95e0fb78d34c4a223c29fb265ea0033be8c78db7 /include/net/tcp.h
parenttipc: include retrans failure detection for unicast (diff)
net: ipv4: move tcp_fastopen server side code to SipHash library
Using a bare block cipher in non-crypto code is almost always a bad idea, not only for security reasons (and we've seen some examples of this in the kernel in the past), but also for performance reasons. In the TCP fastopen case, we call into the bare AES block cipher one or two times (depending on whether the connection is IPv4 or IPv6). On most systems, this results in a call chain such as crypto_cipher_encrypt_one(ctx, dst, src) crypto_cipher_crt(tfm)->cit_encrypt_one(crypto_cipher_tfm(tfm), ...); aesni_encrypt kernel_fpu_begin(); aesni_enc(ctx, dst, src); // asm routine kernel_fpu_end(); It is highly unlikely that the use of special AES instructions has a benefit in this case, especially since we are doing the above twice for IPv6 connections, instead of using a transform which can process the entire input in one go. We could switch to the cbcmac(aes) shash, which would at least get rid of the duplicated overhead in *some* cases (i.e., today, only arm64 has an accelerated implementation of cbcmac(aes), while x86 will end up using the generic cbcmac template wrapping the AES-NI cipher, which basically ends up doing exactly the above). However, in the given context, it makes more sense to use a light-weight MAC algorithm that is more suitable for the purpose at hand, such as SipHash. Since the output size of SipHash already matches our chosen value for TCP_FASTOPEN_COOKIE_SIZE, and given that it accepts arbitrary input sizes, this greatly simplifies the code as well. NOTE: Server farms backing a single server IP for load balancing purposes and sharing a single fastopen key will be adversely affected by this change unless all systems in the pool receive their kernel upgrades at the same time. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/tcp.h')
1 files changed, 4 insertions, 6 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 96e0e53ff440..184930b02779 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1628,9 +1628,9 @@ bool tcp_fastopen_defer_connect(struct sock *sk, int *err);
/* Fastopen key context */
struct tcp_fastopen_context {
- struct crypto_cipher *tfm[TCP_FASTOPEN_KEY_MAX];
- struct rcu_head rcu;
+ int num;
+ struct rcu_head rcu;
extern unsigned int sysctl_tcp_fastopen_blackhole_timeout;
@@ -1665,9 +1665,7 @@ bool tcp_fastopen_cookie_match(const struct tcp_fastopen_cookie *foc,
static inline
int tcp_fastopen_context_len(const struct tcp_fastopen_context *ctx)
- if (ctx->tfm[1])
- return 2;
- return 1;
+ return ctx->num;
/* Latencies incurred by various limits for a sender. They are