@@ -58,12 +58,7 @@ static inline unsigned int tcp_optlen(const struct sk_buff *skb)
/* TCP Fast Open Cookie as stored in memory */
struct tcp_fastopen_cookie {
- union {
- u8 val[TCP_FASTOPEN_COOKIE_MAX];
-#if IS_ENABLED(CONFIG_IPV6)
- struct in6_addr addr;
-#endif
- };
+ u64 val[TCP_FASTOPEN_COOKIE_MAX / sizeof(u64)];
s8 len;
bool exp; /* In RFC6994 experimental option format */
};
@@ -1624,7 +1624,6 @@ bool tcp_fastopen_defer_connect(struct sock *sk, int *err);
/* Fastopen key context */
struct tcp_fastopen_context {
- struct crypto_cipher *tfm;
__u8 key[TCP_FASTOPEN_KEY_LENGTH];
struct rcu_head rcu;
};
@@ -7,6 +7,7 @@
#include <linux/tcp.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
+#include <linux/siphash.h>
#include <net/inetpeer.h>
#include <net/tcp.h>
@@ -37,8 +38,7 @@ 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);
+ kzfree(ctx);
}
void tcp_fastopen_destroy_cipher(struct sock *sk)
@@ -76,23 +76,9 @@ int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
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(&net->ipv4.tcp_fastopen_ctx_lock);
if (sk) {
q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
@@ -112,11 +98,14 @@ error: kfree(ctx);
}
static bool __tcp_fastopen_cookie_gen(struct sock *sk, const void *path,
- struct tcp_fastopen_cookie *foc)
+ int size, struct tcp_fastopen_cookie *foc)
{
struct tcp_fastopen_context *ctx;
bool ok = false;
+ BUILD_BUG_ON(sizeof(siphash_key_t) != TCP_FASTOPEN_KEY_LENGTH);
+ BUILD_BUG_ON(sizeof(u64) != TCP_FASTOPEN_COOKIE_SIZE);
+
rcu_read_lock();
ctx = rcu_dereference(inet_csk(sk)->icsk_accept_queue.fastopenq.ctx);
@@ -124,7 +113,7 @@ static bool __tcp_fastopen_cookie_gen(struct sock *sk, const void *path,
ctx = rcu_dereference(sock_net(sk)->ipv4.tcp_fastopen_ctx);
if (ctx) {
- crypto_cipher_encrypt_one(ctx->tfm, foc->val, path);
+ foc->val[0] = siphash(path, size, (siphash_key_t *)&ctx->key);
foc->len = TCP_FASTOPEN_COOKIE_SIZE;
ok = true;
}
@@ -132,11 +121,8 @@ static bool __tcp_fastopen_cookie_gen(struct sock *sk, const void *path,
return ok;
}
-/* Generate the fastopen cookie by doing aes128 encryption on both
- * the source and destination addresses. Pad 0s for IPv4 or IPv4-mapped-IPv6
- * addresses. For the longer IPv6 addresses use CBC-MAC.
- *
- * XXX (TFO) - refactor when TCP_FASTOPEN_COOKIE_SIZE != AES_BLOCK_SIZE.
+/* Generate the fastopen cookie by applying SipHash to both the source and
+ * destination addresses.
*/
static bool tcp_fastopen_cookie_gen(struct sock *sk,
struct request_sock *req,
@@ -146,25 +132,20 @@ static bool tcp_fastopen_cookie_gen(struct sock *sk,
if (req->rsk_ops->family == AF_INET) {
const struct iphdr *iph = ip_hdr(syn);
- __be32 path[4] = { iph->saddr, iph->daddr, 0, 0 };
- return __tcp_fastopen_cookie_gen(sk, path, foc);
+ return __tcp_fastopen_cookie_gen(sk, &iph->saddr,
+ sizeof(iph->saddr) +
+ sizeof(iph->daddr),
+ foc);
}
-#if IS_ENABLED(CONFIG_IPV6)
- if (req->rsk_ops->family == AF_INET6) {
+ if (IS_ENABLED(CONFIG_IPV6) && req->rsk_ops->family == AF_INET6) {
const struct ipv6hdr *ip6h = ipv6_hdr(syn);
- struct tcp_fastopen_cookie tmp;
-
- if (__tcp_fastopen_cookie_gen(sk, &ip6h->saddr, &tmp)) {
- struct in6_addr *buf = &tmp.addr;
- int i;
- for (i = 0; i < 4; i++)
- buf->s6_addr32[i] ^= ip6h->daddr.s6_addr32[i];
- return __tcp_fastopen_cookie_gen(sk, buf, foc);
- }
+ return __tcp_fastopen_cookie_gen(sk, &ip6h->saddr,
+ sizeof(ip6h->saddr) +
+ sizeof(ip6h->daddr),
+ foc);
}
-#endif
return false;
}
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. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- NOTE: This approach assumes that there are no external dependencies, i.e., that there are no tools that implement the same algorithm to calculate TCP fastopen cookies outside of the kernel. include/linux/tcp.h | 7 +-- include/net/tcp.h | 1 - net/ipv4/tcp_fastopen.c | 55 +++++++------------- 3 files changed, 19 insertions(+), 44 deletions(-) -- 2.20.1