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Date: Wed, 13 Apr 2016 22:05:39 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next 1/2] tcp: do not mess with listener sk_wmem_alloc
When removing sk_refcnt manipulation on synflood, I missed that
using skb_set_owner_w() was racy, if sk->sk_wmem_alloc had already
transitioned to 0.
We should hold sk_refcnt instead, but this is a big deal under attack.
(Doing so increase performance from 3.2 Mpps to 3.8 Mpps only)
In this patch, I chose to not attach a socket to syncookies skb.
Performance is now 5 Mpps instead of 3.2 Mpps.
Following patch will remove last known false sharing in
tcp_rcv_state_process()
Fixes: 3b24d854cb35 ("tcp/dccp: do not touch listener sk_refcnt under synflood")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
include/net/tcp.h | 9 +++++++--
net/ipv4/tcp_input.c | 7 ++++---
net/ipv4/tcp_ipv4.c | 4 ++--
net/ipv4/tcp_output.c | 16 ++++++++++++----
net/ipv6/tcp_ipv6.c | 4 ++--
5 files changed, 27 insertions(+), 13 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 74d3ed5eb219..fd40f8c64d5f 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -452,10 +452,15 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
int tcp_connect(struct sock *sk);
+enum tcp_synack_type {
+ TCP_SYNACK_NORMAL,
+ TCP_SYNACK_FASTOPEN,
+ TCP_SYNACK_COOKIE,
+};
struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
struct request_sock *req,
struct tcp_fastopen_cookie *foc,
- bool attach_req);
+ enum tcp_synack_type synack_type);
int tcp_disconnect(struct sock *sk, int flags);
void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
@@ -1728,7 +1733,7 @@ struct tcp_request_sock_ops {
int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
struct flowi *fl, struct request_sock *req,
struct tcp_fastopen_cookie *foc,
- bool attach_req);
+ enum tcp_synack_type synack_type);
};
#ifdef CONFIG_SYN_COOKIES
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 983f04c11177..7ea7034af83f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6327,7 +6327,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
}
if (fastopen_sk) {
af_ops->send_synack(fastopen_sk, dst, &fl, req,
- &foc, false);
+ &foc, TCP_SYNACK_FASTOPEN);
/* Add the child socket directly into the accept queue */
inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
sk->sk_data_ready(sk);
@@ -6337,8 +6337,9 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
tcp_rsk(req)->tfo_listener = false;
if (!want_cookie)
inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
- af_ops->send_synack(sk, dst, &fl, req,
- &foc, !want_cookie);
+ af_ops->send_synack(sk, dst, &fl, req, &foc,
+ !want_cookie ? TCP_SYNACK_NORMAL :
+ TCP_SYNACK_COOKIE);
if (want_cookie) {
reqsk_free(req);
return 0;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index f4f2a0a3849d..d2a5763e5abc 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -830,7 +830,7 @@ static int tcp_v4_send_synack(const struct sock *sk, struct dst_entry *dst,
struct flowi *fl,
struct request_sock *req,
struct tcp_fastopen_cookie *foc,
- bool attach_req)
+ enum tcp_synack_type synack_type)
{
const struct inet_request_sock *ireq = inet_rsk(req);
struct flowi4 fl4;
@@ -841,7 +841,7 @@ static int tcp_v4_send_synack(const struct sock *sk, struct dst_entry *dst,
if (!dst && (dst = inet_csk_route_req(sk, &fl4, req)) == NULL)
return -1;
- skb = tcp_make_synack(sk, dst, req, foc, attach_req);
+ skb = tcp_make_synack(sk, dst, req, foc, synack_type);
if (skb) {
__tcp_v4_send_check(skb, ireq->ir_loc_addr, ireq->ir_rmt_addr);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7d2dc015cd19..6451b83d81e9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2944,7 +2944,7 @@ int tcp_send_synack(struct sock *sk)
struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
struct request_sock *req,
struct tcp_fastopen_cookie *foc,
- bool attach_req)
+ enum tcp_synack_type synack_type)
{
struct inet_request_sock *ireq = inet_rsk(req);
const struct tcp_sock *tp = tcp_sk(sk);
@@ -2964,14 +2964,22 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
/* Reserve space for headers. */
skb_reserve(skb, MAX_TCP_HEADER);
- if (attach_req) {
+ switch (synack_type) {
+ case TCP_SYNACK_NORMAL:
skb_set_owner_w(skb, req_to_sk(req));
- } else {
+ break;
+ case TCP_SYNACK_COOKIE:
+ /* Under synflood, we do not attach skb to a socket,
+ * to avoid false sharing.
+ */
+ break;
+ case TCP_SYNACK_FASTOPEN:
/* sk is a const pointer, because we want to express multiple
* cpu might call us concurrently.
* sk->sk_wmem_alloc in an atomic, we can promote to rw.
*/
skb_set_owner_w(skb, (struct sock *)sk);
+ break;
}
skb_dst_set(skb, dst);
@@ -3516,7 +3524,7 @@ int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
int res;
tcp_rsk(req)->txhash = net_tx_rndhash();
- res = af_ops->send_synack(sk, NULL, &fl, req, NULL, true);
+ res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
if (!res) {
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 0e621bc1ae11..800265c7fd3f 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -439,7 +439,7 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
struct flowi *fl,
struct request_sock *req,
struct tcp_fastopen_cookie *foc,
- bool attach_req)
+ enum tcp_synack_type synack_type)
{
struct inet_request_sock *ireq = inet_rsk(req);
struct ipv6_pinfo *np = inet6_sk(sk);
@@ -452,7 +452,7 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
IPPROTO_TCP)) == NULL)
goto done;
- skb = tcp_make_synack(sk, dst, req, foc, attach_req);
+ skb = tcp_make_synack(sk, dst, req, foc, synack_type);
if (skb) {
__tcp_v6_send_check(skb, &ireq->ir_v6_loc_addr,
--
2.8.0.rc3.226.g39d4020
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