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@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 74d3ed5..fd40f8c 100644 (file)
--- 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 983f04c..7ea7034 100644 (file)
--- 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 f4f2a0a..d2a5763 100644 (file)
--- 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 7d2dc01..6451b83 100644 (file)
--- 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 0e621bc..800265c 100644 (file)
--- 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,