Merge branch 'listener-sock-const'

Eric Dumazet says:

====================
dccp/tcp: constify listener sock

Another patch bomb to prepare lockless TCP/DCCP LISTEN handling.

SYNACK retransmits are built and sent without listener socket
being locked. Soon, initial SYNACK packets will have same property.

This series makes sure we did not something wrong with this model,
by adding a const qualifier in all the paths taken from synack building
and transmit, for IPv4/IPv6 and TCP/dccp.

The only potential problem was the rewrite of ecn bits for connections
with DCTCP as congestion module, but this was a very minor one.
====================

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

1 files changed, 18 insertions, 10 deletions

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 85830bb92d04..e0a87c238882 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -362,27 +362,35 @@ void tcp_twsk_destructor(struct sock *sk)
 }
 EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
 
+/* Warning : This function is called without sk_listener being locked.
+ * Be sure to read socket fields once, as their value could change under us.
+ */
 void tcp_openreq_init_rwin(struct request_sock *req,
-                           struct sock *sk, struct dst_entry *dst)
+                           const struct sock *sk_listener,
+                           const struct dst_entry *dst)
 {
         struct inet_request_sock *ireq = inet_rsk(req);
-        struct tcp_sock *tp = tcp_sk(sk);
-        __u8 rcv_wscale;
+        const struct tcp_sock *tp = tcp_sk(sk_listener);
+        u16 user_mss = READ_ONCE(tp->rx_opt.user_mss);
+        int full_space = tcp_full_space(sk_listener);
         int mss = dst_metric_advmss(dst);
+        u32 window_clamp;
+        __u8 rcv_wscale;
 
-        if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
-                mss = tp->rx_opt.user_mss;
+        if (user_mss && user_mss < mss)
+                mss = user_mss;
 
+        window_clamp = READ_ONCE(tp->window_clamp);
         /* Set this up on the first call only */
-        req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
+        req->window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
 
         /* limit the window selection if the user enforce a smaller rx buffer */
-        if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
-            (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
-                req->window_clamp = tcp_full_space(sk);
+        if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK &&
+            (req->window_clamp > full_space || req->window_clamp == 0))
+                req->window_clamp = full_space;
 
         /* tcp_full_space because it is guaranteed to be the first packet */
-        tcp_select_initial_window(tcp_full_space(sk),
+        tcp_select_initial_window(full_space,
                 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
                 &req->rcv_wnd,
                 &req->window_clamp,