tcp: constify tcp_openreq_init_rwin()

Soon, listener socket wont be locked when tcp_openreq_init_rwin()
is called. We need to read socket fields once, as their value
could change under us.

Signed-off-by: Eric Dumazet <edumazet@google.com>
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,