net: Update window_clamp if SOCK_RCVBUF is set

When net.ipv4.tcp_syncookies=1 and syn flood is happened,
cookie_v4_check or cookie_v6_check tries to redo what
tcp_v4_send_synack or tcp_v6_send_synack did,
rsk_window_clamp will be changed if SOCK_RCVBUF is set,
which will make rcv_wscale is different, the client
still operates with initial window scale and can overshot
granted window, the client use the initial scale but local
server use new scale to advertise window value, and session
work abnormally.

Fixes: 8c7d7b4403c0 ("tcp: allow effective reduction of TCP's rcv-buffer via setsockopt")
Signed-off-by: Mao Wenan <wenan.mao@linux.alibaba.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/1604967391-123737-1-git-send-email-wenan.mao@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 6ac473b47f30d4d5e5e9455424b1a91d84e649ee..00dc3f943c80b5a1815180e00aeebf532100140e 100644 (file)
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -331,7 +331,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
        __u32 cookie = ntohl(th->ack_seq) - 1;
        struct sock *ret = sk;
        struct request_sock *req;
-       int mss;
+       int full_space, mss;
        struct rtable *rt;
        __u8 rcv_wscale;
        struct flowi4 fl4;
@@ -427,8 +427,13 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 
        /* Try to redo what tcp_v4_send_synack did. */
        req->rsk_window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
+       /* limit the window selection if the user enforce a smaller rx buffer */
+       full_space = tcp_full_space(sk);
+       if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
+           (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
+               req->rsk_window_clamp = full_space;
 
-       tcp_select_initial_window(sk, tcp_full_space(sk), req->mss,
+       tcp_select_initial_window(sk, full_space, req->mss,
                                  &req->rsk_rcv_wnd, &req->rsk_window_clamp,
                                  ireq->wscale_ok, &rcv_wscale,
                                  dst_metric(&rt->dst, RTAX_INITRWND));

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index e796a64be308ccf6d1fc2d6c726d3f1763aafb8b..9b6cae1e49d9102fb0b27a7c3501e65aa3f17402 100644 (file)
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -136,7 +136,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
        __u32 cookie = ntohl(th->ack_seq) - 1;
        struct sock *ret = sk;
        struct request_sock *req;
-       int mss;
+       int full_space, mss;
        struct dst_entry *dst;
        __u8 rcv_wscale;
        u32 tsoff = 0;
@@ -241,7 +241,13 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
        }
 
        req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
-       tcp_select_initial_window(sk, tcp_full_space(sk), req->mss,
+       /* limit the window selection if the user enforce a smaller rx buffer */
+       full_space = tcp_full_space(sk);
+       if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
+           (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))
+               req->rsk_window_clamp = full_space;
+
+       tcp_select_initial_window(sk, full_space, req->mss,
                                  &req->rsk_rcv_wnd, &req->rsk_window_clamp,
                                  ireq->wscale_ok, &rcv_wscale,
                                  dst_metric(dst, RTAX_INITRWND));