net: Update window_clamp if SOCK_RCVBUF is set

[ Upstream commit 909172a149749242990a6e64cb55d55460d4e417 ]

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: e88c64f0a425 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 2f871424925eff13a9a42499cbdcf12e45726aa2..bf8df824bae31f1e5b19d0b705705992fa84296e 100644 (file)
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -296,7 +296,7 @@ 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;
@@ -389,8 +389,13 @@ 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(tcp_full_space(sk), req->mss,
+       tcp_select_initial_window(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 0fe8ffcda1d7d50f2a0cb9036932a09ad0df7160..d1bfdb9c2f2da6139c3a916ad4955a9106d575a6 100644 (file)
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -141,7 +141,7 @@ 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;
@@ -244,7 +244,13 @@ 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(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(full_space, req->mss,
                                  &req->rsk_rcv_wnd, &req->rsk_window_clamp,
                                  ireq->wscale_ok, &rcv_wscale,
                                  dst_metric(dst, RTAX_INITRWND));