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 b596c413d297c44e849dedd034fbe1fc610b9cb0..bcf743432c8def94b000983ef1d6e4a948c45226 100644 (file)
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -304,7 +304,7 @@ 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;
@@ -388,8 +388,13 @@ 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 4834015b27f49ceef981cd2dd2a3ebd3564d0813..0e368c1dd78b805d9e9bf70ab67c210f7481809e 100644 (file)
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -143,7 +143,7 @@ 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;
 
@@ -236,7 +236,13 @@ 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));