From 36d7b99b7a7de6b3c4dd6c206fb52135f51ac609 Mon Sep 17 00:00:00 2001 From: Mao Wenan Date: Tue, 10 Nov 2020 08:16:31 +0800 Subject: 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 Signed-off-by: Eric Dumazet Link: https://lore.kernel.org/r/1604967391-123737-1-git-send-email-wenan.mao@linux.alibaba.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/ipv4/syncookies.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'net/ipv4') diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index f3d3ac5c23d5..d9e7d61a0197 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -307,7 +307,7 @@ 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; @@ -391,8 +391,13 @@ 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)); -- cgit v1.2.3