From 25c28af9ee6a9cfeeb9245e174b3b65d70e614b2 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 23 Jul 2018 09:28:18 -0700 Subject: tcp: avoid collapses in tcp_prune_queue() if possible [ Upstream commit f4a3313d8e2ca9fd8d8f45e40a2903ba782607e7 ] Right after a TCP flow is created, receiving tiny out of order packets allways hit the condition : if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) tcp_clamp_window(sk); tcp_clamp_window() increases sk_rcvbuf to match sk_rmem_alloc (guarded by tcp_rmem[2]) Calling tcp_collapse_ofo_queue() in this case is not useful, and offers a O(N^2) surface attack to malicious peers. Better not attempt anything before full queue capacity is reached, forcing attacker to spend lots of resource and allow us to more easily detect the abuse. Signed-off-by: Eric Dumazet Acked-by: Soheil Hassas Yeganeh Acked-by: Yuchung Cheng Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_input.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'net/ipv4') diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 3466d5716d1c..7dd31aec8b48 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4738,6 +4738,9 @@ static int tcp_prune_queue(struct sock *sk) else if (sk_under_memory_pressure(sk)) tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss); + if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) + return 0; + tcp_collapse_ofo_queue(sk); if (!skb_queue_empty(&sk->sk_receive_queue)) tcp_collapse(sk, &sk->sk_receive_queue, -- cgit v1.2.3