netdev - Re: [PATCH] tcp: Avoid infinite loop on recvmsg bug

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Date:	Wed, 07 Nov 2012 15:42:34 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Julius Werner <jwerner@...omium.org>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Patrick McHardy <kaber@...sh.net>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	James Morris <jmorris@...ei.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Dave Jones <davej@...hat.com>,
	Sameer Nanda <snanda@...omium.org>,
	Mandeep Singh Baines <msb@...omium.org>
Subject: Re: [PATCH] tcp: Avoid infinite loop on recvmsg bug

On Wed, 2012-11-07 at 15:33 -0800, Eric Dumazet wrote:

> So you probably are fighting a bug we already fixed in upstream kernel.
> 
> (commit c8628155ece363 "tcp: reduce out_of_order memory use" did not
> played well with cloned skbs.)
> 
> This issue was already discussed on netdev in the past.

If you use a 3.4 kernel, you want the following patch.

(I guess you could reproduce the crash easily running a tcpdump in //)


diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 257b617..9f8f68c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4496,7 +4496,9 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
 		 * to avoid future tcp_collapse_ofo_queue(),
 		 * probably the most expensive function in tcp stack.
 		 */
-		if (skb->len <= skb_tailroom(skb1) && !tcp_hdr(skb)->fin) {
+		if (skb->len <= skb_tailroom(skb1) &&
+		    !tcp_hdr(skb)->fin &&
+		    !skb_cloned(skb1)) {
 			NET_INC_STATS_BH(sock_net(sk),
 					 LINUX_MIB_TCPRCVCOALESCE);
 			BUG_ON(skb_copy_bits(skb, 0,



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