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Date:	Wed, 07 Nov 2012 15:42:34 -0800
From:	Eric Dumazet <>
To:	Julius Werner <>
	Patrick McHardy <>,
	Hideaki YOSHIFUJI <>,
	James Morris <>,
	Alexey Kuznetsov <>,
	"David S. Miller" <>,
	Dave Jones <>,
	Sameer Nanda <>,
	Mandeep Singh Baines <>
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)) {
 			BUG_ON(skb_copy_bits(skb, 0,

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