netdev - [PATCH net-next] tcp: tcp_fragment() should not assume rtx skbs

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Date:   Thu, 02 Nov 2017 18:10:03 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>, Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Priyaranjan Jha <priyarjha@...gle.com>
Subject: [PATCH net-next] tcp: tcp_fragment() should not assume rtx skbs

From: Eric Dumazet <edumazet@...gle.com>

While stress testing MTU probing, we had crashes in list_del() that we root-caused
to the fact that tcp_fragment() is unconditionally inserting the freshly allocated
skb into tsorted_sent_queue list.

But this list is supposed to contain skbs that were sent.
This was mostly harmless until MTU probing was enabled.

Fortunately we can use the tcp_queue enum added later (but in same linux version)
for rtx-rb-tree to fix the bug. 

Fixes: e2080072ed2d ("tcp: new list for sent but unacked skbs for RACK recovery")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Yuchung Cheng <ycheng@...gle.com>
Cc: Neal Cardwell <ncardwell@...gle.com>
Cc: Soheil Hassas Yeganeh <soheil@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Priyaranjan Jha <priyarjha@...gle.com>
---
 net/ipv4/tcp_output.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a85e8a282d173983e35a2a1e3135ca2a63f1699e..36a3e7c909caacd981b84d1d8820a33d922f5a4e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1395,7 +1395,8 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
 	/* Link BUFF into the send queue. */
 	__skb_header_release(buff);
 	tcp_insert_write_queue_after(skb, buff, sk, tcp_queue);
-	list_add(&buff->tcp_tsorted_anchor, &skb->tcp_tsorted_anchor);
+	if (tcp_queue == TCP_FRAG_IN_RTX_QUEUE)
+		list_add(&buff->tcp_tsorted_anchor, &skb->tcp_tsorted_anchor);
 
 	return 0;
 }