Commit 9eb9362e authored Apr 01, 2009 by Ilpo Järvinen Committed by David S. Miller Apr 02, 2009

tcp: miscounts due to tcp_fragment pcount reset



It seems that trivial reset of pcount to one was not sufficient
in tcp_retransmit_skb. Multiple counters experience a positive
miscount when skb's pcount gets lowered without the necessary
adjustments (depending on skb's sacked bits which exactly), at
worst a packets_out miscount can crash at RTO if the write queue
is empty!

Triggering this requires mss change, so bidir tcp or mtu probe or
like.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Tested-by: Uwe Bugla <uwe.bugla@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 797108d1

net/ipv4/tcp_output.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -1893,7 +1893,12 @@ int tcp_retransmit_skb(struct sock sk, struct sk_buff skb)
		if (tcp_fragment(sk, skb, cur_mss, cur_mss))
		return -ENOMEM; /* We'll try again later. */
		} else {
		int oldpcount = tcp_skb_pcount(skb);

		if (unlikely(oldpcount > 1)) {
		tcp_init_tso_segs(sk, skb, cur_mss);
		tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
		}
		}

		tcp_retrans_try_collapse(sk, skb, cur_mss);

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