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tcp: miscounts due to tcp_fragment pcount reset

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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>
This commit is contained in:
Ilpo Järvinen 2009-04-01 23:18:20 +00:00 committed by David S. Miller
parent 797108d134
commit 9eb9362e56
1 changed files with 6 additions and 1 deletions
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7
net/ipv4/tcp_output.c
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@ -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 {
tcp_init_tso_segs(sk, skb, cur_mss);
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);