[TCP]: Update comment of SACK block validator
Just came across what RFC2018 states about generation of valid SACK blocks in case of reneging. Alter comment a bit to point out clearly. IMHO, there isn't any reason to change code because the validation is there for a purpose (counters will inform user about decision TCP made if this case ever surfaces). Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -1027,8 +1027,15 @@ static void tcp_update_reordering(struct sock *sk, const int metric,
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* SACK block range validation checks that the received SACK block fits to
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* the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
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* Note that SND.UNA is not included to the range though being valid because
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* it means that the receiver is rather inconsistent with itself (reports
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* SACK reneging when it should advance SND.UNA).
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* it means that the receiver is rather inconsistent with itself reporting
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* SACK reneging when it should advance SND.UNA. Such SACK block this is
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* perfectly valid, however, in light of RFC2018 which explicitly states
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* that "SACK block MUST reflect the newest segment. Even if the newest
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* segment is going to be discarded ...", not that it looks very clever
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* in case of head skb. Due to potentional receiver driven attacks, we
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* choose to avoid immediate execution of a walk in write queue due to
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* reneging and defer head skb's loss recovery to standard loss recovery
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* procedure that will eventually trigger (nothing forbids us doing this).
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*
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* Implements also blockage to start_seq wrap-around. Problem lies in the
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* fact that though start_seq (s) is before end_seq (i.e., not reversed),
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