Messages in this thread | | | Date | Fri, 21 Nov 2014 15:34:38 -0500 (EST) | Subject | Re: [PATCH] tcp: Restore RFC5961-compliant behavior for SYN packets | From | David Miller <> |
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From: Eric Dumazet <eric.dumazet@gmail.com> Date: Thu, 20 Nov 2014 18:22:07 -0800
> On Thu, 2014-11-20 at 17:47 -0800, Calvin Owens wrote: > >> That's actually not what led to finding this, but it's a good point. :) >> >> What if the challenge-ACK counter were decremented in tcp_validate_incoming() >> when a valid RST packet is seen? That would allow legitimate remote >> hosts to reestablish connections without being ratelimited, and still >> prevent a malicious host from guessing sequence numbers. >> >> There would need to be a way to tell if a challenge ACK had in fact been >> sent and only decrement in that case, since otherwise a local attacker >> could establish and immediately reset lots of connections to keep the >> counter below the ratelimit threshold and guess sequence numbers. >> >> Simply adding a flag to struct tcp_sock would work: just set the flag >> whenever a challenge ACK is sent, and clear it and decrement the counter >> only if it is set when a valid RST packet is seen. > > Seems tricky, a Challenge ACK do not necessarily gives an RST. > > Anyway this certainly can wait, as we already have a sysctl to > eventually work around the issue. > > Acked-by: Eric Dumazet <edumazet@google.com>
Applied, thanks everyone.
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