Messages in this thread | | | Subject | Re: [PATCH] tcp: Restore RFC5961-compliant behavior for SYN packets | From | Eric Dumazet <> | Date | Thu, 20 Nov 2014 18:22:07 -0800 |
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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>
Thanks !
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