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Message-ID: <Ymv4GAezJlA1+Vfs@zx2c4.com> Date: Fri, 29 Apr 2022 16:37:12 +0200 From: "Jason A. Donenfeld" <Jason@...c4.com> To: Willy Tarreau <w@....eu>, edumazet@...gle.com Cc: netdev@...r.kernel.org, David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>, Moshe Kol <moshe.kol@...l.huji.ac.il>, Yossi Gilad <yossi.gilad@...l.huji.ac.il>, Amit Klein <aksecurity@...il.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 net 3/7] tcp: resalt the secret every 10 seconds Hi Eric, On Thu, Apr 28, 2022 at 02:39:57PM +0200, Willy Tarreau wrote: > From: Eric Dumazet <edumazet@...gle.com> > > In order to limit the ability for an observer to recognize the source > ports sequence used to contact a set of destinations, we should > periodically shuffle the secret. 10 seconds looks effective enough Nit: "periodically re-salt the input". > without causing particular issues. Just FYI, moving from siphash_3u32 to siphash_4u32 is not free, as it bumps us up from siphash_3u32 to siphash_2u64, which does two more siphash rounds. Maybe this doesn't matter much, but just FYI. I wonder, though, about your "10 seconds looks effective enough without causing particular issues." I surmise from that sentence that a lower value might cause particular issues, but that you found 10 seconds to be okay in practice. Fine. But what happens if one caller hits this at second 9 and the next caller hits it at second 0? In that case, the interval might have been 1 second, not 10. In other words, if you need a certain minimum quantization for this to not cause "particular issues", it might not work the way you wanted it to. Additionally, that problem aside, if you round EPHEMERAL_PORT_SHUFFLE_PERIOD to the nearest power of two, you can turn the expensive division into a bit shift right. Regards, Jason
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