Re: Misalignment, MIPS, and ip_hdr(skb)->version

From	Willy Tarreau <w@1wt.eu>
Newsgroups	linux.kernel
Subject	Re: Misalignment, MIPS, and ip_hdr(skb)->version
Date	2016-12-11 17:50 +0100
Message-ID	<sNfu2-1rA-21@gated-at.bofh.it> (permalink)
References	(1 earlier) <sLUUF-7mL-5@gated-at.bofh.it> <sLZ7Y-1LZ-3@gated-at.bofh.it> <sMYjw-7Ui-5@gated-at.bofh.it> <sN6Ap-4DD-13@gated-at.bofh.it> <sNdLA-mT-13@gated-at.bofh.it>
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On Sun, Dec 11, 2016 at 03:50:31PM +0100, Jason A. Donenfeld wrote:
> 3. Add 3 bytes of padding, set to zero, to the encrypted section just
> before the IP header, marked for future use.
> Pros: satisfies IETF mantras, can use those extra bits in the future
> for interesting protocol extensions for authenticated peers.
> Cons: lowers MTU, marginally more difficult to implement but still
> probably just one or two lines of code.
> 
> Of these, I'm leaning toward (3).

Or 4) add one byte to the cleartext header for future use (mostly flags
maybe) and 2 bytes of padding to the encrypted header. This way you get
the following benefits :
  1) your encrypted text is at least 16-bit aligned, maybe it matters
     in your checksum computations on during decryption
  2) your MTU remains even, this is better for both ends
  3) you're free to add some bits either to the encrypted or the clear
     parts.

Just a suggestion :-)

Willy

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Thread

Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-07 19:40 +0100
  Re: Misalignment, MIPS, and ip_hdr(skb)->version Dave Taht <dave.taht@gmail.com> - 2016-12-07 19:50 +0100
    Re: Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-07 20:00 +0100
      Re: Misalignment, MIPS, and ip_hdr(skb)->version David Miller <davem@davemloft.net> - 2016-12-07 21:00 +0100
        Re: Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-08 01:40 +0100
          Re: Misalignment, MIPS, and ip_hdr(skb)->version David Miller <davem@davemloft.net> - 2016-12-08 01:40 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-08 23:30 +0100
              Re: Misalignment, MIPS, and ip_hdr(skb)->version David Miller <davem@davemloft.net> - 2016-12-09 00:20 +0100
              Re: Misalignment, MIPS, and ip_hdr(skb)->version Willy Tarreau <w@1wt.eu> - 2016-12-11 09:10 +0100
                Re: Misalignment, MIPS, and ip_hdr(skb)->version Måns Rullgård <mans@mansr.com> - 2016-12-11 11:50 +0100
      Re: Misalignment, MIPS, and ip_hdr(skb)->version Felix Fietkau <nbd@nbd.name> - 2016-12-10 13:30 +0100
        Re: Misalignment, MIPS, and ip_hdr(skb)->version Måns Rullgård <mans@mansr.com> - 2016-12-10 14:30 +0100
          Re: Misalignment, MIPS, and ip_hdr(skb)->version Felix Fietkau <nbd@nbd.name> - 2016-12-10 21:20 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version Felix Fietkau <nbd@nbd.name> - 2016-12-10 21:40 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version Måns Rullgård <mans@mansr.com> - 2016-12-10 21:40 +0100
          RE: Misalignment, MIPS, and ip_hdr(skb)->version David Laight <David.Laight@ACULAB.COM> - 2016-12-12 17:20 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version Måns Rullgård <mans@mansr.com> - 2016-12-12 17:40 +0100
    Re: Misalignment, MIPS, and ip_hdr(skb)->version David Miller <davem@davemloft.net> - 2016-12-07 20:00 +0100
  Re: Misalignment, MIPS, and ip_hdr(skb)->version Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-08 01:40 +0100
    Re: Misalignment, MIPS, and ip_hdr(skb)->version Daniel Kahn Gillmor <dkg@fifthhorseman.net> - 2016-12-08 06:10 +0100
      Re: Misalignment, MIPS, and ip_hdr(skb)->version Jiri Benc <jbenc@redhat.com> - 2016-12-09 12:30 +0100
      Re: Misalignment, MIPS, and ip_hdr(skb)->version Dan Lüdtke <mail@danrl.com> - 2016-12-10 23:30 +0100
        Re: Misalignment, MIPS, and ip_hdr(skb)->version Greg KH <gregkh@linuxfoundation.org> - 2016-12-11 08:20 +0100
          Re: Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-11 16:00 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-11 16:40 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version Andrew Lunn <andrew@lunn.ch> - 2016-12-11 16:40 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version Willy Tarreau <w@1wt.eu> - 2016-12-11 17:50 +0100

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